Aquaculture System and Method

Abstract

Aquaculture system with a tank 102 having a culturing section 106. The tank has at least one integrated spray nozzle 110 arranged to direct a jet of liquid along at least a portion of the base 108 for

Description

Technical Field The disclosure relates generally to an aquaculture system for culturing marine or aquatic organisms, particularly but not exclusively to a system including a tank with a spray-based cleaning system. The disclosure also relates to a method of operating an aquaculture system. Background Established aquaculture systems involving tanks such as raceway tanks suffer from a buildup 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. In raceway tanks in particular, waste matter tends to build up preferentially at the outlet end of the tank, resulting in higher water quality near the inlet end and poorer quality water near the outlet. 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. For the duration of this cleaning time, said aquatic organisms must either be left outside of a tank and exposed in the air, or temporarily placed in a secondary holding or other aquaculture tank, for which both options can present problems. 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. Running tanks purely as temporary holding tanks increases capital and operational costs of the aquaculture facility, and transferring organisms from a main tank to a holding tank must also be done quickly to minimise their time out of water. The necessary logistical steps to this process also further increase operational costs and can lead to accidental damage to the aquatic organisms during transit leading to mortality and additional cost to the operation. Traditional cleaning processes are therefore labour intensive, time consuming, and present a significant overhead for an aquaculture facility. Further, the requirement for operator supervision also limits the times at which cleaning can be performed. For these reasons (and others including operator error and health and safety considerations), cleaning of typical aquaculture systems is typically performed less frequently than required for maintaining optimum water quality resulting in sub-optimal survival rates. Aspects and embodiments of the present disclosure have been devised with the aim of improving the process of cleaning and maintaining aquaculture systems. Summary According to a first aspect of the disclosure, there is provided an aquaculture system for culturing marine or aquatic organisms. The system comprises a tank with a base, the tank including at least one spray nozzle arranged to direct a jet of liquid along or towards at least a portion of the base for cleaning the at least a portion of the base. The system preferably further comprises one or more valves, including at least one nozzle valve operable to control a flow of liquid to said at least one spray nozzle. The tank preferably has a culturing section, whereby said base forms part of the culturing section. The aquaculture system of the present disclosure represents a significant advancement in the art by providing an improved means for cleaning the tank and maintaining high water quality, which in turn improves yield and survival rate of the cultured organisms. Specifically, spray nozzle(s) are used to direct a high velocity jet or sheet of liquid along the base of the tank to dislodge waste material and effectively clean the base surface. This cleaning process can be performed manually by an operator controlling the valves, or fully automated through the use of a controller, in either case the system can substantially reduce the time, labour and costs of cleaning the tank and improve the operational efficiency of the system compared to traditional manually controlled cleaning processes and systems. Further, improved cleaning means allows the tank to be cleaned more quickly and frequently than conventional manual cleaning approaches, particularly when automated. The overall effect of the system is that the average water quality and hygiene of the tank can be maintained at a higher level over time in general operation, which is advantageous for the culture of species that can withstand regular short exposure to air (improving the yield and survival rate). The system may be suitable for culturing any water dwelling organism, including but not limited to species of echinoderms, such as sea urchins, sea stars etc., molluscs (e.g. abalone, whelks,), crustaceans including lobsters, crabs, invertebrates and / or vertebrates. The culturing section of the tank is configured to hold a volume of liquid for culturing marine or aquatic organisms therein. It is the part of the tank in which marine or aquatic organisms are held and cultured. The culturing section 106 includes a base which in turn includes at least a portion of the bottom surface of the tank 102. Depending on the cross-sectional shape of the tank 102, the base may also include a portion of the at least one side surface of the tank. The base can also be referred to herein as the base section or base surface. The tank preferably further comprises a drain provided at or near the base of the culturing section for removing liquid from the culturing section. The drain is preferably an opening or a conduit connected to an opening in the base of the tank, but may instead be part of a pumping arrangement (see below). The tank preferably includes one or more side walls which, together with the base provide a liquid holding body. The nozzles may be configured to produce and direct a jet of liquid along or towards at least a portion of the base to dislodge and remove waste material on the base of the culturing section. Directing the jet of liquid along the base means that water pressure may simultaneously be used to dislodge waste from the base and to push the resulting waste in solution towards the drain. The nozzles are preferably integrated with the tank. Integrating the nozzles within the tank may provide easier installation of the system and also may allow easier servicing of the nozzles. The system is preferably configured to operate in a cleaning mode whereby liquid is removed or drained from the culturing section through the drain, and the at least one nozzle valve is open or operated to provide a flow of liquid to the at least one spray nozzle for cleaning the at least a portion of the base surface of the culturing section. The at least one spray nozzle is configured to produce or generate a jet of liquid in response to receiving said flow of liquid. The tank may be any device suitable for retaining a volume liquid in which marine or aquatic organisms can be cultured. The tank may be constructed from any suitable non-porous material, such as a metal and / or plastic-based material, as is known in the art. The tank may be configured to be substantially free standing, mounted in a frame, or at least partially located below ground. Preferably, the tank is a raceway or raceway-style tank. A raceway tank may be defined as a substantially elongate longitudinal channel-shaped or rectangular-shaped tank or basin (i.e. having a length greater than its width) which is configured as a flow-through system, having an inlet at one end of the channel and an outlet at the opposite end of the channel. In normal operation, liquid is continuously provided to the raceway tank at the inlet to provide a continuous flow along the channel and into the outlet (through displacement) and to maintain a predefined liquid level and a required water quality. Preferably, the tank further comprises an inlet at or near a first end of the culturing section operable to supply an inlet flow of liquid into the culturing section; and an outlet at or near a second end of the culturing section to receive an outlet flow and maintain a predefined liquid level in the culturing section. Preferably, the outlet is or comprises a weir assembly. The weir assembly preferably comprises a low barrier or dam over the top of which flows the outlet flow to thereby maintain a predefined liquid level in the culturing section. The barrier of the weir preferably extends across a width of the culturing section. The barrier of the weir assembly may form, or be formed by, a sidewall of the culturing section of the tank. The weir assembly may further comprise an outlet on a downstream side of the barrier for removing or draining liquid from the tank that has flowed over the barrier. The system is preferably configured to operate in a normal mode whereby an inlet flow of liquid is supplied through the inlet to thereby cause an outlet flow of liquid into the outlet, or weir assembly (e.g. by liquid displacement). The one or more valves preferably further include an inlet valve operable to control the inlet flow of liquid through the inlet. The inlet valve is substantially open in the normal mode. Optionally or preferably the inlet valve is closed in the cleaning mode. The one or more valves preferably further include a drain valve operable to control the removal of liquid from the culturing section through the drain. The drain valve is preferably substantially open in the cleaning mode and preferably closed in the normal mode. The system preferably further comprises a pumping arrangement in communication with the drain and operable to pump liquid out of the tank through the drain when the system