Aquaculture tank assembly and related methods

Abstract

A tank segment 102a for an aquaculture tank assembly 100 comprises: a tank base portion 104a; a tank sidewall portion 106a; and at least one peripheral joining edge 108a extending along at least a por

Description

Technical Field The invention relates to a tank segment for an aquaculture tank assembly, a system for forming an aquaculture tank assembly, and to a method of assembling an aquaculture tank assembly. The invention also relates to a self-cleaning aquaculture tank and a method of cleaning an aquaculture tank. Background Established aquaculture tanks are typically manufactured in a first location and then transported to a second location for use. The transit distance can be large, as aquaculture tanks are often used in remote and / or isolated locations with suitable climate and / or conditions for cultivating aquatic organisms. Installation of such aquaculture tanks thus typically requires long-distance transportation methods such as shipping, freight rail or road haulage. As aquaculture tanks are typically large, heavy and cumbersome, their transportation and installation pose logistical challenges both from a size and cost perspective. Modular aquaculture tank assemblies have been developed to try to address this challenge. A modular tank assembly refers to those that are assembled or constructed from a plurality of separate tank wall sections or portions that are provided as a system or kit of components / parts and assembled on site to form the modular tank assembly. Existing modular tank assemblies are typically formed of a multitude of panels which are bolted or otherwise joined together to form the sidewalls and the base of the tank. However, due to the nature of such modular tank assemblies and their construction, they are difficult and time consuming to assemble and construct. They may also be more prone to leaks, structurally less stable, and more difficult to clean compared to traditional tanks due to the multiple seams and joins, often requiring additional liners and / or supporting structures which adds to the complexity of tank installation and maintenance. Aspects and embodiments of the present disclosure have been devised with the foregoing in mind. Summary of the disclosure According to a first of the present invention, there is provided a tank segment for an aquaculture tank assembly or modular aquaculture tank assembly. The tank segment comprises: a tank base portion; a tank sidewall portion; and at least one peripheral joining edge extending along at least a portion of the tank base portion and the sidewall portion; wherein the tank segment is configured to abut and be joined at the at least one peripheral joining edge to at least one other corresponding tank segment to form at least part of an aquaculture tank assembly. By providing a tank segment comprising an integral tank base portion and tank sidewall portion with at least one peripheral joining edge extending along the tank base portion and sidewall portion, the advantage of providing an improved tank segment for use in constructing a modular tank assembly is afforded, reducing the installation time, difficulty and costs associated with a modular aquaculture tank assembly. In particular, the configuration of the tank segment means fewer tank segments are required to be assembled and joined to form the resulting modular tank assembly, which is thereby easier to construct and has improved reliability and structural stability. The configuration of the tank segment, when combined with other like tank segments in a tank assembly, may also reduce the number of seams within the aquaculture tank assembly, thereby making it less prone to leaks and structurally more stable. A peripheral joining edge refers, generally, to a surface or edge of a tank segment which is configured to contact and abut with a peripheral joining edge of another corresponding tank segment, so as to form at part of the assembled aquaculture tank (the tank assembly). As such, the peripheral joining edge is or includes an exterior lateral surface or face of the tank segment, with a surface profile to facilitate such abutment and joining (as opposed to other surfaces of the tank segment which may, for example, form portions of the exterior wall or liquid retaining surface). References to an assembled tank may be refer to a tank assembly, and vice versa. Preferably, the tank base portion extends from the tank sidewall portion and vice versa. Preferably, the tank base portion extends from the tank sidewall portion and tapers in lateral width towards a centre of the assembled aquaculture tank (or towards a distal end of the tank base portion). Preferably, the tank sidewall portion of the tank segment extends from the tank base portion to a rim of the assembled aquaculture tank. Optionally of preferably, the tank segment is configured as quadrant or other substantially vertical section (i.e. a substantially vertical sectional division) of the assembled aquaculture tank or tank assembly. Preferably, the tank base portion and the tank sidewall portion form a continuous inner surface of the assembled aquaculture tank (or tank assembly). By providing a continuous inner surface extending along the sidewall and base portion, seams along the inner surface of the resulting tank assembly are minimised, and the advantage of improved reliability and structural stability with reduced probability of leaks is afforded. Preferably, the tank segment is a unitary structure, and / or formed of a unitary piece of material. Preferably, the tank segment is formed of a (e.g. moulded) thermoplastic material. For the same reasons as above, the same advantage is afforded. In particular, thermoplastic tank segments can provide high strength while at the same time simplifying the manufacture and assembly process by facilitating the use of a moulding process, such as injection moulding (whereby the same mould can be re-used multiple times for different tank segments), and a plastic welding process. Preferably, the tank segment is configured to form, when assembled with other like tank segments, a free-standing aquaculture tank assembly. By providing a freestanding tank, where no (or minimal) additional structural support is required, the advantage of reduced installation costs is afforded. Additionally, the assembled aquaculture tank may be used in more extreme locations and transported more easily. The freestanding nature may be afforded by the increased structural strength and stability of the tank assembly provided by tank segments according to the present invention. Preferably, the tank segment comprises at least one load bearing support portion. Optionally or preferably, the at least one load bearing support portion extends from an underside of, and / or is integrated with, the tank base portion. For the same reasons as above, the same advantage is afforded. Preferably, the tank base portion of the tank segment is configured to form at least a portion of a drain opening in a base of the aquaculture tank assembly. By providing a drain opening, where the drain opening is formed by portions of the tank segment, the advantage of reduced construction costs is afforded. Preferably, the tank segment further comprises at least one opening for receiving at least a portion of a respective first retaining member for use in clamping the tank segment to another corresponding tank segment in an assembled configuration. By providing at least one opening for receiving at least a portion of a respective first retaining member, where the respective first retaining member is insertable into the opening of the tank segment, the advantage of improved assembly of the tank assembly is afforded. In particular, the openings allow retaining members to be used to clamp and hold multiple such tank segments together in an assembled configuration prior to joining, e.g. by welding, and further may provide improved application of a clamping force and reduced strain on the tank segment from the retaining members. Preferably, the at least one opening includes at least one opening in the tank sidewall portion and at least one opening in the tank base portion. For the same reasons as above, the same advantage is afforded. Preferably, the at least one opening is located adjacent to, and extends in a direction substantially parallel to, at least a portion of the at least one peripheral joining edge. Optionally or preferably, the at least one opening includes at least one opening extending at least partially through and along the tank sidewall portion. This configuration of openings may advantageously provide more even application of the clamping force and reduced strain on the tank segment is afforded. The tank segment, and the tank sidewall and base portions, may have first and second lateral sides with at least one respective first and second peripheral joining edge for abutting and joining to other (e.g. different) corresponding tank segments. The first and second lateral sides may be substantially opposite each other. Preferably, the tank segment includes first and second peripheral joining edges extending at least partially along respective first and second lateral sides of the tank sidewall portion and tank base portion. Preferably, the at least one opening in each tank segment includes a first opening located adjacent to, and extending through and along at least part of the tank sidewall portion in a direction substantially parallel to, the first peripheral joining edge. Preferably, the at least one opening in each tank segment further includes a second opening located adjacent to, and extending through and along at least part of the tank sidewall portion in a direction substantially parallel to, the second peripheral joining edge. For the same reasons as above, the same advantage is afforded. Preferably, the at least one opening extends through and along the tank segment. For the same reasons as above, the same advantage is afforded. In particular, this arrangement may allow a respective first retaining member inserted in the opening to be engaged at either end of a peripheral joining edge to provide a more evenly distributed clamping force. According to a second aspect of the present invention, there is provided a system for forming or constructing an aquaculture tank assembly, comprising: a plurality of tank segments, each tank segment comprising: a tank base portion; a tank sidewall portion; and at least one peripheral joining edge extending along at least a portion of the tank base portion and the sidewall portion. The plurality of tank segments are configured to abut along their respective peripheral joining edges (when arranged) in an assembled configuration and be joined at their respective peripheral joining edges to form an assembled aquaculture tank or tank assembly. Preferably, the plurality of tank segments of the system are a plurality of tank segments as defined in the first aspect, and each tank segment can include any or all of the features thereof. By providing a plurality of tank segments that each comprise a tank base portion, a tank sidewall portion and at least one peripheral joining edge extending along the tank base portion and sidewall portion, the advantage of an improved system for constructing a modular tank assembly is afforded, reducing the installation time, difficulty and costs of a modular aquaculture tank. In particular, the resulting modular tank assembly is easier to construct and has improved reliability and structural stability. The configuration of the tank segments may reduce the number of seams within the assembled aquaculture tank, thereby making it less prone to leaks and structurally more stable. References to an assembled tank may be refer to a tank assembly, and vice versa. The plurality of tank segments may be configured to be arranged, in the assembled configuration, circumferentially about a centre (or a centre line) of the assembled aquaculture tank, and preferably symmetrically about a centre of the assembled aquaculture tank. For the same reasons as above, the same advantage is afforded. Preferably, the plurality of tank segments are substantially identical (e.g. in size and shape). By providing substantially identical tank segments, that may e.g. tesselate, the advantage of easier transportation and storage of the tanks segments is afforded. Additionally, by providing identical tank segments, the advantages of easier manufacturing and easily replaceability are afforded, e.g. each tank segment can produced in the same way, and where the tank segments are formed of a plastic material, they may be formed using a single mould. Preferably, the assembled aquaculture tank is a freestanding tank. By providing a freestanding tank, where no (or minimal) additional structural support is required, the advantage of reduced installation costs is afforded. Additionally, the assembled aquaculture tank may be used in more extreme locations and transport more easily. The freestanding nature may be afforded by the increased structural strength and stability of the tank provided by the tank segments. In this case, each tank segment may comprise at least one load bearing support portion as described in the first aspect. Preferably, the system further comprises a plurality of retaining members, wherein the plurality of retaining members are operable to clamp together the plurality of tank segments in the assembled configuration. By providing a plurality of retaining members, where the plurality of retaining members assist in the joining of tank segments, the advantage of quicker and easier construction is afforded. For example, the retaining members may improve and simplify the joining / sealing of adjacent tank segments by holding them in the correct abutted positions during sealing along the peripheral joining edges (e.g. by welding). Preferably, the plurality of retaining members include a plurality of pairs of first retaining members mounted or mountable to the plurality of tank segments, and a plurality of second retaining members operable to releasably engage the respective pairs of first retaining members and exert a clamping force therebetween to thereby clamp together the plurality of tank segments in the assembled configuration. For the same reasons as above, the same advantage is afforded. Preferably, the plurality of retaining members are removably mountable to the tank segments. This may allow them to be removed once the plurality of tank segments are joined. Alternatively, the plurality of first retaining members may remain in place and form part of the assembled aquaculture tank in operation. Preferably, at least one of the plurality of retaining members is configured to be arranged parallel to at least a portion of the at least one peripheral joining edge of each respective tank segment. By providing at least one retaining member arranged parallel to at least a portion of a peripheral joining edge, the advantage of a more evenly distributed clamping force is afforded. Preferably, each first retaining member of a pair is mounted or mountable adjacent a peripheral joining edge of a different one of the plurality of tank segments so as to provide, when engaged by a respective second retaining member, a clamping force between adjacent tank segments in the assembled configuration. For the same reasons as above, the same advantage is afforded. Preferably, the