Submersible fish tank with a movable water discharge column

Abstract

The invention relates to a closed submersible fish tank (1) for rearing fish. The tank (1) has a flexible exterior enclosure (2) and a water discharge column (40) for transporting the tank water, suspended from a top portion of the tank (1). The water discharge column (40) is at least partly permeable and provides a housing for fish tank infrastructure while serving as a barrier preventing fish from reaching the fish tank infrastructure. The fish tank (1) includes water supply means and together with the permeable water discharge column (40) an advantageous water flow is provided. Also, the water discharge column (40) may be vertically repositioned providing adjust strain imposed on the flexible exterior enclosure (2).

Description

[0001] Submersible fish tank with a movable water discharge column

[0002] Field of the invention

[0003] The invention relates to closed and submersible fish farms with a water replacement system including a water discharge column within the tank.

[0004] Background

[0005] In recent years, the demand for salmon has increased significantly due to its numerous health benefits and versatile culinary qualities. This has led to a surge in the number of fish farms around the world, where salmon is produced in a controlled and predictable environment. One critical aspect of salmon farming is water quality, as the health and growth of the fish directly depend on the quality of water in the farm.

[0006] Closed and submerged fish farms are commonly used for salmon aquaculture, where the fish are grown in tanks or cages submerged in water. In these farms, water circulation and water replacement is vital to maintain the optimal environment for the fish. The water must be continuously circulated and replaced to provide sufficient oxygenation, remove waste materials, and maintain a stable temperature throughout the tanks.

[0007] In existing water circulation systems for fish farms, water is moved using pumps, propellers, or diffusers. However, these systems have several limitations, including high energy consumption, low efficiency, and limited control over the flow rate and direction.

[0008] Therefore, the present invention aims to address these issues by providing a new and improved water replacement system for closed and submerged fish farms.

[0009] Closed and submerged fish farms may include flexible enclosures such as polymer membrane and submerged fish farms may be prone to harsh weather conditions with tall waves and strong currents. The invention therefore also aims at providing means for adjusting and protecting a flexible enclosure for submerged fish farms.

[0010] To comply with regulatory mandates, fish farms may have a water outlet positioned at a low point within the fish tank to allow for easy drainage. However, preventing waste discharge from these outlets is key to avoid environmental contamination and filter strain. Thus, the present invention aims to prohibit fish from inhabiting the area above the water outlet, redirecting waste accumulation elsewhere and safeguarding against escape.

[0011] Overall, the invention has the potential to significantly improve water quality and fish health in closed and submerged fish farms, making fish farms resistant environmental loading, while reducing energy consumption and operational costs.

[0012] Summary of the invention

[0013] The invention relates to a submersible fish rearing tank having a flexible exterior enclosure forming a closed fish habitat, an upper utility transition element, water supply means adapted to pump water into the tank to provide a pressure inside the tank exceeding a pressure acting on the outside of the tank and a water outlet. The tank further includes a water discharge column configured to guide or transport fluid, the water discharge column in fluid connection with the inner volume of the tank and in fluid connection with the water outlet, wherein the water discharge column comprises a non-permeable portion in connection with the flexible exterior enclosure.

[0014] The water discharge column may be connected to the upper utility transition element by connection lines extending between the upper utility transition element and the water discharge column wherein the tank comprises adjusting means for hoisting and lowering the water discharge column within the tank.

[0015] The invention relates to a submersible fish rearing tank comprising: a flexible exterior enclosure forming a closed fish habitat, an upper utility transition element, water supply means adapted to pump water into the tank to provide a pressure inside the tank exceeding a pressure acting on the outside of the tank, a water outlet, a water discharge column configured to guide or transport fluid, the water discharge column in fluid connection with the inner volume of the tank and in fluid connection with the water outlet, wherein the water discharge column comprises a non-permeable portion in connection with the flexible exterior enclosure, and wherein the tank comprises adjusting means for hoisting and lowering the water discharge column within the tank.

[0016] The invention further relates to a said fish rearing tank within the water discharge column is connected to the upper utility transition element by connection lines extending between the upper utility transition element, and the water discharge column, wherein the connection lines is connected to connection line stopping means.

[0017] The invention further relates to said fish rearing tank, wherein the water discharge column comprises a permeable portion located above the non-permeable portion.