is in the cleaning mode. Alternatively or additionally, the pumping arrangement may instead be arranged to pump or draw liquid directly out of the culturing section of the tank in addition to or instead of liquid being removed through the drain via gravity. In this case, instead of the drain being an opening or connected to an opening in the base, the drain may additionally or instead be part of the pumping arrangement (e.g. the drain may comprise a hose or pipe that extends from the pumping arrangement to the base of the culturing section for pumping the liquid from the tank). The pumping arrangement may be activated in the cleaning mode and deactivated in the normal mode. Optionally or preferably, the pumping arrangement is or comprises a mechanical pump, or a syphon pump. A pumping arrangement may increase the speed at which water is drained from the tank and thereby reduce the time needed to switch from the normal mode to the cleaning mode of operation of the system. Increasing the draining speed may also reduce the overall time the organisms are exposed to air during the cleaning cycle. The system preferably further comprises a controller for controlling the operation of the system. The controller is preferably configured to control the one or more valves to thereby control an operating mode of the system. The controller is preferably further configured to control the pumping arrangement (where present). Use of a controller may allow the operation of the system, in particular the cleaning, to be automated thereby reducing the amount of operator input and labour requirements to operate and maintain the system. The controller is preferably further configured to operate or control the system to operate a cleaning cycle in which the system is switched or transitioned from the normal mode to the cleaning mode for a predefined period of time (and then switched or transitioned back to the normal mode). Optionally or preferably, the cleaning cycle is operated or executed periodically, or according to a predefined schedule. Operating the system in a cleaning cycle that is executed periodically or according to a predefined schedule may allow the cleaning cycle to be affected without direct human intervention and thus may be able to be run more frequently and during hours when human supervision is not available or when the system is situated in remote locations. The one or more valves may be configured to actuate or operate in response to a control signal received from the controller. The controller may be in wired or wireless communication with the one or more valves. The controller may be configured to transmit a control signal to the one or more valves to thereby control an operational state of the respective valves. The operational state of the one or more valves may include an open state, a closed state and optionally one or more partially open states. Use of wireless communication within the system may reduce installation costs of the system by removing the need to lay cables / wires to each valve of the system. The controller is preferably programmable. The controller preferably comprises a processor and a memory configured to store instructions that, when executed by the processor, cause the controller to control the operation of the system. The memory may store the one or more of: the schedule, timing data determining the valve timings, time period for operating in the cleaning mode, periodicity, frequency or timing of the cleaning cycle. The controller may further be in wireless communication with a remote device for receiving one or more control signals or inputs from the remote device. The controller may be configured to change an operation mode, or one or more of the schedule, timing data determining the valve timings, time period for operating in the cleaning mode, periodicity, frequency or timing of the cleaning cycle, in response to the control signal or input. For example, the controller may comprise a wireless communication module. This may allow the controller and the operation of the system to be controlled remotely. Preferably the at least one spray nozzle comprises a plurality of spray nozzles. Preferably, at least some of the plurality of spray nozzles are distributed along a transverse direction of the culturing section, further preferably at or near the inlet end of the culturing section. The at least some of the plurality of spray nozzles may be distributed across the width of the culturing section at the at or near the inlet end of the culturing section. In this way, the nozzles can generate a high velocity sheet of liquid that can dislodge and clean any waste material on the base of the culturing section. Arranging the spray nozzles across a width of the culturing section may ensure that the high velocity sheet of liquid completely or substantially covers the base of the culturing section such that a greater fraction of the waste in the tank may be pushed towards the drain. Alternatively or additionally, at least some of the plurality of spray nozzles may be distributed along a longitudinal direction of the culturing section, e.g. along substantially an entire length of the culturing section. Arranging the spray nozzles along a longitudinal direction of the culturing section may improve the effectiveness of the cleaning, e.g. by helping the high velocity sheet of liquid to be maintained along length of the culturing section, and to be directed to every part of the culturing section. The system preferably further comprises a tray removably mountable to the tank. The tray is preferably configured to support or retain aquatic organisms within the culturing section in a region spaced apart from the base of the culturing section. The tray may have a base and sides, wherein the base is spaced apart from the base of the tank when mounted to the tank. Arranging the tray to be removably mountable to the tank may allow groups of aquatic organisms to be placed into or removed from the tank without draining any liquid from the tank and thereby may reduce time to harvest said aquatic animals. Mounting the tray such that its base is spaced apart from the base of the tank may allow the high velocity sheet of liquid to run freely along the base without passing through, into or around, the tray and thereby may allow waste to be pushed towards the drain and the tank be cleaned without interfering with the aquatic organisms in the tray. Preferably, the tank comprises a sidewall (a longitudinal sidewall in the case of a raceway tank) and the tray is removably mountable to the (longitudinal) sidewall. Mounting the trays to the sidewall may allow trays to be fully suspended above the base of the tank without the use of legs or the like which may interfere with the cleaning. This may in turn also prevent the tray being dislodged or moving during the cleaning cycle and hence may reduce damage or disruption to the aquatic organisms. Preferably, the base of the culturing section comprises a well or depression of increased depth (or a portion of increased depth), and wherein the drain is positioned at or in the drainage portion. Preferably, the well or depression is located at or near the outlet end of the tank. Use of a well or depression may cause waste to preferentially funnel toward or to gather at or near the drain, and thus may increase the fraction of waste removed during the cleaning cycle. Furthermore, use of a well may advantageously prevent backflow of liquid (potentially including waste material) towards the inlet end which would otherwise take more time to flush into the drain and thereby may improve the overall cleaning and drainage of liquid in the cleaning mode. The well may have a cross-sectional shape suitable for trapping liquid. Preferably, the well has a substantially rectangular cross-section with a side portion and a base portion that together provide a step down and / or abrupt change in depth of the culturing section. The side portion is preferably arranged substantially perpendicular to the main or an adjacent portion of the base, or to a flow of liquid produced from the nozzles, so as to assist in trapping liquid and preventing backflow. The side portion and / or base portion may be substantially flat, sloped or curved. Preferably, at least one of the at least one spray nozzle is arranged to direct a jet of liquid towards the drain, and / or towards the outlet end of the tank. The system may further comprise an aeration system for providing air or another suitable gas to liquid in the culturing section. The aeration system may be or comprise one or more porous or perforated aeration lines. The one or more aeration lines may extend at least partially along the length and / or width of the base. Certain species of aquatic organisms (including some species of echinoderms) may benefit when a gas is dispersed into the liquid in the culturing section, thus the use of an aeration system may allow gas to be dispersed evenly through the liquid in the culturing system and thereby may improve the survival rate, quality or quantity of the aquatic organisms being cultivated. The system preferably further comprises a reservoir in fluid communication with the inlet for supplying an inlet flow of liquid to the inlet. The system preferably further comprises a filtration system in fluid communication with the drain and the