first retaining members are configured to be arranged as internal or integral components of the plurality of tanks segments. By providing the first retaining members as internal components, where the retaining members are substantially located and / or enclosed within a tank segment, the advantage of improved application of the clamping force and reduced strain on the tank segments is afforded. Preferably, each tank segment further comprises at least one opening for receiving at least a portion of a first retaining member of a pair, and wherein the plurality of pairs of first retaining members are insertable into the respective openings of the plurality of tank segments. For the same reasons as above, the same advantage is afforded. Preferably, the first retaining members are insertable into the respective openings in a direction substantially perpendicular to the direction of the clamping force. By providing the first retaining members inserted in a direction substantially perpendicular to the direction of the clamping force, the advantage of maximising efficiency of the clamping force is afforded. Preferably, the at least one opening in each tank segment includes at least one opening in the tank sidewall portion and at least one opening in the tank base portion. For the same reasons as above, the same advantage is afforded. Preferably, the at least one opening in each tank segment is located adjacent to, and extends in a direction substantially parallel to, at least a portion of the at least one peripheral joining edge. Optionally or preferably, the at least one opening includes at least one opening extending at least partially through the tank sidewall portion. For the same reasons as above, the same advantage is afforded. Preferably, each tank segment includes first and second peripheral joining edges extending along at least a portion of respective first and second lateral sides of the tank sidewall portion and the tank base portion. The at least one opening in each tank segment may include: a first opening located adjacent to, and extending through at least part of the tank sidewall portion in a direction substantially parallel to, the first peripheral joining edge; and a second opening located adjacent to, and extending through at least part of the tank sidewall portion in a direction substantially parallel to, the second peripheral joining edge. For the same reasons as above, the same advantage is afforded. Preferably, the at least one opening includes at least one opening that extends through the tank segment. For the same reasons as above, the same advantage is afforded. In particular, this arrangement may allow the respective pair of first retaining members to be engaged at either end of a peripheral joining edge to provide a more evenly distributed clamping force. Preferably, the tank segments and / or the first retaining members are configured such that a distal end of each first retaining member protrude from the respective opening when inserted into the opening. This may provide an accessible or exposed portion of the first retaining members for the second retaining members to engage. Preferably, the plurality of second retaining members are removably attachable to the plurality of pairs of first retaining members. By providing removably attachable second retaining members, where the first and second retaining members may be reused in other tank assemblies, the advantage of reduced construction cost is afforded. The second retaining members may be a threaded retaining member, such as a bolt. The first retaining members may comprise an opening to receive a respective second retaining member. Preferably, the system further comprise a sealing means (or member or apparatus) for use in joining / sealing adjacent tank segments at their respective peripheral joining edges in the assembled configuration the plurality of tank segments. The sealing means is preferably attachable along at least a portion of at least some of the peripheral joining edges of the plurality of tank segments. By providing a sealing means, where the sealing means may assist in preventing leaks at the respective peripheral joining edges, the advantage of improved reliability of the assembled tank is afforded. Preferably, the sealing means comprises one or more elongate electrical heating elements, (such as a metallic cord, wire or cable) operable to heat the surrounding material of the respective tank segments (to which it is attached) to thereby weld adjacent tank segments together at their respective peripheral edges and form the assembled tank. The sealing means preferably comprises a plurality of electrical heating elements, each attachable to a different peripheral joining edge, or portion of a peripheral joining edge. By providing an elongate electrical heating element, where the elongate electrical heating element may be attached to the peripheral joining edge before assembling the tank segments in the assembled configuration, the advantage of quicker construction is afforded. In addition, the electrical heating elements may provide a deep internal weld / join which may thereby provide a stronger join compared to superficial welding processes and thus a more structurally stable assembled tank. The heating elements may be provided or attachable to the external lateral face of the peripheral joining edges. The system may further include a heating control apparatus connectable to the one or more electrical heating elements for controlling the one or more electrical heating elements and the joining / welding process. Preferably, the assembled aquaculture tank further comprises a drain opening located, preferably centrally, in the aquaculture tank base. Optionally or preferably, each tank base portion of the plurality of tank segments comprises a portion of the drain opening. Preferably, the system further comprises a fluid propulsion unit or device mountable at or near the drain opening of the assembled aquaculture tank. The fluid propulsion unit is configured, in use, to output or produce a flow of fluid directed away from the base of the aquaculture tank. By providing a fluid propulsion unit, where the fluid propulsion unit induces a radial flow along the base of the tank, the advantage of a self-cleaning tank function is afforded. Preferably, the fluid propulsion unit is configured, in use, to induce a radial flow of liquid in the assembled aquaculture tank along the base towards to the drain opening, e.g. to direct waste matter entrained in the radial flow towards the drain opening where it can be collected. In this way, the fluid propulsion unit can provide a self-cleaning function. Optionally or preferably, the fluid propulsion unit is configured, in use, to induce a toroidal vortex flow within the liquid in the assembled aquaculture tank. Preferably the fluid is a gas, and the fluid propulsion unit comprises an aeration device. Preferably, the system further comprises a sump tank or settling portion attachable to the drain opening. The sump tank or settling portion may have a set-back surface (i.e. set back with respect to the surface of the base of the assembled tank) for collecting debris entrained in the radial flow that enters the drain opening. The sump tank or settling portion may include a further drain opening or a drain located therein (e.g. for removal of the collected waste matter). The further drain opening or the drain may be located in the set-back surface of the sump tank. By providing a sump tank or settling portion attachable to the drain opening in the base of the assembled tank, where the sump tank may collect and store waste matter, the advantage of increasing the total fraction of waste matter removed from the tank is afforded. In particular, the sump tank or settling portion may collect waste in a region spatially separated from the (main) tank volume and thus inhibit the movement of waste matter back through the drain opening in the (main) tank. The sump tank may comprise a circumferential flange extending laterally outwards from an open end of the sump tank. In this way, the sump tank may be configured to be insertable into the drain opening of the aquaculture tank assembly such that the flange abuts and overlaps the base of the tank assembly around the drain opening. The system may comprise a platform for supporting the fluid propulsion unit at a height above the tank base surface. The platform preferably has a width that is greater than a corresponding width of the fluid propulsion unit. The platform may be attached or attachable to the sump tank. The platform may be supported at the height by a supporting member which extends from a wall of the sump tank, e.g. the set-back surface. The platform may be fixed to a distal end of the supporting member. The height may be fixed and determined by the length of the supporting member. Alternatively, the height of the platform may be adjustable. For example, the platform and / or supporting member can be configured to provide a means for adjusting the height of the platform. According to third aspect of the present invention, there is provided a method of assembling or constructing an aquaculture tank assembly (i.e. a modular aquaculture tank assembly). The method may be a method of assembling the system of the second aspect. The method comprises the steps of: arranging a plurality of tank segments into an assembled configuration, wherein each tank segment comprises a tank base portion, a tank sidewall portion and at least one peripheral joining edge extending along at least a portion of the a tank base portion and the tank sidewall portion, and wherein arranging comprises aligning the plurality of tank segments to abut along their respective peripheral joining edges. The method further comprises joining the plurality of tank segments together in the assembled configuration at the abutted peripheral edges to form the aquaculture tank assembly. Preferably, the plurality of tank segments are a plurality of tank segments as defined in the first aspect, and each tank segment can include any or all of the features thereof. By providing a method of assembling an aquaculture tank assembly comprising the steps of: arranging a plurality of tank segments together in the assembled configuration, wherein the tank segments include tank sidewall and base portions and wherein the tanks segments may be arranged in the assembled configuration before joining, the advantage of improved, simplified and rapid construction and installation of a modular tank is afforded, requiring less time and costs. The resulting assembled tank assembly may have improved reliability and improved structural strength and stability. In particular, the resulting modular tank is easier to construct and has improved reliability and structural stability. Preferably, the step of joining comprises welding adjacent tank segments within the plurality of tank segments together at their respective abutted peripheral edges. Optionally or preferably, the plurality of tank segments are formed of a thermoplastic material and welding comprises using an electrical heating element applied along at least a portion of at least some of the peripheral joining edges of the tank segments. Further preferably, the welding step comprises applying a heating current through, or electrical power to, the heating elements for a period of time to heat the surrounding material of the respective tank segments to or above a melting point of the material. By providing a plurality of tank segments formed of a thermoplastic material, where the electrical heating element heats the surrounding material of the respective tank segments to or above a melting point of the material, the advantage of an improved seal which is more resistant to leaks is provided. Preferably, the method further comprises the steps of: clamping adjacent tank segments within the assembled configuration together using a plurality of retaining members. By providing a plurality of tank segments which may clamp together via the retaining members, the advantage of easier construction is provided. Optionally or preferably, the step of clamping comprises the steps of: inserting at least one first retaining member of the plurality of retaining members into at least one respective opening in each of the plurality of tank segments, and engaging pairs of the first retaining members that are inserted in respective adjacent tank segments with at least one second retaining member of the plurality of retaining members to exert a clamping force between each pair of the first retaining members. Where the tank assembly comprises a drain opening, the method may comprise a step of attaching a sump tank to the drain opening in the tank assembly or assembled tank. Preferably, the sump tank comprises a circumferential flange (or a similar protruding lip) extending laterally outwards from an open end of the sump tank, and the method comprises inserting the sump tank into the drain opening such that the flange abuts and overlaps the tank base surface around the drain opening (i.e. a rim of the drain opening). Preferably, the method further comprises welding the flange to the tank base surface around a peripheral edge of the flange, e.g. with a fillet weld, to form a liquid tight seal therebetween. The method may further comprise supporting a fluid propulsion unit at a height above the drain opening, preferably on a platform with a width greater than a width of the fluid propulsion unit. According to another aspect of the present invention, there is provided an aquaculture tank assembly comprising a plurality of tank segments as defined in the first aspect arranged and / or aligned in an assembled configuration to abut along their respective peripheral joining edges and joined along their respective peripheral joining edges. Preferably, the tank assembly is formed, constructed or produced by the method of the third aspect. According to another aspect of the present invention, there is provided a self-cleaning aquaculture tank. The self-cleaning aquaculture tank may optionally be formed from the system of the second aspect, preferably using the method of the third aspect. The self-cleaning tank comprises: a tank with a base and at least one sidewall; a drain opening in the base (e.g. for removal liquid from the tank); a fluid propulsion unit arranged at or near to the drain opening. The fluid propulsion unit is configured to generate a flow of fluid directed away from the base to displace liquid in the tank and thereby induce a flow (e.g. a radial flow) of liquid along the base towards to the drain opening for directing waste matter entrained in the flow of liquid towards and / or into the drain opening. By providing a self-cleaning aquaculture tank with a fluid propulsion unit, where the fluid propulsion unit allows waste matter to automatically be removed from the tank, the advantage of increased water quality is provided, which may allow a greater quantity or quality of aquatic organisms to be cultivated. Preferably, the fluid propulsion unit further induces a toroidal vortex within liquid in the tank. By inducing a toroidal vortex, where the toroidal vortex may cause buoyant waste matter to be directed towards the drain opening, the advantage of increasing the total fraction of waste matter removed from the tank is afforded. Preferably, the drain opening is located centrally in the base of the tank. Preferably, the drain