[0018] The invention further relates to said fish rearing tank, wherein the water supply means comprises at least one water supply column in fluid connection with the tank wherein at least one water supply column is attached to the exterior enclosure and comprises a pump unit.

[0019] The invention further relates to said fish rearing tank, wherein each water supply column comprises a plurality of water discharge means aligned in a vertical array along a surface of the water supply column, the water discharge means adapted to discharge water in the horizontal plane and / or at an angle relative to a tangential component of the exterior enclosure.

[0020] The invention further relates to said fish rearing tank, wherein the upper utility transition element comprises at least one connection line maintenance access through which maintenance personnel may gain access to the connection lines and the adjusting means. The invention further relates to said fish rearing tank, wherein the permeable portion comprises a mesh made of at least one of rope, yam, chain, fabric or plastic material.

[0021] The invention further relates to said fish rearing tank, wherein the water discharge column comprises:

[0022] - a top plate enclosing its top end portion discharge column; and

[0023] - at least one intermediate connection line located within the permeable portion connected to and extending between the non-permeable portion and the top plate;

[0024] - wherein the connection lines comprises a plurality of connection lines connected to and the extending between the top plate and the upper utility transition element.

[0025] The invention further relates to said fish rearing tank, wherein each intermediate connection line is connected close to the perimeter of the top plate at one end, and close to the perimeter of the non-permeable portion at the other end.

[0026] The invention further relates to said fish rearing tank, wherein the permeable portion has a conical shape tapered towards the non-permeable portion.

[0027] The invention further relates to said fish rearing tank, wherein infrastructure such as pipes, hoses and cables may extend within the water discharge column along a vertical axis.

[0028] The invention also relates to a method of lifting the said water discharge column said fish rearing tank, comprising the steps of

[0029] - pulling the adjusting means until the water discharge column moves upwards to a desired level;

[0030] - fixing the adjusting means to a connection point;

[0031] The invention relates to said method of lifting the water discharge column, further comprising the steps of:

[0032] - releasing the stopping means;

[0033] - tensioning the connection lines; - locking the stopping means.

[0034] The invention also relates to a method of lowering the said water discharge column said fish rearing tank, comprising the steps of

[0035] - lowering the adjusting means until the water discharge column reaches a desired level;

[0036] - fixing the adjusting means to a connection point.

[0037] The invention also relates to a method of lowering the said water discharge column said fish rearing tank, further comprising the steps of:

[0038] - tensioning the adjusting means;

[0039] - releasing the connection lines from the stopping means;

[0040] - locking the stopping means.

[0041] List of figures

[0042] Fig. 1 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention;

[0043] Fig. 2A is a cut-out perspective view of a top portion of a water discharge column according to the invention;

[0044] Fig. 2B is a cut-out perspective view of the water discharge column at a transition point between a permeable portion a the non-permeable portion;

[0045] Fig. 3 is a cross-sectional perspective view of the housing of the upper utility transition element according to the invention;

[0046] Fig. 4 is a cross-sectional side view of a submersible fish rearing tank of the present invention with an alternative water discharge column;

[0047] Fig. 5 is a cut-out perspective view of the non-permeable portion according to the embodiment of Fig. 5;

[0048] Fig. 6 is a cross-sectional side view of a submersible fish rearing tank of the present invention according to an alternative embodiment;

[0049] Fig. 7 is a cross-sectional side view of a submersible fish rearing tank of the present invention according to the embodiment of Fig. 6 including alternative lifting means; Fig. 8 is a cross-sectional side view of a submersible fish rearing tank of the present invention according to the embodiment of Fig. 1 or Fig. 4 including alternative lifting means;

[0050] Fig. 9 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention according to the embodiment of Fig. 6 with an integrated winch; and

[0051] Fig. 10 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention according to the embodiment of Fig. 1 or Fig. 4 with an integrated winch.

[0052] Detailed description

[0053] Fig. 1 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention. The submersible fish tank 1 includes an exterior enclosure 2. The exterior enclosure 2 may be flexible and provides a closed fish habitat for rearing live fish. The fish rearing tank 1 is adapted to be completely submerged during operation, i.e. during fish rearing. Seen from an elevation (not shown) the fish tank has a substantially circular cross-section.