reservoir, wherein the filtration system is configured to filter at least a portion of liquid removed from the culturing section through the drain and preferably return filtered liquid to the reservoir. Reusing the liquid removed from the culturing section may reduce overall liquid consumption of the system and thereby may reduce the operational costs and the environmental impact of the system.. The system may further comprise an inlet pump and a nozzle pump for producing the liquid flow to the inlet and nozzles at a respective inlet flow rate and nozzle flow rate. Preferably, the nozzle flow rate is substantially greater than the inlet flow rate. The reservoir may further supply a nozzle flow to the nozzles. The tank preferably includes a plurality of internal surfaces including at least one side surface and a bottom or base surface which forms part of the base. The tank may have a substantially rectangular cross-section with a flat base, such that the at least one side surface and bottom surface are substantially perpendicular to one another and comprise substantially planar surfaces. Alternatively, the sides and bottom surface may instead form curved or irregular surfaces, or which may be combined to form one singular flush surface, such that there is no clear distinction between the side and bottom surfaces. According to a second aspect of the disclosure, there is provided a method for operating an aquaculture system for culturing marine or aquatic organisms. The aquaculture system includes a tank comprising at least one spray nozzle. Preferably the system comprises one or more valves including at least one nozzle valve in fluid communication with the at least one spray nozzle, operable to control a flow of liquid to said at least one spray nozzle. Preferably the at least one spray nozzle is directed at a portion of the inner surface of the tank. Preferably the portion of the inner surface is adjacent to aquatic organisms being cultured in the aquaculture system. The aquaculture system may be an aquaculture system as defined in the first aspect. The method comprises using the at least one spray nozzle to direct a jet of liquid at the inner surface of the tank in order to clean the inner surface of the tank. Alternatively or additionally, the method comprises operating the one or more valves including the at least one nozzle valve to cause a jet of liquid to be directed along at least a portion of the inner surface of the tank by the at least one spray nozzle to clean the at least a portion of the inner surface of the tank. The tank may comprise a culturing section with a base, the base having an inner surface at which at least one spray nozzle is arranged to direct the jet of liquid. The method preferably further comprises operating a cleaning cycle. The cleaning cycle comprises: emptying liquid from the culturing section of the tank; operating the at least one nozzle valve to cause a jet of liquid to be directed along at least a portion of the base of the culturing section by the at least one spray nozzle for a predefined period of time; and filling the culturing section with liquid. Optionally or preferably, operating the at least one nozzle valve comprises opening the at least one nozzle valve for the predefined period of time. Preferably the cleaning cycle is repeatable. Preferably, the system comprises a drain provided at or near the base of the culturing section for removing liquid from the culturing section, and the one or more valves include a drain valve to control the removal of liquid from the culturing section through the drain. In this case, emptying liquid from the culturing section preferably comprises opening the drain valve to empty liquid from the culturing section through the drain; and filling the culturing section with liquid comprises closing the drain valve. The method may further comprise operating a pumping arrangement (of the system) in communication with the drain to pump liquid out of the culturing section through the drain. The method may further comprise operating the system in a normal mode, comprising: supplying an inlet flow of liquid to the culturing section of the tank; and removing an outlet flow of liquid from the culturing section to maintain a predefined liquid level in the culturing section. The inlet flow may be provided at a first end of the culturing section / tank, and the outlet flow may be removed at a second end of the culturing section / tank. Optionally or preferably, supplying the inlet flow produces a continuous flow of liquid through the culturing section of the tank. The system preferably includes an inlet valve to control the inlet flow of liquid to the culturing section. Optionally or preferably, operating the system in a normal mode further comprises opening the inlet valve or maintaining the inlet valve in an open state, and / or closing the drain valve or maintaining the drain valve in a closed state. Operating the cleaning cycle may further comprise stopping the inlet flow; emptying liquid from the culturing section; operating the at least one nozzle valve to cause a jet of liquid to be directed along at least a portion of the base of the culturing section by the at least one spray nozzle for a predefined period of time; and supplying the inlet flow of liquid to the culturing section to fill the culturing section with liquid to the predefined liquid level. Stopping the inlet flow may comprise closing the inlet valve and filling the culturing section with liquid to the predefined liquid level may comprise opening the inlet valve. Optionally or preferably, operating the cleaning cycle further comprises closing the inlet valve for a predetermined period of time. The system preferably further comprises a controller configured to control one or more valves to thereby control the operation of the system. In this case, the method preferably further comprises using the controller to operate the one or more valves, and optionally or preferably, the pumping arrangement. Optionally or preferably, the method may comprise using the controller to change an operating mode of the system. The method may further comprise filtering the liquid emptied or removed from the culturing section of the tank. Preferably the method further comprises storing the filtered liquid in a reservoir and using the stored filtered liquid to fill the culturing section and / or to supply the inflow of liquid to the culturing section. Any system feature 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, device 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 methods, system and device 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. The disclosure will now be described, by way of example, with reference to the accompanying drawings. 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 an aquaculture system as described herein; Figure 2 is a schematic diagram of an aquaculture system according to another example; Figures 3(a) and 3(b) show schematic cross-sectional and plan view diagrams of an example raceway tank for the aquaculture system of figures 1 or 2 in a normal mode of operation; Figure 4 shows a schematic cross-sectional diagram of the raceway tank of figure 3 in a cleaning mode of operation; Figure 5 shows a schematic diagram of example valve timing for operating a cleaning cycle in the aquaculture system of figures 1 or 2; Figure 6 shows a schematic diagram of operating a cleaning cycle periodically over time; Figures 7(a) to 7(c) show schematic diagrams of a tray for the aquaculture system of figures 1 or 2 according to different embodiments; Figure 8 shows a schematic cross-sectional view diagram of an example system of raceway tanks arranged in a stack for the aquaculture system of figures 1 or 2; Figure 9 shows schematic cross-sectional and plan view diagrams of an example tank for the aquaculture system of figures 1 or 2; and Figure 10 shows a schematic diagram of a method as described herein. 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 an aquaculture system 100 for culturing marine or aquatic organisms according to an embodiment of the present disclosure. The system 100 comprises a tank 102 including a culturing section 106 configured to hold a volume of liquid for culturing marine or aquatic organisms therein. Suitable species or organisms include any water dwelling organisms including but not limited to any species of echinoderms such as sea urchins, molluscs, crustaceans, 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. The tank 102 comprises an inlet 118 to supply an inlet flow of liquid into the culturing section 106, and an outlet 122 to receive an outlet flow and maintain a predefined liquid level in the culturing section 106 for culturing the marine or aquatic organisms. The tank 102 further comprises a drain 114 for removing liquid from the culturing section 106, and at least one spray nozzle 110 arranged to direct a jet of liquid along or towards at least a portion of a surface of the culturing section 106 for cleaning the surface. The at least one spray nozzle 110 is preferably integrated with the tank 102. The drain 114 is preferably an opening located in a base of the culturing section 106 such that substantially all of the liquid in the culturing section 106 can be drained or emptied through the drain 114 at least through gravity. The culturing section 106 