opening and the fluid propulsion unit are substantially co-located. By co-locating the fluid propulsion unit and the drain opening, where the induced radial flow is towards the drain opening from every angle, the advantage of increasing speed of the removal of waste matter from the tank is afforded. Preferably, the fluid propulsion unit is supported at a predefined height above the drain opening. Preferably, the fluid propulsion unit is supported on a platform at a predefined height above the tank base surface. Preferably, the platform has a width that is substantially greater than a corresponding width of the fluid propulsion unit, such that the fluid propulsion unit is substantially set back from a peripheral edge or rim of the platform. The platform may a fixed height or an adjustable height. Preferably, the fluid is a gas, e.g. air or oxygen. Optionally or preferably, the fluid propulsion unit is or comprises an aeration device. By providing an aeration device, where the aeration device may inject air or oxygen into liquid in the tank, the advantage of increased water quality and resulting improved cultivation of aquatic organisms is afforded. The use of an aeration device to induce the radial flow of liquid may be energy efficient and reduce power consumption of the tank in operation, and may allow the aeration device to be operated for prolonged periods of time and / or substantially continuously. Preferably, the tank further comprises a sump tank or settling portion having a set-back surface for collecting debris entrained in the radial flow. Preferably, the sump tank or settling portion is in fluid communication with the drain opening and / or attached to the drain opening. Preferably, the tank or sump tank includes a drain is located in the set-back surface of the sump tank or settling portion. For the same reasons as above, the same advantage is afforded. The platform may be coupled to the sump tank via a supporting member. The supporting member may be configured to adjust the height of the platform. According to another aspect of the present invention, there is provided a method of cleaning an aquaculture tank, comprising the steps of: generating, using a fluid propulsion unit located adjacent a drain opening in a base of the aquaculture tank, a flow of fluid directed away from a base of the tank to thereby induce a flow of liquid along the base towards to the drain opening to direct waste matter entrained in the flow of liquid towards the drain opening; and collecting waste matter entrained in the flow of liquid at the drain opening. By providing a method of cleaning an aquaculture tank using a fluid propulsion unit, where the fluid propulsion unit allows waste matter to automatically be removed from the tank, the advantage of increased water quality is provided, which may allow a greater quantity or quality of aquatic organisms to be cultivated, and the tank to be operated in a ‘cleaning mode’ for prolonged periods of time. Preferably, the drain opening is located substantially at or near a centre of the aquaculture tank. Preferably, the method further comprises opening a drain in fluid communication with, or coupled to, the drain opening to the to remove collected waste matter from the tank. For the same reasons as above, the same advantage is afforded. Preferably, the fluid propulsion unit comprises an aeration device. For the same reasons as above, the same advantage is afforded. Preferably, collecting waste matter comprises collecting the waste matter in a sump tank or settling portion in fluid communication with, or coupled to, the drain opening. For the same reasons as above, the same advantage is afforded. In this case, the method may further comprise opening a drain in fluid communication with, or coupled to, the sump tank or settling portion to the to remove collected waste matter from the tank. Any feature of the tank segment may be applied to the system or tank assembly. Any feature of the tank segment or system as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure. Any, some and / or all features in one aspect of the disclosure may be applied to other aspects of the disclosure, in any appropriate combination or subcombination. In particular, structure aspects may be applied to method aspects, and vice versa. It should also be appreciated that particular combinations of the various features described and defined in any aspect of the disclosure can be implemented and / or supplied and / or used independently. The disclosure extends to assemblies, tanks, methods, system and structures substantially as herein described and / or as illustrated with reference to the accompanying figures. The disclosure also extends to any novel aspects or features described and / or illustrated herein. In this specification the word 'or' can be interpreted in the exclusive or inclusive sense unless stated otherwise. Brief Description of Drawings In order that the disclosure can be well understood, aspects and embodiments will now be discussed by way of example only with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of system for forming an aquaculture assembly according to an embodiment of the present disclosure; Figure 2 is a schematic diagram of a plurality of tank segments arranged in an assembled configuration, according to an embodiment of the present disclosure; Figures 3(a) and 3(b) show, respectively, schematic diagrams of a tank segment and a plurality of tank segments arranged in an assembled state according to an embodiment of the present disclosure; Figures 4(a) and 4(b) show, respectively, schematic diagrams of tank segments and a plurality of tank segments arranged in an assembled state according to another embodiment of the present disclosure; Figure 5 show a schematic diagram of a tank segment according to another embodiment of the present disclosure; Figure 6 shows a schematic cross-sectional view of a tank segment including support members according to embodiments of the present disclosure; Figures 7(a) and 7(b) show, respectively, a schematic diagram of a tank segment including a sealing means attached thereto, and a cross-sectional view of a peripheral joining edge with the sealing means attached thereto; Figure 8 is a schematic diagram of tank segments being clamped using a plurality of retaining members according to embodiments of the present disclosure; Figure 9(a) is a schematic diagram of a tank segment including a plurality of retaining members mounted thereto according to embodiments of the present invention; Figure 9(b) is a schematic expanded view of two tank segments being clamped by a plurality of retaining members according to an embodiment of the present disclosure; Figure 9(c) is a schematic diagram of a tank segment including a cut-out for accessing a retaining member according to an embodiment of the present disclosure; Figure 10(a) is a schematic diagram of a tank segment comprising a plurality of externally mounted retaining members; Figure 10(b) is a schematic diagram of tank segments including integrated retaining members; Figure 11 shows a schematic diagram of a method of assembling an aquaculture tank assembly according to an embodiment of the present disclosure; Figures 12(a) and 12(b) show schematic cross-sectional and plan view diagrams of a selfcleaning aquaculture tank according to embodiments of the present disclosure; Figure 12(c) shows a schematic cross-sectional view diagram of a self-cleaning aquaculture tank according to another embodiment of the present disclosure; Figure 12(d) shows a schematic cross-sectional view diagram of a fluid propulsion unit supported on a platform according to an embodiment of the present disclosure; Figure 12(e) shows a schematic perspective view diagram of a fluid propulsion unit supported on a platform according to another embodiment of the present disclosure; and Figure 13 shows a schematic diagram of a method ofcleaning an aquaculture tank according to an embodiment of the present disclosure. It should be noted that the figures are diagrammatic and may not be drawn to scale. Relative dimensions and proportions of parts of these figures may have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in modified and / or different embodiments. Detailed Description Figure 1 shows a schematic diagram of a system 100 for forming or constructing an aquaculture tank assembly comprising a plurality or kit of parts for assembling an aquaculture tank assembly according to an embodiment of the present disclosure. The system 100 comprises a plurality of tank segments 102a, 102b which, when assembled, form an aquaculture tank assembly including at least one sidewall and a base defining a liquid holding volume for culturing marine or aquatic organisms. Suitable species or organisms include any water dwelling organisms including but not limited to any species of echinoderms such as sea urchins, molluscs, crustaceans, lobsters, micro- and macroscopic algae, members of the phylum porifera (sponges) or any other benthic organism. The liquid may be sea water or fresh water, depending in the organisms being cultured. Each tank segment 102a, 102b comprises a tank base portion 104a, 104b, a tank sidewall portion 106a, 106b and at least one peripheral joining edge 108a,108b extending along a least a portion of the tank base portion 104a,104b and sidewall portion 106a,106b. The tank sidewall portion 106a, 106b extends from the base portion 104a, 104b, and vice versa. When arranged in an assembled configuration in which the tank segments 102a, 102b are aligned to abut along their respective peripheral joining edges 108a, 108b, and subsequently joined at their abutted peripheral edges 108a, 108b, the tank segments 102a, 102b form an assembled aquaculture tank comprising a base formed of the base portions 104a, 104b and at least one sidewall formed of the sidewall portions 106a, 106b. Because each tank segment 102a, 102b comprises an integral tank base portion 104a, 104b and a tank sidewall portion 106a, 106b there are fewer pieces to be assembled, and the resulting assembled aquaculture tank can be mechanically more stable and can form a freestanding aquaculture tank which may not require further structural support. Advantageously, this may facilitate a more rapid and simplified construction of an aquaculture tank, which may be less prone to leaks thus avoiding the need for a separate liner, and hold an increased volume of liquid without additional structural support. In various embodiments, the system 100 may comprise further components including one or more of: a sealing means 120, a plurality of retaining members 140, a fluid propulsion assembly / unit 160, and a sump tank 180, as will be described in more detail below. The tank segments 102a, 102b can be used to construct any shaped tank, including but not limited to substantially circular, square and rectangular tanks, by appropriate configuration of their shape, as will be described in more detail below. Preferably, the tank segments 102a, 102b are formed of a thermoplastic material to facilitate manufacture by a moulding process and / or sealing / joining by low temperature plastic welding processes, as will be described below, both of which promote ease of manufacture and assembly. However, it will be appreciated that the tank segments can in principle be formed of any suitable material for an aquaculture tank, including metal. The tank sidewall portion 106a, 106b generally defines a portion of a tank segment 102a, 102b which, in the assembled configuration, extends generally upwards from the tank base portion 104a, 104b, preferably to a rim of the assembled aquaculture tank. A rim may refer to an upper edge, lip, brim or perimeter of the assembled aquaculture tank, which is the top of the tank in normal use. The rim may further be a portion of the assembled aquaculture tank which extends ‘above’ the surface of liquid in the assembled aquaculture tank and / or defines a circumference of an open side surface of the assembled aquaculture tank. The tank base portion 104a generally defines a portion of the tank segment 102a, 102b that extends from the tank sidewall portion 104a,104b towards a centre of the assembled aquaculture tank. The tank base portion 104a, 104b and sidewall portion 106a, 106b each include a portion of the respective inner base and sidewall surfaces of the assembled tank (i.e. a liquid contacting surface, and / or surface facing the interior liquid holding volume of the assembled tank) which may be substantially flat, bent or curved as required by the specific configuration of the assembled tank. A peripheral joining edge 108a, 108b refers, generally, to a surface or edge of a tank segment 102a, 102b which is configured to contact and abut with a peripheral joining edge 108a, 108b of another tank segment 102a, 102b. As such, the peripheral joining edge 108a, 108b includes an exterior lateral face or surface (e.g., see surface 1081 in figure 7(b)) of the tank segment 102a, 102b (i.e. distinct from the inner surface of the tank sidewall and base portions 104a, 106a) configured with a surface profile / shape to abut with a corresponding lateral face or surface of a peripheral joining edge of an adjacent tank segment when in the assembled configuration. In its simplest form, the surface profile of the peripheral joining edges 108a, 108b is substantially flat, however, this is not essential. In general, the peripheral joining edges 108a, 108b may have any surface profile which allows one tank segment to fit, tessellate or share a common boundary with another tank segment in the assembled configuration so as to form a continuous seam in the assembled tank that can form a seal or be sealed. In some examples, a peripheral joining edge 108a of a first tank segment 102a may comprise a number of protrusions and / or depressions configured to fit with one or more complementary protrusions and / or depressions of a peripheral joining edge 108b of a second tank segment 102b, such that the first tank segment 108a and second tank segment 108b can fit and interlock together when in the assembled configuration (i.e. when the peripheral joining edges 108a, 108b are brought together into abutment). The provision of complementary surface features of the peripheral edges 108a-108b may assist with alignment of the plurality of tank segments 108a, 108b during assembly. Additionally or alternatively, in another example, the peripheral joining edge of a first tank segment may be formed as a curved or sawtooth (or ‘zig zag’) edge or surface and a second tank segment may comprise a reciprocal / inverse edge or surface such that the peripheral joining edges may similarly fit and interlock / interleave. It will be understood that a multitude of other possible cooperative surface or edge profiles / shapes exist which may allow the plurality of tank segments 102a, 102b to fit and / or abut together to form an assembled tank. It will further be understood that by forming a common boundary, a first and a second tank segment (such as tank segments 102a, 102b) can be joined to form a liquid tight seal, preferably using a sealing means 120 and / or retaining members 140, to facilitate the assembled aquaculture tank holding / retaining liquid without the need for a separate liner, as described in more detail below. Figure 2 shows a schematic side view of a plurality of tank segments 102a, 102b, 102c in an assembled configuration, in which the