[0054] The fish habitat and the tank 1 is sufficiently closed to allow a pressure to build up inside the tank 1. The internal hydrodynamic pressure forces the exterior enclosure 2 to maintain its shape as illustrated in Fig. 1 during operation.

[0055] The exterior enclosure 2 is preferably at least partly made of a flexible membrane comprising a material such as PE, PVC, latex, nylon, flexible plastic or fabric material. The exterior enclosure 2 may also have elastic properties. The exterior enclosure 2 may also at least partly be made of a rigid material.

[0056] Although the tank 1 is closed, the tank 100 may receive seawater (fresh or saline), fluids such as air and oxygen, feed, and furthermore discharge used water and waste. The term “closed” used in this application does therefore not exclude the presence of inlets and outlets, but is used to distinguish the invention from fish farms with highly permeable net cages, open-air basins etc. Water intake and discharge may be autonomously controlled by a controller (not shown) connected to a plurality of sensors and cameras installed in the tank 100, thereby allowing controlled water treatment and flow for achieving optimal fish rearing conditions and optimal power usage. The pressure inside the tank 100 prevents ingress of unwanted elements in the event of a leak.

[0057] Incoming and outgoing water may be filtered to prevent sea lice from entering the tank 1 , and from polluting the surrounding environment, although the tank 1 water may also avoid lice issues by replacing the internal water in such a rate that sea lice would not be able to latch on to the fish.

[0058] Fig. 1 further shows that the submersible fish rearing tank 1 includes a first water supply column 30 and a second water supply column 30’ attached to the exterior enclosure 2, preferably on diametrically opposite sides. Each water supply column 30, 30’ comprises an internal channel for transporting water. Each water supply column 30, 30’ can be a rigid or flexible tubular and elongated structure, preferably cylindrical but may have a rectangular or elliptical cross-section, extending vertically along the exterior enclosure 2 of the tank 1 in parallel with the vertical centre axis of the tank 1. The supply columns 30, 30’ may be slightly curved to accommodate the shape of the submersible fish rearing tank 1 and may be integrated into the exterior enclosure 2.

[0059] The water supply columns 30, 30’ each comprises means for transporting fluid through the water supply columns 30, 30’. The means for transporting fluid may be pump units 31 , 3T located at a lower and / or upper end of each water supply column 30, 30’, wherein an opposite end may be closed or capped.

[0060] Water may be discharged substantially in the horizontal plane from the supply columns 30, 30’ via an outlet in fluid communication with the inner volume of the fish tank 1 . Preferably the water supply columns 30, 30’ comprise a plurality of nozzles 122 or holes or perforations or openings in fluid communication with the inner volume of the fish tank 1 . The nozzles 122 may be crafted and positioned to discharge water in the horizontal plane, i.e. directed / extending along the horizontal plane. Thereby the water supply columns 30, 30’ are adapted to provide an initial horizontal flow pattern within the tank, providing an evenly distributed water flow along the vertical axis of the supply columns 30, 30’.

[0061] The nozzles 122 may be aligned in a vertical array along a surface of the water supply column 30, 30’. The nozzles 122 comprise outlets in fluid communication with the inside of the tank 1 . The nozzles 122 may be oriented at an angle with a tangential component to create rotational flow inside the tank 1. The nozzles 122 of each of the supply columns 30, 30’ may be oriented in the same direction to create the rotational flow inside the tank 1 . The nozzles 122 may also be aimed in different directions to create any desired flow inside the tank 1 .

[0062] The fish tank 1 is designed to provide an optimal water flow pattern for the fish. In aspects the water supply columns 30, 30’ are attached to the side walls of the tank 1 for supplying fresh water with a sufficiently strong current to the internal fish habitat. The water supply columns 30, 30’ are in fluid communication with a water source located outside the tank 1 .

[0063] The exterior enclosure 2 is fixed to the upper utility transition element 110 and to the lower utility transition element 111. The utility transition elements 110, 111 may be rigid and preferably made of metal, plastic or composite materials.

[0064] The upper utility transition element 110 may include a buoyancy element (not shown), such as a dynamic ballast tank, keeping the tank 1 afloat at a desirable depth. The upper utility transition element 110 may include a housing 28 having an inner volume. The fish tank 1 and / or the upper utility transition element 110 may be moored to a floating structure (not shown) topside for buoyancy and / or stability. However the fish tank 1 may also be held afloat only by means of integrated buoyancy means (not shown).