refers, generally, to a region of the tank 102 in which aquatic organisms are cultured, housed or otherwise retained, and in which the liquid / water quality is controlled. This is to be contrasted with any other sections of the tank 102 which may hold liquid but not for culturing aquatic organisms in, for example a weir assembly of a racewaystyle tank (see figures 3(a) and 3(b)) which may be provided to receive the outlet flow from the culturing section 106, as described in more detail below. The system 100 further comprises a plurality of valves 112, 116, 120 to control the flow of liquid into and out of the tank 102. Specifically, the inlet 118 is operable by an inlet valve 120, the drain 114 is operable by a drain valve 116, and the at least one spray nozzle 110 is operable by a nozzle valve 112. In preferred embodiments, the valves 112, 116, 120 are electrically controllable and system 100 further comprises a controller 126 configured to control the valves 112, 116, 120 and thereby control and automate the operation of the system 100, as will be described in more detail below. For example, the controller 126 can be in wired or wireless communication with the valves 112, 116, 120 and the valves 112, 116, 120 configured to actuate or operate in response to a control signal received from the controller 126. The valves 112, 116, 120 can be solenoid type valves, or any other suitable valve that can be electrically actuated. Although figure 1 shows the valves 112, 116, 120 as external to the tank 102 it will be appreciated that any or all of the valves 112, 116, 120 may be located on or integrated with the tank 102. In preferred embodiments, the tank 102 is configured as a raceway tank, as described in more detail below with reference to figures 3 to 6. However, the disclosure is not limited to raceway tanks, and is applicable generally to any tank 102 suitable for culturing marine or aquatic organisms and which requires regular cleaning. A raceway tank is a substantially elongate longitudinal channel-shaped or rectangular-shaped tank or basin (i.e. having a length greater than its width) which is configured as a flow-through system, as is known in the art. Specifically, in a raceway tank 102 the inlet 118 is provided at one end (an inlet end) of the channel-shaped culturing section 106 and the outlet 122 is provided at the opposite end (the outlet end). During normal operation of the system 100, the drain valve 116 and the at least one nozzle valve 112 are closed, and the inlet valve 120 is open to supply a continuous inlet flow of liquid to the culturing section 106 of the tank 102 at the inlet 118 and cause an outlet flow of liquid at the outlet 122 through liquid displacement. This maintains a predefined liquid level in the culturing section 106 and produces a continuous flow of liquid through the culturing section 106 for maintaining a level of water quality, as is known in the art. The rate of liquid replacement in the tank is consistent and set to the normal culture biomass needs of the aquatic organisms being cultured. Over time, waste matter produced by the aquatic organisms being cultured and / or uneaten feed deposits and builds up on the base and bottom surface of the culturing section 106 which in turn causes a reduction in water quality. Regular cleaning of the tank 102 inner surfaces, particularly the base surface, is therefore required in order to maintain a required water quality. Traditionally, cleaning aquaculture tanks is a difficult and time-consuming task, not least because accessing the bottom of the tank is often hindered by the organisms being cultured resulting in high degrees of deposits of waste material (e.g., faeces and uneaten food). In addition, conventional raceway-style tanks while commonplace are limited by their very design. In particular, the longitudinal flow-through nature of raceway tanks can create a situation whereby the biomass that a raceway tank can hold can be limited by the length of the raceway itself due to reducing water quality along its length. For example, organisms at the inlet end of the raceway have access to cleaner, more oxygenated and less fouled water than those at the outlet end. In this way, conventional raceway tanks are often limited in the length and the biomass that they can hold at any one time. The aquaculture system 100 of the present disclosure represents a significant advancement in the art by providing an improved means for cleaning the tank 102 and maintaining high water quality, which in turn improves yield and survival rate of the cultured organisms. Specifically, in additional to the normal operation mode described above, the system 100 is further configured to operate in a cleaning mode whereby the liquid is removed or drained from the culturing section 106 through the drain 114, and the integrated spray nozzle(s) 110 are used to direct a high velocity jet or sheet of liquid along the base of the culturing section 106 to dislodge waste material and effectively clean the base surface. Specifically, fluid pressure and flow rate of the nozzles 110 is substantially greater than that of the inlet 118. Waste material entrained in the sheet of liquid is also removed through the drain 114, and once the tank 102 is cleaned (i.e. the spray nozzles 110 operated) for a predefined period of time, the tank 102 can then be re-filled and the system 100 returned to normal operation. As such, in the cleaning mode, the inlet valve 120 is closed, and the drain valve 116 and the at least one nozzle valve 112 are open. The general cleaning process, referred to herein as a cleaning cycle, involves (starting from the normal operation mode): closing the inlet valve 120 to stop the inlet flow and opening the drain valve 116 to empty liquid from the culturing section 106 of the tank 102; opening the at least one nozzle valve 112 to cause the spray nozzle(s) 110 to direct a jet of liquid at the exposed inner base surface of the tank 102 to clean it; and closing the drain valve 116 and opening the inlet valve 120 to fill the culturing section 106 with liquid to return the system 100 to normal operation. In specific examples, the entire cleaning cycle can be completed within 5 to 10 mins with appropriate valve timings, and the system 100 can be configured to rapidly empty / drain and fill the culturing section 106 to minimise the time the organisms are exposed to air, as will be described in more detail below. In this way, the cleaning cycle can be performed regularly and preferably multiple times a day to remove substantially all the liquid in the culturing section 106 along with any contaminants to improve the average water quality and hygiene of the tank 102. The system 100 can thus be used for efficient and effective culturing of organisms that are sensitive to water quality. The only caveat being that the organisms being cultured must be able to withstand regular short exposure to air. In preferred embodiments, the operation of the system 100 including the cleaning process is fully automated through the use of the controller 126 to substantially reduce the time, labour and costs of cleaning the tank 102 and improve the operational efficiency of the system 100 compared to traditional manually controlled cleaning processes and systems. The controller 126 can be configured to operate the system 100 24 hours a day and execute the cleaning cycle periodically, or according to a predefined schedule, preferably multiple times a day as required without immediate human intervention. In this way, the system 100 can both eliminate the need for human intervention in the cleaning process, and perform cleaning cycles more frequently than conventional manual cleaning approaches. However, it will be appreciated that the system 100 can also be manually operated, for example by a user manually operating the valves 112, 116, 120 as required, to perform a cleaning cycle which may still be substantially faster and less labour intensive than traditional manual cleaning processes, and thus the beneficial effects of the disclosure can be realised even without automation via the controller 126. The overall effect of the system 100 is that the average water quality and hygiene of the tank 102 can be maintained at a higher level over time in general operation, which is advantageous for the culture of species that can withstand regular short exposure to air (improving the yield and survival rate). Further, in preferred embodiments the liquid removed from the culturing section 106 during the normal mode and the cleaning cycle can be filtered and cleaned through a filtration system and returned to the culturing section of the tank 102 to make efficient use of water and resources and further improve operational efficiency, as described in more detail below. Figure 2 shows a schematic diagram of an aquaculture system 100 according to an example embodiment which is configured for rapid emptying of the culturing section 106 and for recycling the liquid flushed from the tank 102. The system 100 comprises a tank 102, at least one spray nozzle 110, at least one nozzle valve 112, a drain 114, a drain valve 116, an inlet 118, an inlet valve 120, an outlet 122, and a controller 126, as described above with reference to figure 1. However, in this example the system 100 further comprises a pumping arrangement 124, a filtration system 