tank segments 102a-102c are aligned to abut along their respective peripheral joining edges 108a-108c. In this illustrative example, each tank segment 102a-102c comprises two peripheral joining edges 108a-1, 108a-2, 108b-1, 108b-2, 108c-1, 108c-2arranged on opposite lateral sides of the of the respective tank segment 102a-102c, , and the tank segments 102a-102c are shown arranged in a line, such that peripheral joining edge 108a-2 of tank segment 102a abuts peripheral joining edge 108b-1 of tank segment 102b, and peripheral joining edge 108b-2 of tank segment 102b abuts peripheral joining edge 108c-1 of tank segment 102c. However, it will be understood that, typically, the tank segments 102a-102c will be arranged in a ‘closed loop’ in the assembled configuration so as to form a liquid holding assembled tank. For example, peripheral joining edge 108a-1 of tank segment 102a may abut peripheral joining edge 108c-2 of tank segment 102c, or any number of an additional tank segments arranged therebetween (not shown). The peripheral joining edges 108a-1, 108a-2 of a given tank segment 102a may be connected, e.g. at a vertex or corner of the tank base portion 104a, or disconnected, e.g. separated by a non-joining edge of the tank base portion 104a which does not join to another tank segment (such as an edge that forms part of an opening), but in either case they form distinct joining edges of the respective tank segment 102a. By way of example, the rim of the assembled tank is a non-joining edge. Further, although figure 2 shows tank segments 102a-102c with two distinct joining edges 108a-1 108b2, 108b-1, 108b-2, 108c-1, 108c-2, it will be appreciated that, depending on the configuration of the assembled tank and / or the shape and number of tank segments that make up the assembled tank, each tank segment 102a-102c may comprise fewer or more peripheral joining edges. For example, where the system 100 comprises only two tank segments 102a, 102b (e.g. two halves of a tank), each tank segment 102a, 102b may comprise a single contiguous peripheral joining edge 108a, 108b. In most other cases, where there are more than two tank segments 102a-102c that make up the assembled tank, the tank segments 102a-103c will typically comprise multiple distinct peripheral joining edges, whether connected (at vertices) or disconnected (separated by a non-joining edge). Figure 3(a) shows a perspective view of a tank segment 102a according to a specific embodiment of the system 100 for forming a substantially square or rectangular tank assembly (i.e. having a square or rectangular base). The tank segment 102a comprises a tank base portion 104a, a tank sidewall portion 106a, and two peripheral joining edges 108a-1, 108a-2. Each peripheral joining edge 108a-1, 108a-2 extends along a lateral side ofthe tank base portion 104a and the sidewall portion 106a, and is substantially ‘L-shaped’, i.e. formed of two straight sections that are substantially perpendicular to each other. The peripheral joining edge 108a-1, 108a-2 are further connected at a vertex 104v in the base portion 104a, which may correspond to a centre point CP of the assembled tank. In this example, the base portion 104a is substantially square-shaped with four sides, and the sidewall portion 106a comprises two substantially flat wall sections extending from two adjacent sides of the base portion 104a, such that the tank segment 102a has a substantially cubic shape which is open on three sides. In other examples, a square or rectangular tank can be formed from tank segments 102a, 102b with a substantially triangularshaped base portion 104a and a substantially flat sidewall portion 106a extending from one side of the triangular base portion 104a (not shown). Further, it will be appreciated that a perpendicular sidewall and base configuration is not essential, and in in other examples, the assembled tank may instead have a sloped base and / or a sloped sidewall(s). Figure 3(b) shows a perspective view of four of such tank segments 102a-102d arranged in an assembled configuration. As shown, the peripheral joining edge 108a-1 of tank segment 102a abuts to tank segment 102b and the peripheral joining edge 108a-2 of tank segment 102a abuts to tank segment 102d. The peripheral joining edges of tank segment 102b similarly abut to tank segments 102a and 102c and similarly for tanks segments 102c and 102d. As described above, once arranged in the assembled configuration as shown, the plurality of tank segments 102a-102d can be joined at their peripheral joining edges to form an assembled aquaculture tank, whereby the tank sidewall portions 106a-106d of each tank segment 102a-102d collectively form the sidewall of the assembled aquaculture tank and the tank base portions 104a-104d of each tank segment 102a-d collectively form the base of the assembled aquaculture tank. Figure 4(a) shows a schematic perspective view of two tank segments 102a, 102b according to an embodiment of the system 100 for forming a substantially circular aquaculture tank. In this case, the tank segments 102a, 102b each comprise a curved tank sidewall portion 106a, 106b, and the tank base portion 104a, 104b is shaped and configured as a sector of the circular base of the assembled tank. Similar to the square tank segments of figure 3(a), the circular tank segments 102a, 102b comprise two peripheral joining edges 108a-1, 108a-2 which are substantially ‘L-shaped’ and connect at a vertex 104v of the base portion 104a, 102b to form an angle 9, as shown. Figure 4(b) shows a plan view of a plurality of circular tank segments 102a-102d in an assembled configuration forming a substantially circular or cylindrical aquaculture tank, as described above. As shown, each tank segment 102a, 102b comprises two peripheral joining edges 108a-1, 108a-2, 108b-1, 108b-2 that extend radially away from a centre point CP of the assembled tank along either side of the respective base portion 104a, 104b and sidewall portion 106a, 106b. In some embodiments, the assembled tank further includes a central drain opening D located in the aquaculture tank base. In this example, the circular tank segments 102a-102d are substantially identical and each tank base portion 304a-d forms a portion of the drain opening D of the assembled aquaculture tank in the assembled configuration. However, it will be appreciated that the drain opening D need not be centrally disposed, and in general, at least one tank segment 102a-102d forms at least a portion of the drain opening D. The assembled tank may further include additional drain openings, as required (not shown). Figure 5(a) shows a schematic perspective view of two example tank segments 102a, 102b in which the tank base portion 104a, 104b and tank sidewall portion 106a, 106b of the tank segments 102a, 102b form a continuous inner surface (specifically a singular curved surface) of the assembled aquaculture tank, such that there is no specific boundary / division between the tank sidewall portion 106a, 106b and tank base portion 104a, 104b. Similar to figure 4(a), the curved tank segments 102a, 102b comprise two peripheral joining edges 108a-1, 108a-2 which connect at a vertex 104v of the base portion 104a, 102b to form an angle 9. The example in figure 5 may be suitable for forming a substantially hemispherical or bowl-shaped tank, or corner sections of a tank in combination with other shaped tank segments 102a, 102b. Returning to figures 3(b) and 4(b), the system 100 is shown comprising four tank segments 102a-102d such that each tank segment forms a corner, or quadrant, of the assembled aquaculture tank. However, it will be appreciated that the number of tank segments within the system 100 may vary depending on the specific implementation and / or shape of the tank segments. In one example, tank segments 102a and 102b in figures 3(b) and 4(b) may be combined to form a single first tank segment and tank segments 102c and 102d may be combined to form a single second tank segment such that system 100 comprises two tank segments (i.e. two halves) which may be assembled to form an assembled aquaculture tank. In general, the aquaculture tank system 100 comprises a minimum of two tank segments but typically system 100 comprises 3 or more tank segments. In another example, with reference to figures 4(a), 4(b) and 5, the number of tank segments 102a, 102d required to form the circular or hemispherical assembled aquaculture tank may depend on the angle 0 of the sector formed by the tank base portion 104a, 104b (with a smaller angle 0 of the sector typically increasing the number of tank segments required). In preferred embodiments, the plurality of tanks segments 102a-102d that make up an assembled tank are substantially identical, as shown in figures 3(b) and 4(b). This may simplify manufacture and assembly, and in the case of moulded thermoplastic tank segments, may allow the use of a single mould. However, it will be understood that, in general, this is not essential and the assembled tank can in principle be formed from a plurality of different shaped tank segments provided they are configured to abut along their peripheral joining edges 108a-108d. In figures 3(b) and 4(b), the plurality of tank segments 102a-102d are arranged circumferentially about a centre point CP of the assembled aquaculture tank such that the tank base portion 104a of each tank segment 102a-d extends substantially radially outwards from the centre point CP. For substantially square or circular tanks, the tank base portions 104a-104d taper in width towards the centre point CP of the assembled tank. Furthermore, in the embodiment shown in figures 3(b) and 4(b) with identical shaped tank segments 102a-102d, the circumferential arrangement is radially symmetric about the centre point CP. However, it will be understood that in some embodiments, the assembled tank may comprise a central line (instead of central point), for example, in a substantially rectangular aquaculture tank (not shown). In such embodiments, not every tank segment will be identical but the tank base portion 104a of each tank segment 102a-102d may extend generally away from the centre line when in the assembled configuration (not shown). Although various example shapes of tank segments are described above, it will be understood that a number of other tank segment shapes are possible, provided each tank segment can abut with one or more other tank segments along its peripheral joining edges, as described above. In preferred embodiments, the tank segments 102a-102d are configured to form an assembled tank that is free standing. For this purpose, the tank base portions 104a, 104b and the assembled tank may have a substantially flat bottom, as shown in figures 3(a), 3(b), 4(a), 4(b). Alternatively, in some embodiments, each of the plurality of tank segments 102a-102d comprises at least one load bearing support member 110a-d extending from the tank base portion 104a to support the assembled tank in a upright position and / or an elevated position above a surface S in normal use, as shown schematically in the cross-sectional diagram of figure 6. It will be understood that the load bearing support member(s) 110a may also improve the rigidity / resilience of the tank sidewall portion 106a and / or the tank base portion 104a such that thinner materials may be used to manufacture the tank sidewall portion 106a and / or the tank base portion 104a than could have otherwise been used. In some embodiments, an system 100 may be configured to abut and be joined to a pre-existing wall (or feature), wherein at least one peripheral joining edge 108a-1 abuts the pre-existing wall such that, in an assembled configuration, the pre-existing wall forms a part of a sidewall and / or base of the assembled aquaculture tank. In such embodiments, a lower number of tank segments may be sufficient to form an assembled aquaculture tank suitable for retaining liquid. For example, two tank segments similar to the tank segment 102a shown in figures 3(a), 4(a), or 5 may abut a pre-existing wall to form an assembled aquaculture tank suitable for retaining liquid. Typically, aquaculture tanks are open at a top, however, it will be appreciated that in some embodiments it may be beneficial for a tank to be fully enclosed (e.g. to facilitate the cultivation of deep sea or nocturnal species). In such embodiments, the system 100 may further comprise one or more tank cover or lid portions for forming a cover or lid that fits over or onto the tank sidewalls to substantially close the tank, or enclose the liquid holding volume of the tank (not shown). For example, the lid may fit onto or be mounted to a rim of the assembled tank formed by the tank sidewall portions 106a-106d. The system 100 may comprise a plurality of one or more tank lid portions that are configured to abut and be joined at respective peripheral joining edges to form an assembled tank lid (not shown). Preferably, each tank segment 102a-102d is manufactured as a unitary structure, and / or formed of a unitary piece of material. In preferred embodiments, the plurality of tank segments 102a-102d are formed from a plastic material using a moulding process such as, but are not limited to: injection moulding, compression moulding, extrusion or 3D printing methods such as fused filament fabrication (also known as fused deposition modelling). For example, a moulded thermoplastic material may be used to form said unitary structure. Suitable thermoplastic materials (also known as thermo-softening material) may include, but are not limited to: forms of acrylic (such as polyacrylic acids and polymethyl-methacrylate), acrylonitrile butadiene styrene (commonly known as ABS), nylon compounds, polylactic acid, polycarbonate based materials (typically containing bisphenol A) or any other synthetic polyether-, polyphenyl-, polyoxy-, or polypropyl- based thermo-softening material. In another example, the plurality of tank segments 102a-102d are formed from a thermo-setting plastic (or polymer), wherein thermo-setting plastic may include, but is not limited to: epoxy or polyester resin, polyimides, polyurethanes or cyanate esters. It will be understood that a multitude of compounds and variants of the above listed chemicals exist, and that thermoplastic (or thermo-setting plastic) may generally refer to any such similar compound or variant thereof. The use of plastic material may advantageously reduce the manufacture cost, weight, and total quantity of joins or seams located along inner surfaces of the tank and hence reduce the risk of leaks through any such seam. However, it will be appreciated that the tank segments 102a-102d may in general be manufactured using any suitable liquid-impermeable material such that the assembled tank is suitable for retaining liquid. For example, the plurality of tank segments 102a-102d may instead be manufactured from a metallic material. As described above, the plurality of tank segments 102a-102d, shown in an assembled configuration in figures 3b and 4b, are configured to be joined at their peripheral joining edges 108a-108d to form an assembled aquaculture tank. It will be understood that there are various suitable methods which may be used to facilitate joining two peripheral joining edges (and hence two tank segments) together, preferred examples of which are described below. Preferably, the system 100 further comprises a sealing means 120 that is attached or attachable along at least some of the peripheral joining edges 108a-108d of the plurality of tank segments 102a-102d for use in sealing adjacent tank segments within the assembled configuration together at their respective peripheral joining edges 108a, 108b. Figure 7(a) shows a schematic diagram of a tank segment 102a including sealing means 120 attached or provided on the peripheral edges 108a-1, 108a-2. The sealing means 120 can be attached to the peripheral joining edges 108a-1, 108a-2 prior to arranging the tank segments in the assembled configuration. As described above, each peripheral joining edge 108a includes a lateral face or surface 1081 which abuts a corresponding lateral face of an adjacent tank segment when in the assembled configuration, and the sealing means 120 is provided on the lateral face 1081, as illustrated in figure 7(b). In preferred embodiments, the sealing means 120 is a fusing means for welding two adjacent peripheral edges 108a, 108b together into a unitary structure. Where the tank segments 102a, 102b are formed of a plastic material, the fusing means is preferably an electrofusion means, whereby the sealing means 120 comprises a plurality of electrical heating elements 120h attached or attachable to and along the peripheral joining edges 108a, 108b operable to heat and melt the surrounding plastic material of the tank segments 108a, 108b at their peripheral joining edges 108a, 108b to thereby weld said peripheral joining edges 108a, 108b together. In such embodiments, the electrical heating elements 120h may be implemented as an elongate metallic wire or cord attachable along a peripheral joining edge 108a, 108b. The electrical heating elements 120h are connectable to a heating apparatus 120a via connectors 120c for applying a suitable heating current to the electrical heating elements 120h and controlling the welding process. In this case, once joined, the electrical heating element 120h remains in place, encapsulated by the material of the tank segments 108a, 108b. Advantageously, an electrofusion means 120 may provide a strong internal weld at the abutted peripheral edges and a liquid tight join between tank segments. Once joined using the fusing means 120, additional welding may be performed along the joins as required to create a substantially smooth continuous inner surface of the tank. However, it will be understood that the specific implementation of the fusing means will depend on the material used to manufacture the plurality of tank segments 102a-102d. For example, in embodiments wherein the tank segments 102a-102d are constructed of a metallic material, the fusing means may be implemented via a thermal metal welding process. In other embodiments the sealing means 120 is an adhesive (e.g. a form of glue) or a gasket such as a polymeric sealing member. Such sealing means 120 may be suitable for smaller tanks and / or embodiments where tank segments are clamped together with retaining members which can provide the structural support, as described in more detail below. Suitable adhesives for plastic tank segments may include, but are not limited to any / all of: polyvinyl acetate (PVA) glue, cyanoacrylate glue, polyurethane glue, any thermoplastic adhesive, acrylic glue, epoxy resin, contact cement or wax or any other similarly adhesive substance. It will be understood that the choice of adhesive may depend on the material used to manufacture the plurality of tank segments 102a-102d (and hence the material of the peripheral joining edges 108a-108d), where, for example, if the plurality of tank segments 102a-102d are manufactured of a metallic material, then a specific adhesive may be more optimised to bond with a metallic material and hence may be preferable in such an implementation. In preferred embodiments, the system 100 includes a plurality of retaining members 140 operable to clamp together the plurality of tank segments 102a-102d in the assembled configuration. The retaining members 140 may assist in the joining of tank segments 102a-102d by holding them together in the correct positions of the assembled configuration during the welding process described above. In this case, the retaining member 140 are preferably removed after the welding process is completed. Additionally or alternatively, the retaining members 140 themselves may serve to join the tank segments 102a-102d without the use of welding, e.g. with the use of a sealing means 120 such as a gasket or adhesive, described above (in which case the retaining members 140 remain in place and will form part of the assembled tank). Figure 8 illustrates the clamping of two tank segments 102a, 102b together at their respective peripheral edges 108a-2, 108b-1 using the retaining members 140. The plurality of retaining members 140 include a plurality of pairs of first retaining members 141, each one of the pair of first retaining members 141 mounted or mountable to a different tank segment 102a-102d, and a plurality of second retaining members 142 operable to releasably engage the respective pairs of first retaining members 141b and exert a clamping force CF therebetween to thereby clamp together the plurality of tank segments in the assembled configuration, as shown s. The first retaining members 141 are preferably mounted or mountable at locations adjacent or near to a peripheral edge 108a-108d of the respective tank segment 102a-102d. Each first retaining member 141 on a tank segment 102a-102d forms one of a pair of first retaining members 141. As such, when the tank segments 102a-102d are arranged in the assembled configuration, adjacent first retaining members 141 on adjacent tank segments 102a, 102b form pairs located on either side of a join / seam that can be engaged with one or more second retaining members 142 to exert a clamping force CF therebetween and clamp the peripheral joining edges 108a-1, 108b-1 together, as shown in figure 8. Preferably, for each tank segment 102a-102d, at least one first retaining member 141 is mounted or mountable to the tank sidewall portion 106a and at least one first retaining member 141 is mounted or mountable to the tank base portion 104a, so as to provide a distributed clamping force CF at multiple points along a join / seam. In general, the second retaining members 142 allow pairs of first retaining members 141 to be removably affixed together in a reliable and rigid connection which may be reversed by the removal of the one or more of the second retaining members 142 used to engage the pair of first retaining members 141. Preferably, the second retaining members 142 comprise a threaded fastener, such as a bolt or the like, that engages the pair of first retaining members 141 through openings (that can be threaded or unthreaded) in the pair of first retaining members 141, e.g. using one or more nuts or a threaded opening in one of the pairs of first retaining members 141. Alternatively, the second retaining members 142 may comprise a clamp with jaws for exerting a compressive force between the pair of first retaining members 141, such as a g-clamp or similar clamping means. In general, the plurality of first retaining members 141 are one or more structures mounted or mountable on / to one or more of tank segments 102a-102d at a position that is fixed relative to the tank segments 102a-102d at least in the direction of the clamping force CF such that the clamping force CF exerted on the pairs of first retaining members 141a, 141b acts to move and clamp the tank segments 102a-102d together. For this purpose, it will be appreciated that the first retaining members 141 can take a variety of forms, and can be mounted internally within, or externally to, walls (i.e. that define the tank base sidewall and / or base portion) of the tank segments, as described in more detail below. Figure 9(a) shows a schematic side view of a tank segment 102a with a plurality of first elongate retaining members 141a mounted internally within the walls of the tank segment 102a, according to preferred embodiments of the present disclosure. The tank segment 102a comprises an opening 116a in the tank sidewall portion 106a and an opening 114o in the tank base portion 104a for receiving at least a portion of a respective first retaining member 141. The first retaining members 141 are insertable into the respective openings 116a, 114b of the tank segment 102a during assembly to thereby facilitate the clamping function, as described above. In this case, the first retaining members 141 are substantially rigid elongate members, such a metal bar or rodlike member, configured fit and be removably inserted into the openings 116a, 114a. This arrangement of insertable elongate first retaining members 141 may advantageously allow for swift mounting, and a distributed clamping force CF to be applied more evenly across the peripheral joining edge 108a-1. The openings 116a, 114a extend at least partially through a wall of the tank sidewall portions 106a and tank base portions 106a in a longitudinal direction of the wall (i.e. not in a thickness direction of the wall) substantially perpendicular to the direction of the clamping force CF (as indicated by the dashed lines in figure 9(a)). Preferably, the openings 116a, 114a are located adjacent to, and extend in a direction substantially parallel to, the peripheral joining edge 108a-1. This may advantageously allow the second retaining members 142 to apply the clamping force more efficiently (i.e. at right angles to the pairs of first retaining members 141). In this case, the first retaining member 141 inserted into the opening 116a in the tank sidewall portion 106a is preferably arranged substantially vertically and the first retaining member 141 inserted into the opening 114a in the tank base portion 104a is preferably arranged substantially horizontally, as indicated in figure 9(a). Although only one peripheral joining edge 108a-1 is shown, it will be appreciated that similar openings 116a, 114a will be provided adjacent other peripheral joining edges 108a-2 of the tank segment 102a (not shown). It will also be appreciated that other tank segments 102b-102d of the system 100 are configured in substantially the same way, such that first retaining members 141 can be inserted along the respective peripheral joining edges 108b-108d to facilitate clamping together adjacent tank segments in the assembled configuration. As shown in figure 9(a), the first retaining members 141 are configured such that, when inserted into the respective openings 116a, 114a, a distal end portion 1410 of the respective first retaining member 141 protrudes from the respective opening 116a, 114a for engaging with one or more second retaining members 142, as described below. In some embodiments, one or more of the openings 116a, 114a can extend all the way through the tank segment 102a such that the respective opening 114a has two open sides and a distal end portion 1410a of a first retaining member 141 can protrude from each respective side of the opening 114a, 116a. In this way, each distal end portion 1410 of a first retaining member 141 can be engaged by a separate second retaining member 142 to provide a more even clamping force along the entire peripheral joining edge 108a of the base and / or sidewall portion. By way of example, with reference to figure 9(a), the opening 114a in the base portion 104a extends through the tank segment 102a and has two open sides 114a-1, 114a-2 (located on opposite sides of the tank segment 102a) from which respective distal end portions 1410-1, 1410-2 of the first retaining member 141 protrude. Figure 9b shows a schematic diagram of part of a tank sidewall portion 106a of tank segment 102a and part of a tank sidewall portion 106b of tank segment 102b arranged side by side in the assembled configuration, wherein the peripheral joining edge 108a-2 of tank segment 102a abuts the peripheral joining edge 108b-1 of tank segment 102b. Each tank segment 102a, 102b comprises an opening 116a extending at least partially through the wall of the sidewall portion 106a, 106b into which respective first retaining members 141 are inserted, as described above. The two adjacent first retaining members 141 shown in figure 9(b) thus form a pair of first retaining members 141. As described above, each first retaining member 141 comprises a distal end portion 1410 which protrudes from the respective opening 116a, 116b for engaging by a second retaining member 142. In this example, a second retaining member 142 is shown engaged with the first retaining members 141 to exert a clamping force CF therebetween, such that peripheral joining edges 108a-1 and 108b-1 are pulled or otherwise held together for joining, preferably welding, tank segments 102a, 102b together with the sealing mean 120 as described above. Specifically, in this example, the second retaining member 142 comprises a threaded fastener, such as a bolt, which extends through respective openings 1412 in the distal end portions 1410, and which may threadedly engage a nut or threads on one of the openings 1412 (not shown) to exert the clamping force CF. In other embodiments, the tank segment 102a may comprise one or more cutouts or recesses 118a in a wall of the tank sidewall portion 106a and / or the tank base portion 104a to expose and provide access to the distal end portion(s) 1410 of the first retaining member 141 without the distal end portion(s) 1410 protruding beyond the tank segment 102a, as shown schematically in figure 9c. This may be preferable in certain cases where it is undesirable for the distal end 1410 to protrude from the tank segment 102a. Figure 10(a) shows a schematic diagram of a tank segment 102a with a plurality of first retaining members 141 mounted externally to the walls of the tank segment 102a, according to another embodiment. Externally mounted retaining members 141 may be preferably for metal tank segments 102a. In this example, each first retaining member 141 is mounted or attached to a wall of the tank segment 102a adjacent a peripheral joining edge 108a-1, 108a-2 and forms one of a pair of first retaining members 141. Similarly to the internally mounted first retaining members 141 described above with reference to figures 9(a)-9(c), the externally mounted first retaining members 141 are preferably located adjacent to at least a portion of one of the peripheral joining edges 108a-1, 108a-2, and can be engaged by one or more second retaining members 142 in the same way. It will be understood that each peripheral joining edge 108a-1, 108a-2 may have one or a plurality of first retaining members 141 attached adjacent thereto. For example, first retaining members 141 which are relatively shorter than those shown in figure 10(a) may be disposed along the peripheral joining edges 108a-1, 108a-2 spaced at intervals. In the example shown in figure 10(a), the first retaining members 141 are bar-like members mounted to the tank segment 102 via struts. However, in other examples, the first retaining members 141 may take other forms and / or be integrated with the wall of the tank segment 102a, e.g. as a flange formed by a projection or a cutout / recess 118a, as illustrated in figure 10(b) which shows a second retaining member 142 engaged with integral flanges on adjacent tank segments 102a, 102b that form a pair of first retaining members 141. While the first retaining members 141 shown in figures 9(a)-9(c) as substantially straight elongate members, it