134, and a reservoir 132. The filtration system 134, reservoir 132, and tank 102 provide a liquid recirculation / recycle loop. In other examples, the system 100 may be provided with the recirculation loop but not the pumping arrangement 124, or vice versa. The reservoir 132 is in fluid communication with inlet 118 and the spray nozzle(s) 110 for supplying an inlet flow of liquid to the inlet 118 and a flow of liquid to the spray nozzle(s) 110. The inlet valve 120 and nozzle valve(s) 112 are arranged in line between the reservoir 132 and the respective inlet 118 and the spray nozzle(s) to control the liquid flows thereto. In alternative embodiments the reservoir 132 only provides a flow of liquid to the inlet 118. This may, for example, be preferable where an alternative liquid source is used for cleaning the culturing section 106 with the spray nozzle(s) 110, e.g. a mains fresh water source, rather than sea water or water for culturing the organisms. The filtration system 134 is in communication with the drain 114 and the reservoir 132 and is configured to receive and filter at least a portion of liquid removed from the culturing section 106 through the drain 114 and return filtered liquid to the reservoir 132 for re-use in operation. The filtration system 134 is operable to filter, clean, sanitise and / or purify liquid provided to it. It will be appreciated that the specific configuration of the filtration system 134 may vary based on the different types and amounts of waste product the filtration system 134 needs to handle. The pumping arrangement 124 is in fluid communication with the drain 114 and is operable to pump or drawn liquid out of the tank 102 through the drain 114 when the system 100 is in the cleaning mode. The pumping arrangement 124 is activated in the cleaning mode and deactivated in the normal mode. Preferably, the controller 126 is further configured to communicate with and control the pumping arrangement 124 to automate the operation of the system 100 and cleaning cycles. The pumping arrangement 124 advantageously may increase the speed at which liquid is drained from the tank to speed up the cleaning cycle and reduce the time aquatic organisms are exposed to air during the cleaning cycle. In preferred implementations, the pumping arrangement 124 comprises a mechanical pump. However, in alternative configurations a syphon pump can be used. In the illustrated embodiment, the pumping arrangement 124 is external to the tank 102, however, it will be appreciated that the pumping arrangement 124 may alternatively be situated within or integrated with the tank 102 and / or may be combined with the drain valve 116 as one integrated component. In a preferred implementation, the pumping arrangement 124 is arranged to pump or draw liquid out of the tank 102 through the drain 114 provided in the base of the tank 102. However, this is not essential. In an alternative example, the pumping arrangement 124 may instead be arranged to pump or draw liquid directly out of the culturing section of the tank 102 in addition to or instead of liquid being removed through the drain 114 via gravity. In this case, instead of the drain 114 being an opening in the base of the culturing section 106, the drain 114 may additionally or instead be part of the pumping arrangement 124 (e.g. the drain 114 may comprise a hose or pipe that extends from the pumping arrangement 124 to the base of the culturing section 106 for pumping the liquid from the tank 102). Preferably, the system 100 further comprises a sump tank 136 in fluid communication with the drain 114, the outlet 122, and the filtration system 134 for receiving and collecting the liquid from the drain 114 and outlet 122 prior to filtering. A sump tank is a term of the art and refers to a subsidiary tank in the aquaculture system in which no aquatic organisms are cultured or housed. The sump tank 136 may comprise a single tank, or separate sump tanks 136a, 136b for receiving liquid from the drain 114 (drain sump tank 136a) and the outlet 122 (outlet sump tank 136b) respectively, as illustrated in figure 2. In figure 2 the drain 114 is in fluid communication with the sump tank 136 via the pumping arrangement 124, however, the drain 114 may instead be in direct fluid communication with the sump tank 136 in examples wherein the pumping arrangement 124 is omitted. Figures 3(a) and 3(b) show schematic side and plan views of a specific embodiment of a tank 102 for the system 100, configured as a raceway-style tank 102. As described above, the tank 102 comprises a culturing section 106 with a base 108 and sidewalls 109 for holding a volume of liquid in which aquatic or marine organisms 104 can be cultured, at least one spray nozzle 110, a drain 114, an inlet 118 and an outlet 122. The raceway tank 102 is a substantially elongate longitudinal channel or rectangular-shaped tank having a length L substantially greater than its width W, as shown. The inlet 118 is located at an inlet end of the raceway tank 102 and the outlet 122 is located at the opposite outlet end of the raceway tank 102. In this example, the outlet 122 comprises a weir assembly 122, as is commonplace in raceway tanks. Aquatic organisms 104 to be cultured are located / supported in one or more trays 128 that are removably mountable in or to the culturing section 106 of the tank 102. Each tray 128 has a base 128b and sides 128s with perforations or holes and is configured, when mounted, to be at least partially submerged beneath the liquid level H in the culturing section 106 under normal operation such that aquatic organisms 104 in the tray 128 are also submerged. Each tray 128 is further configured such that, when mounted, the base 128b of the tray 128 is spaced apart from the base 128 of the culturing section 106 (described in more detail below with reference to figures 7(a) to 7(c)). In this way, each tray 128 supports or holds the organisms 104 in a region elevated above the base 108 of the culturing section 106, allowing the base 108 of the culturing section 106 to be cleaned using the nozzle(s) 110 without needing to remove the tray(s) 128 thus further reducing the level of human intervention needed to operate the system 100 to perform the cleaning cycles. Although only one tray 128 is shown, it will be appreciated that in practice the tank 102 may fit multiple trays 128. Figure 3(a) illustrates the tank 102 filled with liquid to a liquid level H and operating in the normal mode, where the drain valve 116 and nozzle valve(s) 112 are closed and the inlet valve 120 is open (the valves 112, 116, 120 are omitted for clarity but see, e.g., figure 1). During normal operation, an inlet flow F1 of liquid is continuously supplied through the inlet 118 at the inlet end to thereby cause an outlet flow F2 of liquid into the weir assembly 122 at the outlet end by displacement. There is no liquid flow from the spray nozzle(s) 110 and also no flow of liquid out of the culturing section 106 through the drain 114. Waste material which may deposit and build up on the base 108 over time under normal operation is illustrated by the dotted region M. The weir assembly 122 comprises a barrier or dam 122b over the top of which flows the outlet flow F2 of liquid to thereby maintain the predefined liquid level H (equal to the height of the barrier 122b) in the culturing section 106, as is known in the art. The weir assembly 122 further comprises an outlet 122o on a downstream side of the barrier 122b by which liquid in the outlet flow F2 can be removed from the tank 102. Preferably, the weir assembly 122 extends across the width W of the tank 102 such that the barrier 122b forms a containing sidewall of the culturing section 108 as shown in figures 3(b). With reference to figure 2, where the system 100 comprises a recirculation loop, the outlet 122o is preferably in fluid communication with the filtration system 134 (optionally via the sump tank 136). In the example shown, the outlet 122o is located in the bottom of the weir assembly 122 for draining liquid from the weir assembly 122 by gravity. In other examples, the weir assembly 122 itself may form a transverse channel configured to direct or flow liquid away and / or out of the tank 102 in a transverse direction, in which case the outlet 122o may be provided by the channel itself or a transverse side of the weir assembly 122 (not shown). However, it will be appreciated that the system 100 is not limited to weir-type assemblies, and the outlet 122 may in general comprise any type of apparatus in fluid communication with the tank 102 which is suitable for receiving an outlet flow F2 and maintaining predefined liquid level H in the culturing section 106. Figure 4 shows the raceway tank 102 in the cleaning mode, where the drain valve 116 and nozzle valve(s) 112 are open and the inlet valve 120 is closed (again the valves 112, 116, 120 are omitted for clarity but see, e.g., figure 1). In the cleaning mode, liquid is removed or drained from the culturing section 106 through the drain 114, as indicated by drain flow F3, such that the tank 102 is substantially empty as shown (there is no inlet flow F1 or outlet flow F2). The integrated spray nozzle(s) 110 are then used to direct a high velocity jet or sheet of liquid, indicated by nozzle flow F4, along the base 108 of the culturing section 106 to dislodge