will be understood that the shape of the retaining members 141 may be dependent on the shape of the tank segments 102a-102d. For example, where a tank segment comprises an at least partially curved peripheral joining edge 108a or base or sidewall portion 104a, 106a, the first retaining members 141 of said tank segment may form a concentric arc with said curved peripheral joining edge 108a or base sidewall portion 104a, 106a. In preferred embodiments, the sealing means 120 of figure 7(a) and plurality of retaining members 141, 142 of figures 8-10(b) are used in conjunction to cooperatively improve the assembly and joining of tank segments 102a-102d along their peripheral joining edges 108a-108d. For example, the retaining members 141, 142 may be used to removably attach the tank segments together in the assembled configuration, such that the sealing means 120 can more effectively join and seal the tank segments. Where the sealing means 120 is an electrofusion means, the retaining members 141, 142 can be removed after the tank segments 102a-102d have been welded together. Alternatively, and / or for other non-permanent sealing means 120 such as adhesive or a gasket, the retaining members 141, 142 can remain in place to maintain an effective seal / join through the persistent clamping force CF. With reference again to figure 4(b), where the assembled aquaculture tank includes a drain opening D, in some embodiments, the system 100 further comprises a fluid propulsion unit 160 mountable at, near, or over, the central drain opening D of the assembled aquaculture tank for generating / outputting a flow of fluid directed away from the tank base and drain opening D. The fluid propulsion unit 160 is configured, in use, to induce a radial flow of liquid in the assembled aquaculture tank along the base of the tank towards to the central drain opening D to direct waste matter entrained in the radial flow towards the drain opening D where it can be collected. In this way, the fluid propulsion unit 160 provides a self-cleaning function, as will be described in more detail below with reference to figures 12(a)-12(e). In preferred embodiments, the fluid propulsion unit 160 is an aeration device, such as an air-injection type aerator, to thereby provide aeration in additional to the self-cleaning function. In preferred embodiments, the system 100 further comprises a sump tank or settling portion 180 attachable at or to the drain opening D to provide a space with a set-back surface in fluid communication with the drain opening D for receiving and collecting debris and / or waste matter entrained in the radial flow, as will be described in more detail below with reference to figures 12(a)-12(d). The sump tank 180 preferably includes a drain or outlet, e.g. located in, or adjacent to the set-back surface, for removing at least a portion of liquid and the collected debris from the sump tank 180. A sump tank is a term of the art and refers to a subsidiary tank or compartment in an aquaculture system, typically located beneath a main tank, in which preferably no aquatic organisms are cultured or housed. In this case, the tank segments 102a-102d provide, when assembled, a main tank and the sump tank 180 is connectable to the drain opening D, preferably using a welding process. The sump tank 180 may comprise a single tank (or set back surface), or a plurality of separate sump tanks. A mesh or filter may be provided across the entrance to the sump tank 180 to prevent aquatic organisms from entering the sump tank 180 while permitting debris to enter. In preferred examples, the sump tank 180 is insertable into the drain opening D of the assembled aquaculture tank after the tank segments 102a-102c are joined, and comprises a circumferential flange 180f (or a similar protruding lip) extending laterally outwards from an open end of the sump tank 180. The flange 180f is arranged to overlap the tank base surface 704s around the drain opening D (i.e. a rim of the drain opening D) to facilitate ease of installation and forming a liquid tight seal. For example, once the sump tank 180 is inserted into the drain opening D such that the flange abuts the rim of the drain opening D, the flange 180f can be welded to the tank base surface 704s around the periphery of the flange 180f, e.g. with a fillet weld, to form a liquid tight seal. For this purpose, it will be appreciated that at least the flange 180f of the sump tank 180 is preferably formed of the same material as the tank segments, e.g. a substantially rigid thermoplastics material. Alternatively, a liquid-tight seal may be formed using a sealing ring placed between the flange 180f and the rim of the drain opening D, e.g. by fastening the flange 180f against the rim of the drain opening D to thereby compress the sealing ring. It will be understood that providing the sump tank as a separate component may allow the sump tank 180 to be more easily replaced (in case of wear or damage to the sump tank) and / or to be manufactured more cheaply and quickly. Figure 11 shows a schematic flow diagram of a method 600 of assembling an aquaculture tank assembly of system 100 according to an embodiment of the disclosure. In step 610, the method 600 comprises arranging the plurality of tank segments 102a-102d into an assembled configuration, wherein each tank segment 102a-102d comprises a tank base portion 104a-104d, a tank sidewall portion 106a-106d and at least one peripheral joining edge 108a-108d extending along at least a portion of the tank base portion and sidewall portion, as described above. Arranging the plurality of tank segments 102a-102d into the assembled configuration comprises aligning the plurality of tank segments 102a-102d to abut along their peripheral joining edges 108a-108d. As described above, the specific alignment needed to arrange a plurality of tank segments into an assembled configuration may depend on the shape and number of tank segments 102a-102d within the system 100. In step 620, the method 600 comprises joining the plurality of tank segments 102a-102d together in the assembled configuration at the abutted peripheral edges 108a-108d to form the aquaculture tank. As described above, joining the plurality of tank segments 102a-102d together preferably involves the use a plurality of retaining members 140 to clamp adjacent tank segments together in the assembled configuration and then welding the adjacent tank segments together, while being clamped, in the assembled configuration at their abutted peripheral edges 108a-108d, preferably using the sealing means 120. In this case, step 620 preferably comprises inserting at least one first retaining member 141 into at least one opening 116a, 114a in each of the plurality of tank segments 102a-102d, and engaging pairs of first retaining members 141 that are inserted in respective adjacent tank segments either side of a join with at least one second retaining member 142 to exert a clamping force CF therebetween. In preferred embodiments, the plurality of tank segments 102a-102d are formed of a thermoplastic material and the sealing means 120 is an electrofusion means. In this case, step 620 comprises welding the adjacent tank segments together using an electrical heating element 120h applied along at least some of the peripheral joining edges 108a-108d of the tank segments 102a-102d. For example, this may comprise applying, using a heating apparatus 120a a heating current through the electrical heating elements 120h for a period of time to heat the surrounding material of the respective tank segments 102a-102d to or above a melting point of the material. Advantageously, when this electrofusion process is performed under the clamping force CF provided by the retaining member 140, rapid and efficient welding is possible. The above electrofusion process advantageously may provide a deep ‘internal’ weld substantially within the thickness of the wall of the tank segments 102a-102d, which may otherwise not be possible vis a conventional welding process using a handheld welding gun which provide more superficial ‘surface’ welds. The resulting internal weld promotes the strength, stability and liquid holding capacity of an assembled tank. However, it will be appreciated, that the internal weld produced by the electrofusion process may not extend completely through the thickness of the wall of the tank segments 102a-102d, e.g. to the inner surface of the base, and / or may potentially leave a small ridge or depression along the join / seam. As such, step 620 may further comprise a further (secondary) welding step of welding along the fused peripheral joining edges 108a-108d to fill or close any space therebetween, e.g. with a filler weld, using a welding tool, to provide a substantially smooth and continuous inner surface of the tank. As such, the purpose of the filler weld is not structural, but may reduce build-up of waste matter M at the seams. In some embodiments, the method further comprises removing the retaining members 141, 142 after the welding process is completed. In embodiments where the assembled tank comprises a drain opening D, the method 600 may comprise a step 630 of attaching a sump tank 180 to a drain opening D in the assembled tank. Preferably, the sump tank 180 comprises a circumferential flange 180f (or a similar protruding lip) extending laterally outwards from an open end of the sump tank 180, and step 630 comprises inserting the sump tank 180 into the drain opening D of the assembled aquaculture tank such that the flange 180f abuts and overlaps the tank base surface 704s around the drain opening D (i.e. a rim of the drain opening D). Preferably, step 630 comprises welding the flange 180f to the tank base surface 704s around a peripheral edge 1801 f of the flange 180f, e.g. with a fillet weld, to form a liquid tight seal therebetween. Established aquaculture tank assemblies, often suffer from a build-up of waste matter produced by the aquatic organisms being cultured. Build-up of waste matter in a tank causes the water quality to degrade and can lead to poisoning of the aquatic organisms being cultured and a corresponding low survival rate. As a result, waste matter must be regularly removed from the inside surfaces of the tank to prevent a build-up and maintain water quality. Conventional cleaning methods typically involve emptying the tank of all water and aquatic organisms to expose the inside surfaces of the tank, and manually cleaning the surfaces. Many aquatic organisms cannot survive out of water for long periods of time. The requirement for their tank to be cleaned can therefore restrict the type and species of organism which can be cultivated in this way. The use of secondary holding tanks also necessitates an aquaculture facility to have an excess of tanks above the minimum required for regular cultivation. Modular aquaculture tanks are particularly susceptible to this build-up of waste matter as, due to their construction, they typically comprise a multitude of seams along the inner surfaces of the tank resulting from the joining points of various constituent modular parts of the tank. Waste matter can be ‘snagged’ or become otherwise trapped along these seams more easily than in a non-modular tank formed of a single member or structure. The tank assembly produced or provided by the system 100 described above may provide a reduction in the prevalence of internal seams via the use of tank segments with integral base and sidewall portions. Furthermore, it may be beneficial to provide an improved cleaning method to reduce the build-up of waste matter in a (modular) aquaculture tank. As described above, embodiments of the system 100 that include the fluid propulsion unit 160 can provide a substantially self-cleaning tank assembly, which will now be described in more detail below. Figures 12(a) and 12(b) show schematic side and plan views of a self-cleaning aquaculture tank 700 for culturing marine or aquatic organisms according to an embodiment of the present disclosure. The tank 700 comprises at least one sidewall 706 and a base 704 defining a liquid holding volume. The tank 700 further comprises a drain 740 and a fluid propulsion unit 160 as described above. The tank 700 may be assembled from the system 100 described above, or provided as a standalone tank. It will be understood that any waste matter M held in suspension in the liquid of the tank 700 will, overtime, fall towards the surface 704s of the base 704 at least under the under the action of gravity. For this reason, figures 12(a) and 12(b) show a typical build-up of waste matter M along the base surface 704s of the tank 700. The drain 740 is in fluid communication with a drain opening D in the base 704 located at or near a centre of the tank 700 and is operable to remove liquid from the tank 700 at least under the action of gravity. Typically, the drain 740 is in fluid connection with an outlet or pipe system including one or more valves (not shown) such that liquid may be removed and directed away from the tank 700, as is known in the art. The fluid propulsion unit 160 is also located at or near a centre of the tank 700, preferably at or above the drain 740 as shown, and is operable to generate and direct a flow F1 of fluid away from the tank base surface 704s and towards a top surface of the liquid L in the tank 700. The upward flow F1 of fluid from the fluid propulsion unit 160 creates a low-pressure region in the vicinity of the fluid propulsion unit 160 which induces a radial flow of liquid F2 along the base surface 704s of the tank 700 towards the drain opening D, as shown in figures 12(a) and 12(b). As a result, any waste matter M entrained in the radial flow F2 will move towards the drain opening D of the drain 740 where it can collect and be removed. The fluid propulsion unit 160 thus provides a self-cleaning function. As shown in figure 12(a), as the flow of fluid F1 reaches the top surface of the liquid L, a further radial flow of liquid F3 along the surface of the liquid L directed away from the centre of the tank 700 is produced. The resulting combination offerees exerted on the liquid in the tank by the fluid propulsion unit 160 induces an overall circular liquid flow F4 on each side of the drain 740, as shown in figure 12(a). The shape of the overall circular liquid flow F4, when rotated about the centre of the tank 700 in three-dimensions, is thus substantially toroidal, such that the circular liquid flow F4 may form a toroidal current (or toroidal vortex) within the tank 700. It will be understood that a toroidal vortex causes liquid in the tank 700 to circulate, such that at the sidewall 706 liquid is forced downwards towards the base surface 704s and then liquid is forced along the base surface 704s towards the drain opening D. It will be understood that the toroidal vortex produced by the fluid propulsion unit 160 may advantageously gather together waste matter M dispersed in the liquid of the tank 700, encourage settling on the base surface 704s, and direct the waste matter M on the base surface 704s towards the drain opening D of the drain 740 for removal. This may increase the total fraction of and / or the rate of removal of waste matter M in the tank 700 which can be removed through the drain 740. Specifically, because the fluid propulsion unit 160 induces a flow of liquid / current ‘downwards’ towards the base surface 704s, it may be effective in removing at least