waste material and effectively clean the base surface 108. The nozzle flow F4 rate and pressure is substantially greater than the inlet flow F1 rate and pressure as indicated schematically by the relative size of the arrow. Waste material M dislodged by the high velocity jet or sheet of liquid becomes entrained in the nozzle flow F4, which is removed through the drain 114, as indicated. During this time, the tray 128 is suspended above the base 108 and nozzle flow F4, such that the aquatic organisms 104 are no longer submerged and are exposed to air. After a predetermined amount of time has elapsed sufficient to clean the tank 102, the system 100 returns to the normal mode by operating the valves 112, 116, 120 to rapidly fill the tank 102 to the predefined level H (see figure 3(a)), as will be described in more detail with reference to figure 5. In the illustrated example raceway tank 102, the base 108 of the culturing section 106 of the tank 102 is substantially flat over the majority of the length L of the culturing section 108 and includes a well or depression 130 at the outlet end adjacent the weir assembly 122 in which the drain 114 is located. The well 130 provides a portion of increased depth which serves, in conjunction with the high velocity nozzle flow F4 produced in the cleaning mode, to trap / collect waste material M entrained in the nozzle flow F4 and help funnel / guide liquid in the nozzle flow F4 into the drain 114. The placement and profile of the well 130 can also help to trap liquid in the vicinity of the drain 114 and thus prevent backflow of liquid (potentially including waste material M) towards the inlet end (that may result from the high velocity nozzle flow F4 reaching / impacting the barrier 122b of the weir assembly 122) which would otherwise take more time to flush into the drain 114. In this way, the well 130 can improve the overall cleaning and drainage of liquid in the cleaning mode. For this purpose, the well 130 preferably has a substantially rectangular cross-section as shown with a side portion 130s and base portion 130b that together provide a step down and / or abrupt change in depth of the culturing section 108. In particular, the side portion 130s is substantially perpendicular to the nozzle flow F4 to assist in trapping liquid and preventing backflow. However, it will be appreciated that a rectangular profile is not essential and the well 130 can take any shape suitable for trapping liquid (for example, the side portion 130s and / or base portion 130b may be substantially sloped or curved). ln preferred implementations, the tank 102 comprises a plurality of spray nozzles 110 located at the inlet end and distributed across the width W of the culturing section 106 as illustrated in the plan view of figure 3(b). This arrangement may assist in providing a substantially uniform high velocity sheet / laminar flow F4 of liquid across the width of the culturing section 106 for providing substantially uniform cleaning of the base 108. Although three substantially equally spaced nozzles 110 are shown in figure 3(b), it will be appreciated that the precise number and distribution of spray nozzles 110 is not critical provided that the combined jets of liquid produced from each nozzle 110 combine to provide for substantially uniform cleaning of the base 108. Optionally, the tank 110 may further comprise a plurality of spray nozzles 110 distributed along at least a portion of the length L of the base 108 of the culturing section 106 as shown in figure 3(b). For example, this may be useful in longer raceways for maintaining a high velocity of the nozzle flow F4 along the length L of the culturing section 106. The number and distribution of such longitudinally spaced spray nozzles 110 may vary dependent on the specific tank 102 design. Preferably, all the spray nozzles 110 are arranged to direct a jet of liquid towards the outlet end and the drain 114. However, it will be appreciated the direction of each spay nozzle 110 need not be identical and various spray patterns can be implemented to achieve the desired cleaning function, for example, in some implementations one or more of the spray nozzles 110 may be arranged to direct a jet of liquid onto the base 108 in a substantially transverse direction (not shown). In the above description of figures 3 and 4, the various liquid flows into and out of the tank 102 in the normal mode and cleaning mode are controlled by the respective valves 112, 116, 120, as described and depicted with reference to figures 1 and 2. A cleaning cycle, which involves switching the operation of the system 100 from the normal mode to the cleaning mode and back to the normal mode, can be implemented with appropriate valve timings and sequences, as describe below. Figure 5 shows a schematic diagram of example valve timings (left axis) for operating a cleaning cycle together with the corresponding liquid level LL (right axis) in the culturing section 106 versus time. Valve positions are indicated by solid lines and vary between 0 (closed) and 1 (open), and the liquid level LL is indicated by the dashed line and varies between empty (0) and filled (H). In this example, the system 100 starts in the normal mode whereby the inlet valve 120 is open (1) and the nozzle valve(s) 112 and drain valve 116 are closed (0), such that the liquid level LL in the culturing section 106 is maintained at the predefined liquid level H. At time A the system 100 is switched into cleaning mode, at which point the inlet valve 120 is closed (0) and the drain valve 116 is opened (0) to drain and empty liquid from culturing section 106, as indicated by the reduction in liquid level LL. In embodiments including a pumping arrangement 124, this can also be activated at time A to increase the rate at which liquid is emptied from the culturing section 106 (not shown). After a predefined period of time T1 has elapsed, equal to the time required to sufficiently drain and empty the culturing section 106, the nozzle valve(s) 112 is(are) opened (1) to activate the spray nozzle(s) 110 and clean waste material M from the exposed base 108 of the culturing section 108. After another predefined period of time T2 has elapsed, equal to the time required to sufficiently clean the base 108 of the culturing section 106, the drain valve 116 is closed (0) and the inlet valve 120 is opened (1) to beginning filling the culturing section 108 with liquid, as indicated by the rise in liquid level LL. Preferably, the spray nozzle(s) 110 remain activate for a period of time T3 after closing the drain valve 116 as shown, to increase the rate at which the culturing section 106 is filled with liquid. More preferably, the period of time T3 is calibrated and equal to the time required to fill the culturing section 106 as shown. After the period of time T3 has elapsed the nozzle valve(s) 112 is(are) closed and the system 100 is returned / restored to normal operation. In other examples, the spray nozzles 110 can be deactivated at a short period of time before, or substantially the same time as, closing the drain valve 116 (not shown). As described above, in preferred implementations the use of the pumping arrangement 124 to assist in the emptying of liquid from the culturing section 106 combined with the use of the nozzle flow F4 to assist in filling the culturing section 106 can provide for rapid draining and rapid filling to thereby minimise the total time T1+T2+T3 the aquatic organisms are exposed to air. Further, while the cleaning cycle can be implemented manually or semi-automatically by an operator actuating the valves 112, 116, 120 (i.e. physical actuation of a tap-type valve or electronic actuation of a solenoid-type valve), in preferred implementations the operation of the cleaning cycle is fully automated by the use of electronically controlled valves 112, 116, 120 and a controller 126 and can be run multiple times a day, periodically or according to a user-defined schedule, as required to maintain high average water quality levels in the culturing section 106. Figure 6 illustrates schematically the system 100 switching between the normal mode and cleaning mode (indicated by the hatched regions) multiple times over a much longer period of time compared to figure 5 (the status of the individual valves 112, 116, 120 is omitted for clarity). As shown, the system 100 is under normal operation for much longer periods of time than the cleaning cycles. Indeed, the system 100 advantageously reduces the total proportion of time required to clean the system 100. It will be appreciated that the length of the cleaning cycle will in practice vary depending on various factors including the dimensions of the tank 102 and the species of the aquatic organism 104 being cultured, and so may form a larger or small fraction of the total time than what is depicted. In a specific example implementation, a raceway tank 102 configured as shown in figures 3 and 4 has a 1 meter wide and 6 meter long culturing section 108 with three spray nozzles 110 distributed across the width of the culturing section 106 at the inlet end (similar to that shown in figure 3(b). In this specific embodiment, the culturing section 106 has a volume of approximately 3000 litres. Liquid is supplied to the inlet 118 (as inlet flow F1) and flows out the outlet (as outlet flow F2) at a rate of approximately 6000 litres per hour, such that the water in the culturing section 106 of the tank 102 is completely replaced twice per hour while maintaining a constant liquid level H. Liquid is supplied to each spray nozzle at a rate of approximately 15,000 litres per hour, and is subject to a pressure of approximately 10-20 psi (0.6-1.4 bar). Liquid is supplied to each spray nozzle 110 in a common supply line formed of a 50 mm diameter fluid conduit, and each spray nozzle 110 comprises a % inch (approximately 19 mm) aperture which together form a high velocity of sheet of liquid for cleaning the base 108. In this example, the cleaning cycle can be completed in under 5 minutes, and is repeated several times a day under control of the controller 128. The flow rate F4, aperture size and pressure at each spray nozzle 110 may depend on the specific implementation of the system 100. The volume and flow rates of liquid may vary depend on the specific implementation of the raceway tank 102, but preferably for raceway tanks, inlet flow F1 should equal at least the volume of the raceway tank per hour such that the water in the tank is replaced at least one per hour. The pressure at each spray nozzle 110 may vary and this may advantageously allow the spray nozzles 110 to be configured to optimally form the high velocity sheet of liquid. In general, for raceway tanks liquid is sprayed from each of the spray nozzles 110 at a flow rate which is 5-8 times greater than the inlet flow F1 rate. Figure 7(a) to 7(c) show schematic cross-sectional diagrams of three example configurations of a tray 128 suitable for the system 100 which can be removably mounted within the culturing section 106 of the tank 102 in a position such that the tray base 128b is spaced apart from the base 108 of the culturing section 106. In all examples, tank 102 has a pair of opposing sidewalls 109 and a base 108 forming the culturing section 106, and the tray 128 is removably mounted between them. The tank 102 may be a raceway tank 102 as described above, or a different tank configuration. In figure 7(a), the tray sidewall(s) 128s comprise(s) one or more lips or rims 1281 configured to rest on the sidewalls 109 of the culturing section 106 of the tank 102 to thereby support the tray 128 in a position elevated from the base 108 as shown. The dimensions of the sidewalls 128s and / or the position of the lips or rims 1281 can be configured such that the aquatic organisms 104 are submerged beneath the predefined liquid level H as shown. In figure 7(b), the opposing sidewalls 109 of the culturing section 106 comprise a protrusion or ledge 1091 and the tray sidewall(s) 128s comprise(s) one or more lips or rims 1281 configured to rest on and / or engage the protrusion or ledge 1091 of the sidewalls 109 of the culturing section 106 to thereby support the tray 128 in a position elevated from the base 108 as shown. The dimensions of the sidewalls 128s, the position of the lips or rims 1281 and / or the position of the protrusion or ledge 1091 can be configured such that the aquatic organisms 104 are submerged beneath the predefined liquid level H as shown. In the case of a raceway tank 103, the configurations of figures 7(a) and 7(b) may allow the tray 128 to slide along the raceway tank 102, e.g. in order to easily vary in the position of the tray 128 with respect the inlet end and the outlet end. In figure 7(c) the tray 128 comprises legs 1281 to support the -U - tray 128 on the base 108 of the culturing section 106 in a position elevated from the base 108 as shown. The length of the legs 1281 can be configured such that the aquatic organisms 104 are submerged beneath the predefined liquid level H as shown. This may be advantageous in wider tanks 102 where there is a significant distance between the sidewalls 109. Where the tank 102 comprises multiple trays 128, their removable and optionally slidable nature may allow for multiple groups of aquatic organisms being cultured simultaneously to be placed into and removed from the tank 102 separately and hence facilitates simultaneous culturing of organisms which have disparate life cycles. Figure 8 shows a schematic view of an embodiment of system 100 comprising multiple tanks 102, 102’, 102” stacked on top of each other. Specifically, figure 8 shows three iterations of the tank 102 described above with reference to figures 3 and 4. However, it will be appreciated that more or less tanks 102 can be arranged in a stack as required by the specific situation. In this case, each tank 102 has an individual inlet 118, outlet 122, spray nozzles 110 and drain 114 and each tank 102 is preferably independently controllable via its respective valves 112, 116, 120 (reference numerals marked as ‘ and "indicate labelling for the second and third iteration of the tank 102’ and 102” respectively). Further, with reference to figure 2, all of the tanks 102, or a subgroup of tanks 102 can be serviced by / share the same reservoir 132, filtration system 134, and sump tank 136, and this case, any / all of the inlets 118, outlets 122, nozzles 110, and drains 114 can be connected in parallel, which may advantageously improve the efficiency of delivering fluid and removing fluid from any / all of said tanks 102. In this case the volumetric size of the reservoir 132, filtration system 134 and sump tank 136 may be correlated to the number of tanks 102 sharing the same reservoir 132. The same controller 126 can be used to control all the tanks 102, or multiple different controllers 126 can be used. In a further alternative embodiment of system 100, the multiple tanks 102 in figure 8 may be arranged in series such that the outlet flow F2 of a first tank may provide the inlet flow F1 of a second tank in the series. In this embodiment the tanks 102 may be arranged ‘end to end’. Figure 9 shows schematic cross-sectional side and plan views of an example tank 102 for the system 100 according to alternative embodiment in which the tank 102 is configured as a rotational flow-style tank 102. A rotational flow tank is an aquaculture tank in which liquid flows in a circular motion about a centre of the tank 102. In this example, the rotational flow tank 102 comprises a plurality of inlets 118 arranged around the perimeter of the tank 102, and a drain 114 arranged in the centre of the tank 102. A plurality of nozzles 110 are also arranged around a perimeter of the tank 102 as shown. Similar to figures 3 and 4, the drain 114 is preferably situated in a circular well 130 to trap liquid and waste matter M during the cleaning cycle. A plurality of trays 128 can be arranged in a substantially circular path around the centre of the rotational flow tank, as shown (in this example, the trays 128 preferably have legs 1281 as shown in figure 7(c)). Figure 10 shows a schematic flow diagram of a method 500 of operating the system 100 according to an embodiment of the disclosure. In step 510, the method 500 comprises closing an inlet valve 120 to stop an inlet flow F1 of liquid into the culturing section 106. In step 520, the method 500 comprises opening the drain valve 116 to empty liquid from the culturing section 106 of the tank 102 through the drain 114, and preferably further comprises activating a pumping arrangement 124 to actively pump liquid out the culturing section 106. In some examples, step 510 may happen simultaneously to step 520. In step 530, the method 500 comprises operating the at least one nozzle valve 112 to cause a jet of liquid to be directed along at least a portion of the base 108 of the culturing section 106 by the at least one spray nozzle 110 for a predefined period of time T2 (optional T2+T3) to clean the surface of the base 108 and flush dislodged waste matter M through the drain 114. In step 540, the method 500 comprises filling the culturing section 108 with liquid to the predefined liquid level H by closing the drain valve 116. This preferably includes opening the inlet valve 120 to supply an inlet flow of liquid to the culturing section 106 and further preferably includes closing the nozzle valve(s) 112 after a predefined period of time T3 has elapsed after closing the drain valve 114. It will be appreciated that the exact order and duration of each step will depend on the specifications of the tank 102 in use, and that the method may be adapted to optimally match the time required to drain and or fill said tank 102 to minimise the time the system is being cleaned and thus ensure maximum efficiency of the system. In a further alternative embodiment, wherein the tank 102 is a raceway tank in a series of tanks such that the inlet flow F1 is itself an outlet flow F2 from a weir assembly of a previous tank in the series, step 510 may not occur as the inlet flow may not be governed by a valve. In such an embodiment the drain is preferably sufficiently sized such that the drain flow of liquid F3 is substantially larger than the inlet flow F1 to thereby still substantially drain the tank 102 of all liquid. It will be understood that the present disclosure has been described above purely by way of example, and modifications of detail can be made within the scope of the disclosure. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure 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 disclosure. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims. 25 03 25