partially buoyant pieces of waste matter which may, in the absence of the flow F1, naturally float ‘upwards’ towards the surface of the liquid L and hence away from the drain opening D. In preferred embodiments, the fluid propulsion unit 160 is an aeration device configured to generate and / or direct a flow F1 of gas into the liquid in the tank 700, such as air. As the gas is less dense than the liquid in the tank 700, the gas bubbles will naturally float upwards towards the surface of the liquid L generating a columnar flow of gas F1 and creating a corresponding upward liquid flow e.g. through drag or uplift. Advantageously, the aeration device 160 provides a dual function of aeration and self-cleaning, and may be more energy and cost efficient than other flow generating means, allowing the tank 700 to operate in a self-cleaning mode almost continuously. In other examples, the fluid propulsion unit 160 may alternatively comprise one or more liquid propulsion devices including, but not limited to: a propeller, an impeller, a pump-jet, a hydro-jet, a nozzle or any other similar device suitable to generate and direct a jet of liquid F1 away from the base surface 704s that induces a radial flow F2. The fluid propulsion unit 160 is preferably operated or configured to generate and direct a flow F1 of fluid (away from the tank base surface 704s and towards a top surface of the liquid L) at a predetermined flow rate. In preferred examples, the predetermined rate is at least 85 litres of fluid per minute. It will be understood that higher rates of flow F1 may increase the size and magnitude of the low-pressure region in the vicinity of the fluid propulsion unit 160 and thereby induce a relatively stronger radial flow of liquid F2 along the base surface 704s of the tank 700 towards the drain opening D. This may advantageously increase the total fraction of and / or the rate of removal of waste matter M in the tank 700 which can be removed through the drain 740. However, it will be understood that a stronger radial flow of liquid F2 may also disturb or otherwise hamper the culturing of aquatic organisms. For example, some aquatic organism may be more efficiently cultured in liquid with minimal turbulence. Hence, in practice the predetermined flow rate used for the fluid propulsion unit 160 will in general vary depending on the exact implementation of the tank 700. Figure 12(c) shows a schematic side view of an embodiment of the tank 700 further comprising a sump tank or settling portion 180 in fluid communication with the drain opening D and the drain 740. The setting portion 180 includes a set-back surface 180s (i.e. set-back from the base surface 704s) and provides a space for receiving and collecting waste matter M entrained in the radial flow F2. In general, the sump tank or settling portion 180 is configured to provide a region of the tank 700 in which waste matter M may collect, and can take any form that achieves this purpose. In the example of figure 12(c), the settling portion 180 is arranged as a separate sump tank or compartment connected to the drain opening D, such that waste matter M which enters the drain opening D passes into the sump tank 180 where it is retained and settles at least under the action of gravity. In other examples, a settling portion 180 can be integrated with or formed as part of the base 704 of the tank, for example as a depression, gulley, trench or ditch in the base surface 704s to provide a set-back surface 180s (not shown). Preferably, the drain 740 is located in the sump tank or settling portion 180 such that the waste matter M which collects in the sump tank 180 may be removed from the sump tank 180 by the drain 740. In the embodiment of figure 12(c), the drain 740 is located in the set-back surface 180s. In other examples, the drain 740 can be located in a side of the sump tank 180. In figure 12(c) the sump tank 180 is in fluid communication with the drain opening D and thus the liquid in the tank, such that liquid and waste matter M may freely flow into the sump tank 180. However, it will be understood that, typically aquatic organisms are not intended to enter the sump tank 180. As such, preferably the tank 700 is configured such that said aquatic organisms are separated from (and prevented from entering) the sump tank 180 via a mesh, grating or filter 770 arranged at, or enclosing, the drain opening D, as shown in figures 12(a) and 12(c). The mesh 770 may extend across the drain opening D or around the drain opening D (e.g., between the base 704 and the fluid propulsion unit 160 as shown). It will be understood that the desired internal dimensions of the mesh 770 (i.e. the maximum dimensions of objects to be allowed through the mesh 770) may depend on the aquatic organism being cultivated, where smaller organism being cultivated may require a finer mesh 770 such that said smaller organisms are prevented from entering the sump tank 180. In some embodiments, the tank 700 further comprises a drain valve operable to open and close the drain 740 and hence control the removal of liquid from the tank 700 or sump tank 180 through the drain 740. In some embodiments the drain 740 is connected to a pump operable to pump liquid out of the tank 700 through the drain 740. In some examples, e.g. where the fluid propulsion unit 160 comprises a liquid propulsion device, the fluid propulsion unit 160 further comprises a fluid intake located at or near the drain opening D. The fluid intake may be arranged to suction liquid into the fluid propulsion means 160 via the fluid intake to assist in producing the radial flow F2 towards the drain opening D. In some embodiments, the fluid propulsion unit 160 further comprises a propulsion valve operable to open and close the fluid propulsion unit 160 and hence to control the flow of liquid through the fluid propulsion unit 160. The tank 700 can be operated in a normal mode where the fluid propulsion unit 160 is not active and the drain 740 is closed, and a cleaning mode where the fluid propulsion unit 160 is active and the drain 740 is closed. Preferably, the tank 700 is operated in the cleaning mode substantially continuously for large portions of the day or periodically and / or according to a schedule e.g. to reduce energy and / or fluid consumption of the fluid propulsion unit 160. In some embodiments, the tank 700 is operated in the cleaning mode constantly such that the fluid propulsion unit 160 is active at all times. The tank 700 is further operable in a drain mode, wherein the drain 740 is opened for a short period of time to remove at least a portion, preferably all, of waste matter M collected, e.g. in the sump tank 180, during the cleaning mode (along with a small volume of liquid). The drain mode is preferably operated periodically. For example, the drain 740 may be opened periodically, e.g. 2 to 4 times a day (e.g. every 6-8 hours), and / or according to a predefined schedule, and for a duration of 1 minute or less to provide sufficient waste removal to maintain high liquid quality. However, it will be understood that the duration of time and / or frequency that the drain 740 is open may depend on the specific implementation and the desired level of liquid quality in the tank 700. For example, the duration may depend on the quantity of waste matter M and hence the size of the tank 700, where larger tanks may produce proportionally more waste matter M such that the drain 740 may be opened more frequently and / or for longer durations. The fluid propulsion unit 160 may remain active or be deactivated during the drain mode. Figures 12(a) and 12(c) show the fluid propulsion unit 160 supported above the drain opening D a supporting member 780 such as a platform.. However, in other examples the fluid propulsion unit 160 may instead be arranged at a side of the sump tank 180 or at least partially within the sump tank 180 (not shown). Figure 12(d) shows a schematic cross-sectional view of the fluid propulsion unit 160 supported above the drain opening D according to an example embodiment. The fluid propulsion unit 160 is supported on a platform 780 at a height H above the tank base surface 704s. The platform 780 has a width W1 that is greater than the corresponding width W2 of the fluid propulsion unit 160, such that the fluid propulsion unit 160 is substantially set back from a peripheral edge or rim 1801 of the platform 780, as shown. This serves to effectively separate liquid immediately adjacent fluid propulsion unit 160 from the drain opening 770, which in turn assists in preventing any turbulent flow induced by and immediately adjacent the fluid propulsion unit 160 disrupting the radial flow F2 and movement of waste matter M into the drain opening D. It may also help to prevent the fluid propulsion unit 160 from drawing liquid and collected waste matter M back out of the sump tank 180. For this purpose, the width W1 of the platform 780 is preferably also greater than the width W3 of the drain opening D so that the platform 780 extends over and beyond the rim of the drain opening D, as shown. Additionally or alternatively, a separate flange or rim may be attached to the platform 780 (not shown) to provide the / an increased width W1 and separate the liquid immediately adjacent fluid propulsion unit 160 from the drain opening 770. In one example, the width W2 (or maximum lateral dimension) of the fluid propulsion unit 160 is less then approximately two-thirds the width W2 (or minimum lateral dimension) of the platform 780. The height H of the platform 780 above the base 704 creates a gap or side opening through which liquid and waste matter M can access and enter the drain opening D. As described above, a mesh or filter 770 can be provided in the gap between the platform 780 and the base 704 to prevent aquatic organisms being cultivated in the tank 700 entering the drain opening D and / or sump tank 180. In some cases, the height H may be selected to be sufficiently small (e.g. smaller than the dimensions of said aquatic organisms) to prevent / inhibit the aquatic organisms entering the drain opening D whilst permitting the flow of waste matter M into the drain opening D. In addition, it will be appreciated that reducing the height H can increase the velocity of the radial flow F2 into the drain opening D, the suction effect and thus the efficiency of the waste matter M collection. In preferred examples, the height H is equal to or less than 10 cm, and more preferably equal to or less than 5 cm. The platform 780 is supported at the height H by a supporting member 790 which extends from a wall of the sump tank 180, e.g. the set-back surface 180s. In this example, the supporting member is a substantially rod-like member, which may optionally be hollow to allow a fluid (gas) source line to pass therethrough and to the fluid propulsion unit 160. The platform 780 may be fixed to a distal end 791 of the supporting member 790 such that the height H is fixed and determined by the length of the supporting member 790, preferably predetermined for a given tank 700 configuration. Alternatively, in some embodiments, the platform 780 and / or supporting member 790 may provide means for adjusting the height H, e.g. to control and optimise the flow F2 and / or filtering properties. It will be appreciated that height adjustment may be implemented in multiple ways. In the example of figure 12(d), the distal end 791 of the supporting member 790 is threaded and platform 780 comprise a threaded opening (not shown) such that the platform 780 can ‘screw on’ to the supporting member 790 by a variable amount to lower (or raise) the platform 780 towards (or away from) the tank base surface 704s thereby reducing (or increasing) the height H. In other examples, the length of supporting member 790 may itself be adjustable, e.g. by a telescopic mechanism. In the example of figure 12(d), the sump tank 180 is a separate component which is inserted into the drain opening D of the tank during assembly (e.g. where the tank 700 is formed from the system 100, the sump tank 180 is inserted after the plurality of tank segments are joined). As shown, the sump tank 180 comprises a flange 180f (or a similar protruding lip) which extends out from the sump tank 180 parallel to the tank base surface 704s and is arranged to overlap and abut the tank base surface 704s (at a rim of the drain opening D) to form a liquid tight seal therebetween. Preferably, the sump tank 180 is welded to the base 704 at a peripheral edge 1081 f of the flange 180f. Such a weld may be referred to as a fillet weld. It will be understood this may improve the tightness or durability of the seal. Figure 12(e) shows a schematic perspective view of the fluid propulsion unit 160 supported above the drain opening D according to an example embodiment Like in figure 12(d), the fluid propulsion unit 160 is supported on a platform 780 at a height H above the tank base surface 704s, however, this case, the platform 780 is supported by a plurality of supporting members 790 which extend from the base 704 of the tank 700 around the drain opening D. In this way, the plurality of supporting members 795 act as ‘legs’ to attach the platform 780 to the tank base surface 704s and support the platform 780 above the drain opening 770. In such an embodiment, any or all of the plurality of supporting members 790 may have a fixed (predetermined) or adjustable length such that height H may be optimised, as described above. Figure 13 shows a schematic flow diagram of a method 800 ofcleaning the aquaculture tank 700 according to an embodiment of the disclosure. In step 810, the method 800 comprises generating, using a fluid propulsion unit 160 located at or adjacent a drain opening in a base 704 of the aquaculture tank 700, a flow F1 of fluid directed away from the base 704 of the tank 700 to thereby induce a flow F2 of liquid along the base 704 towards to the drain opening D to direct waste matter M entrained in the flow F2 towards the drain opening D. The drain opening D is preferably located at the centre of the tank 700, and the flow F2 is a radial flow F2. In step 820, the method 800 comprises collecting waste matter M entrained in the flow F2 at the drain opening D. In step 820, collecting waste matter M preferably comprises collecting the waste matter M in a sump tank or settling portion 180 coupled to the drain opening D, wherein the sump tank or settling portion 180 provides a set-back surface 180s from the tank base 704. In step 830, the method 800 comprises opening a drain 740 in fluid communication with the drain opening D to remove collected waste matter M from the tank 700. Opening the drain 740 may comprise opening a drain valve. Step 830 may comprise opening the drain 740 periodically or according to a predefined schedule. Step 810 may comprise activating or operating the fluid propulsion unit 160 to generate the flow F1 of fluid directed away from a base surface 704s of the tank 700. Activating may comprise operating a control valve or switch. The fluid propulsion unit 160 is preferably an aeration device and is activated or operated continuously for a period of time, preferably constantly during operation or use of the tank 700, and / or periodically. It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. Any feature of the system or tank segment as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure. Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

1. A tank segment for an aquaculture tank assembly, comprising:a tank base portion;a tank sidewall portion; andat least one peripheral joining edge extending along at least a portion of the tank base portion and the tank sidewall portion;wherein the tank segment is configured to abut and be joined at its at least one peripheral joining edge to at least one other corresponding tank segment to form at least part of an aquaculture tank assembly.

2. The tank segment of claim 1, wherein the tank base portion extends from the tank sidewall portion and tapers in lateral width towards a centre of the aquaculture tank assembly, and optionally of preferably, wherein the tank segment is a quadrant of the aquaculture tank assembly.

3. The tank segment of claim 1 or 2, wherein the tank sidewall portion extends from the tank base portion to a rim of the aquaculture tank assembly.

4. The tank segment of any preceding claim, wherein the tank segment comprises at least one load bearing support portion; optionally or preferably, wherein the at least one load bearing support portion extends from an underside of, and / or is integrated with, the tank base portion.

5. The tank segment of any preceding claim, wherein the tank base portion and the tank sidewall portion form or provide a continuous inner surface of the aquaculture tank assembly; and / or form part of a respective base and sidewall of the aquaculture tank assembly.

6. The tank segment of any preceding claim, wherein the tank segment is a unitary structure, and / or is formed of a unitary piece of material.

7. The tank segment of any preceding claim, wherein the tank segment is formed of orcomprises a thermoplastic material.

8. The tank segment of any preceding claim, wherein the tank base portion is configured to form at least a portion of a drain opening in a base of the aquaculture tank assembly.

9. The tank segment of any preceding claim, further comprising at least one opening to receive at least a portion of a respective first retaining member for clamping the tank segment to another corresponding tank segment in an assembled configuration.

10. The tank segment of claim 9, wherein the at least one opening includes at least one opening in the tank sidewall portion and at least one opening in the tank base portion.

11. The tank segment of claim 9 or 10, wherein the at least one opening is located adjacent to, and extends in a direction substantially parallel to, at least a portion of the at least one peripheral joining edge; and optionally or preferably,wherein the at least one opening includes at least one opening extending at least partially through and along the tank sidewall portion.

12. The tank segment of any of claims 9 to 11, wherein the tank segment includes first and second peripheral joining edges extending at least partially along respective first and second lateral sides of the tank sidewall portion and tank base portion, and wherein the at least one opening in each tank segment includes:a first opening located adjacent to, and extending through at least part of the tank sidewall portion in a direction substantially parallel to, the first peripheral joining edge; anda second opening located adjacent to, and extending through at least part of the tank sidewall portion in a direction substantially parallel to, the second peripheral joining edge.

13. The tank segment of any of claims 9 to 12, wherein the at least one opening extends through and along the tank segment.

14. The tank segment of any preceding claim, further comprising a sealing means attached along at least a portion of the at least one peripheral joining edge for sealing the tank segment to another corresponding tank segment; and optionally or preferably,wherein the sealing means comprises one or more elongate electrical heating elements operable to heat the surrounding material of the tank segment to thereby weld the tank segment to another corresponding tank segment at their respective peripheral edges.

15. A system for forming an aquaculture tank assembly, comprising:a plurality of tank segments as defined by any of claims 1 to 14; wherein the plurality of tank segments are configured to abut along their respective peripheral joining edges in an assembled configuration and be joined at their respective peripheral joining edges to form an aquaculture tank assembly.

16. The system of claim 15, wherein the plurality of tank segments are configured to be arranged, in the assembled configuration, circumferentially about a centre of the assembled aquaculture tank, and preferably symmetrically about a centre of the aquaculture tank assembly.

17. The system of claim 15 or 16, wherein the plurality of tank segments are substantially identical.

18. The system of claim 15, 16 or 17, wherein the tank segments are configured to form a freestanding aquaculture tank assembly.

19. The system of any claims 15 to 18, further comprising a plurality of retaining members, wherein the plurality of retaining members are operable to clamp together the plurality of tank segments in the assembled configuration; and optionally or preferably,wherein at least one of the plurality of retaining members are configured to be arranged parallel to at least a portion of the at least one of the peripheral joining edge of each respective tank segment.

20. The system of claim 19, wherein the plurality of retaining members include a plurality of pairs of first retaining members mounted or mountable to the plurality of tank segments, and a plurality of second retaining members operable to engage the respective pairs of first retaining members and exert a clamping force therebetween to thereby clamp together the plurality of tank segments in the assembled configuration; and optionally or preferably,wherein the plurality of second retaining members are removably attachable to the plurality of pairs of first retaining members.

21. The system of claim 20, wherein each first retaining member of a pair is mounted or mountable adjacent a peripheral joining edge of a different one of the plurality of tank segments so as to provide, when engaged by a respective second retaining member, a clamping force between adjacent tank segments in the assembled configuration.

22. The system of claim 20 or 21, wherein the first retaining members are configured to be arranged as internal or integral components of the plurality of tanks segments.

23. The system of any of claims 20 to 22, wherein each tank segment further comprises at least one opening for receiving at least a portion of a first retaining member of a respective pair of first retaining members, and wherein the plurality of pairs of first retaining members are insertable into the respective openings of the plurality of tank segments.

24. The system of claim 23, wherein the first retaining members are insertable into the respective openings in a direction substantially perpendicular to the direction of the clamping force; and / or, wherein the at least one opening in each tank segment includes at least one opening in the tank sidewall portion and at least one opening in the tank base portion.

25. The system of claim 23 or 24, wherein the at least one opening in each tank segment is located adjacent to, and extends in a direction substantially parallel to, at least a portion of the at least one peripheral joining edge; and optionally or preferably,wherein the at least one opening includes at least one opening extending at least partially through and along the tank sidewall portion.

26. The system of any of claims 23 to 25, wherein each tank segment includes first and second peripheral joining edges extending along at least a portion of respective first and second lateral sides of the tank sidewall portion and tank base portion, and wherein the at least one opening in each tank segment includes:a first opening located adjacent to, and extending through at least part of the tank sidewall portion in a direction substantially parallel to, the first peripheral joining edge; anda second opening located adjacent to, and extending through at least part of the tank sidewall portion in a direction substantially parallel to, the second peripheral joining edge; and optionally or preferably, wherein the first and second openings extend through the respective tank sidewall portion and tank base portion.

27. The system of any of claims 15 to 26, further comprising a sealing means attachable along at least some of the peripheral joining edges of the plurality of tank segments for sealing adjacent tank segments at their respective peripheral joining edges in the assembled configuration.

28. The system of claim 27, wherein the sealing means comprises one or more elongate electrical heating elements operable to heat the surrounding material of the respective tank segments to thereby weld adjacent tank segments together at their respective peripheral edges and form the tank assembly.

29. The system of any of claims 15 to 28, wherein the aquaculture tank assembly comprises a drain opening located, preferably centrally, in a base of the aquaculture tank assembly, and wherein the tank base portion of at least one tank segment of the plurality of tank segments is configured to form at least a portion of the drain opening of the aquaculture tank assembly when assembled; and optionally or preferably, wherein each tank base portion of the plurality of tank segments comprises a portion of the drain opening.

30. The system of claim 29, further comprising a fluid propulsion unit mountable at or near the drain opening of the aquaculture tank assembly and operable, in use, to output a flow of fluid directed away from the base of the aquaculture tank assembly to thereby induce a radial flow of liquid in the aquaculture tank assembly along the base towards the drain opening; and optionally or preferably,wherein the fluid propulsion unit is configured, in use, to induce a toroidal vortex flow within the liquid in the aquaculture tank assembly.

31. The system of claim 30, wherein the fluid propulsion unit comprises an aeration device.

32. The system of claim 30 or 31, further comprising a sump tank or settling portionattachable to the drain opening, wherein the sump tank or settling portion provides a set-back surface for collecting debris entrained in the radial flow.

33. A method of assembling an aquaculture tank assembly, comprising the steps of: arranging a plurality of tank segments into an assembled configuration, wherein each tank segment comprises a tank base portion, a tank sidewall portion and at least one peripheral joining edge extending along at least a portion of the tank base portion and the tank sidewall portion, and wherein arranging comprises aligning the plurality of tank segments to abut along their respective peripheral joining edges; andjoining the plurality of tank segments together in the assembled configuration at the abutted peripheral edges to form the aquaculture tank assembly.

34. The method of claim 33, wherein joining comprises welding adjacent tank segments within the plurality of tank segments together at their respective abutted peripheral edges; and optionally or preferably,wherein the plurality of tank segments are formed of a thermoplastic material and welding comprises using an electrical heating element applied along at least some of the peripheral joining edges of the tank segments; and further preferably,wherein welding comprises applying a heating current through the heating elements for a period of time to heat the surrounding material of the respective tank segments to or above a melting point of the material.

35. The method of claim 33 or 34, further comprising the steps of:prior to joining the plurality of tank segments, clamping adjacent tank segments together in the assembled configuration using a plurality of retaining members; and optionally or preferably,wherein clamping comprises the steps of:inserting at least one first retaining member of the plurality of retaining members into at least one respective opening in each of the plurality of tank segments, andengaging pairs of the first retaining members that are inserted in respective adjacent tank segments with at least one second retaining member of the plurality of retaining members to exert a clamping force between each pair of the first retaining members.

36. The method of claim 33, 34 or 35, further comprising attaching a sump tank to a drain opening in a base of the tank assembly; and optionally or preferably,wherein the sump tank comprises a circumferential flange extending laterally outwards from an open end of the sump tank, and attaching comprises inserting the sump tank into the drain opening of the aquaculture tank assembly such that the flange abuts and overlaps the base around the drain opening; and preferably sealing the flange to the base.

37. A self-cleaning aquaculture tank, comprising:a tank with a base and at least one sidewall;a drain opening in the base for removal of liquid from the tank;a fluid propulsion unit arranged at or near to the drain opening; andwherein the fluid propulsion unit is configured to generate a flow of fluid directed away from the base and thereby induce a flow of liquid along the base towards to the drain opening for directing waste matter entrained in the flow of liquid towards the drain opening.

38. The tank of claim 37, wherein the fluid propulsion unit further induces a toroidal vortex within liquid in the tank.

39. The tank of claim 37 or 38, wherein the drain opening is located centrally in the base of the tank, and preferably wherein the drain opening and the fluid propulsion unit are substantially co-located.

40. The tank of any of claims 37 to 39, wherein the fluid propulsion unit comprises an aeration device.

41. The tank of claim any of claims 37 to 40, further comprising a sump tank or settling portion in fluid communication with the drain opening, wherein the sump tank or settling portion includes a set-back surface for collecting debris entrained in the radial flow, and preferably wherein the tank comprises a drain located in sump tank.

42. A method of cleaning an aquaculture tank, comprising the steps of:generating, using a fluid propulsion unit located adjacent a drain opening in a base of the aquaculture tank, a flow of fluid directed away from a base of the tank to thereby induce a flow ofliquid along the base towards to the drain opening to direct waste matter entrained in the flow towards the drain opening; andcollecting waste matter entrained in the flow at the drain opening.5 43. The method of claim 42, further comprising opening a drain in fluid communication with the drain opening to remove collected waste matter from the tank.

44. The method of claim 42 or 43, wherein the fluid propulsion unit comprises an aeration device.

045. The method of claim 42, 43 or 44, wherein collecting waste matter comprises collecting the waste matter in a sump tank or settling portion in fluid communication with the drain opening.Application No: GB2411629.5Examiner: Cassandra FraserClaims searched: 1-36Date of search: 25 February 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1, 3-9, 14, 15, 18, 19, 27, 29, 33, 35 KR 20200078204 A (INDUSTRY-ACADEMIC COOPERATION FOUNDATION GYEONGSANG NATIONAL UNIV). See figures and description. X 1-8, 14- 18, 27, 29, 33, 34 CN 210094381 U (BIOLOGICAL TECH INSTITUTE OF FUJIAN ACADEMY OF AGRICULTURAL SCIENCES). See figures 2, 4 and 7 and description. X 1-6, 8, 9, 14-22, 27, 29, 33, 35 CN 113197148 A (MCC CHINA COMMUNICATIONS INVESTMENT SHANZHU CHENGDU PREFABRICATED BUILDING TECH DEVELOPMENT CO LTD). See figures and description. X 1, 3-9, 14, 15, 18-21, 27, 29, 33 JP 2018011581 A (EARTHRING CO LTD). See figures and description. X 1-5, 8-10, 14-23, 27, 29, 33 US 8813684 B2 (BUCHANAN). See figures 3-5 and 7 and the description.Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority' date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From AO IK 0063 / 00 01 / 01 / 2017

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