Claims

1. An aquaculture system for culturing aquatic organisms, comprising:a tank having a culturing section with a base, the tank including at least one5 integrated spray nozzle arranged in fixed relation at or near the base to direct a jet of liquid along at least a portion of the base for cleaning the at least a portion of the base;a drain provided at or near the base of the culturing section for removing liquid from the culturing section; andone or more valves including at least one nozzle valve operable to control a flow of10 liquid to said at least one spray nozzle; andwherein the system is configured to operate in a cleaning mode, whereby liquid is removed from the culturing section through the drain such that the culturing section is substantially empty, and the at least one nozzle valve is opened for a predefined period of time to provide a flow of liquid to the at least one integrated spray nozzle for cleaning the at 15 least a portion of the base surface of the culturing section.

2. The system of Claim 1, wherein the tank is a raceway tank and further comprises: an inlet at or near a first end of the culturing section operable to supply an inlet flow of liquid into the culturing section; and20 a weir assembly at or near a second end of the culturing section to receive an outlet flow and maintain a predefined liquid level in the culturing section, andwherein the system is configured to operate in a normal mode whereby an inlet flow of liquid is supplied through the inlet to thereby cause an outlet flow of liquid into the weir assembly by displacement.

253. The system of Claim 2, wherein the one or more valves further include an inlet valve to control the inlet flow of liquid through the inlet, wherein the inlet valve is open in the normal mode and closed in the cleaning mode.30 4. The system of any preceding claim, wherein the one or more valves further include a drain valve to control the removal of liquid from the culturing section through the drain, wherein the drain valve is open in the cleaning mode; and optionally or preferably when25 03 25dependent directly or indirectly from claim 2, wherein the drain valve is closed in the normal mode.

5. The system of any preceding claim, further comprising a pumping arrangement in5 communication with the drain and operable to pump liquid out of the tank through the drain in the cleaning mode; and optionally or preferably, wherein the pumping arrangement comprises a mechanical pump or a syphon pump.

6. The system of any preceding claim, further comprising a controller configured to10 control the one or more valves to thereby control an operating mode of the system.

7. The system of claim 6 when dependent on claim 5, wherein the controller is further configured to control the pumping arrangement.15 8. The system of Claim 7 when dependent directly or indirectly from claim 2, wherein the controller is configured to operate a cleaning cycle in which the system is switched from the normal mode to the cleaning mode for a predefined period of time; and optionally or preferably, wherein the cleaning cycle is operated periodically or according to a predefined schedule.

209. The system of any proceeding claim, further comprising a plurality of spray nozzles distributed along a transverse and / or longitudinal direction of the culturing section.

10. The system of Claim 9, wherein at least some of the plurality of spray nozzles are25 distributed along a transverse direction at or near an inlet end of the culturing section; and / or wherein at least some of the plurality of spray nozzles are distributed along substantially an entire length of the culturing section.

11. The system of any preceding claim, further comprising a tray removably mountable to 30 the tank, wherein the tray configured to support or retain aquatic organisms within the culturing section in a region spaced apart from the base of the culturing section.25 03 2512. The system of Claim 11, wherein the tank comprises longitudinal sidewalls and the tray is removably mountable to at least one of the longitudinal sidewalls.

13. The system of any preceding claim, wherein the base of the culturing section5 comprises a well or depression of increased depth, and wherein the drain is positioned at or in the drainage portion.

14. The system of any preceding claim, wherein at least one of the at least one spray nozzle is arranged to direct a jet of liquid towards the drain.1015. The system of Claim 2 or any claim dependent directly or indirectly from Claim 2, further comprising a reservoir for supplying an inlet flow of liquid to the inlet, and a filtration system in communication with the drain and the reservoir, wherein the filtration system is configured to filter at least a portion of liquid removed from the culturing section through the 15 drain and return filtered liquid to the reservoir.

16. A method for operating an aquaculture system comprising a tank having a culturing section with a base, the tank including at least one integrated spray nozzle arranged in fixed relation at or near the base to direct a jet of liquid along at least a portion of the base for 20 cleaning the at least a portion of the base, and one or more valves including at least onenozzle valve operable to control a flow of liquid to said at least one spray nozzle, the method comprising:operating a cleaning cycle, comprising:removing liquid from the culturing section of the tank such that the culturing25 section is substantially empty; andoperating the at least one nozzle valve to cause a jet of liquid to be directed along at least a portion of the base of the culturing section by the at least one spray nozzle for a predefined period of time; andfilling the culturing section with liquid to a predefined liquid level in the tank. 3017. The method of Claim 16, wherein the system comprises a drain provided at or near the base of the culturing section for removing liquid from the culturing section, and the one or25 03 25more valves include a drain valve to control the removal of liquid from the culturing section through the drain, and wherein:removing liquid from the culturing section comprises opening the drain valve to empty liquid from the culturing section through the drain; and5 filling the culturing section with liquid comprises closing the drain valve.

18. The method of Claim 17, wherein:removing liquid from the culturing section further comprises operating a pumping arrangement in communication with the drain to pump liquid out of the culturing section.1019. The method of any of Claims 16 to 18, further comprising operating the system in a normal mode comprising:supplying an inlet flow of liquid to a first end of the culturing section of the tank; and removing an outlet flow of liquid at a second end of the culturing section to maintain a 15 predefined liquid level in the culturing section, and optionally or preferably to produce acontinuous flow of liquid through the culturing section of the tank.

20. The method of Claim 19, wherein: the step of removing liquid from the culturing section further comprises stopping the inlet flow; and wherein the step of filling the culturing 20 section with liquid further comprises supplying the inlet flow of liquid to the culturing section.

21. The method of Claim 20, wherein the one or more valves include an inlet valve to control the inlet flow of liquid to the culturing section, and wherein:stopping the inlet flow comprises closing the inlet valve; and25 filling the culturing section with liquid to the predefined liquid level comprises opening the inlet valve.

22. The method of any of Claims 16 to 21, wherein the system further comprises a controller configured to control one or more valves to thereby control the operation of the 30 system, and wherein the method comprises:using the controller to operate the one or more valves; and preferably, when dependent directly or indirectly from claim 21, using the controller to operate the pumping arrangement.

23. The method of any of Claims 16 to 22, further comprising:filtering the liquid emptied or removed from the culturing section of the tank; storing the filtered liquid in a reservoir; and5 using the stored filtered liquid to fill the culturing section and / or, when dependent directly or indirectly from claim 19, to supply the inflow of liquid to the culturing section.25 03 25

Images