[0065] The lower utility transition element 111 may include a weight element, such as a heavy solid material. The upper utility transition element 110 provides buoyancy while the lower utility transition element 111 provides gravity, counteracting any tilting movement and ensures that the tank always returns to an upright position. The tank 1 may also be moored to the seabed. The tank 1 may also be moored to the seabed without the need for a lower utility transition element 111.

[0066] The utility transition elements 110, 111 may provide a transition for at least one of a water inlet, a water outlet, a gas outlet, an air inlet, and connections for instrumentation.

[0067] The lower utility transition element 111 may be shaped conical or frustoconical being tapered towards the bottom. This allows internal sludge, fish excrements, debris, dead fish and other waste to gather in the lower utility transition element 111 from which the waste may be extracted and disposed. Keeping fish away from the central part of the tank can have advantages, as it helps to avoid the introduction of fish waste, sediment, or debris into the central water flow. A conical shape will force the fish even further away from the central area of the tank 1 .

[0068] The tank may comprise a water outlet 80 located at a lower portion of the tank 1 . The lower utility transition element 111 may comprise a water outlet 80 located at a lower portion of the lower utility transition element 111.

[0069] The submersible fish tank 1 comprises a water discharge column 40 (also referred to as a centre column or central discharge column) located in the centre of the fish tank 1 , extending along a vertical axis of the fish tank 1 , preferably along the central vertical axis of the tank 1. The water discharge column 40 defines an inner volume and is at least partly hollow or annular, configured to guide or transport fluid. The water discharge column 40 may serve both as a conduit for fluids (mainly seawater) and as a housing for internal infrastructure 46 such as pipes, hoses and cables extending through the water discharge column 40, typically extending between the lower utility transition element 111 and the upper utility transition element 110. The infrastructure 46 may comprise a tube for transporting dead fish and waste accumulated in a lower part of the tank 1 through the water discharge column 40 and to further towards a topside depot. The water discharge column 40 may also serve as a barrier preventing fish from accessing the internal infrastructure 46 (see Fig. 2A and 2B) and from following the internal water flow within the water discharge column 40.

[0070] The water discharge column 40 is at least partly permeable. The water discharge column 40 may comprise a filter 82 for preventing unwanted particles or biomass from exiting the tank 1 .

[0071] The water discharge column 40 may comprise an upper permeable portion 45 and a lower non-permeable portion 44. The non-permeable portion 44 is preferably rigid for providing support. The non-permeable portion 44 can be made of metal, plastics and / or composites.

[0072] The water discharge column 40 and / or the non-permeable portion 44 may be fixed or otherwise connected directly to the lower utility transition element 111. The water discharge column 40 may be connected indirectly to the upper utility transition element 110 via connection lines 20 such as ropes, chains or wire (see Fig. 2A and 2B). The non-permeable portion 44 may be in direct or indirect connection with the flexible enclosure 2, so that when the water discharge column 40 is adjusted e.g. hoisted or lowered, the flexible enclosure 2 is also adjusted accordingly.

[0073] The water discharge column 40 may be fixed directly to a lower rigid portion of the tank 1 via the non-permeable portion 44. Preferably the lower end of the non- permeable portion 44 is fixed directly to the inner portion of the lower utility transition element 111. The non-permeable portion 44 is sealed to the lower utility transition element 111 so that waste accumulated in the lower part of the tank 1 and on top of the of the utility transition element 111 does not enter the exiting water flow within the non-permeable portion 44. Such waste is thereby isolated and prevented from exiting the tank 1 and will be extracted separately. The non-permeable portion 44 extends a distance above the lower utility transition element 111 and is in fluid connection with the water outlet 80. The non-permeable portion 44 is typically cylindrical. The non-permeable portion 44 may comprise a filter 82 for preventing unwanted particles or biomass from exiting the tank 1.

[0074] The water discharge column 40 is in fluid communication with the water outlet 80. Water may pass from the supply columns 30, 30’, into the internal tank 1 volume, through the permeable portion 45, downwards through the water discharge column 40 and exit through the water outlet 80. The water outlet 80 may comprise a waste filter (not shown).

[0075] The water discharge column 40 may comprise a top plate 42 (i.e. cap / lid / ceiling) enclosing its top end portion. The water discharge column 40 is suspended from the upper utility transition element 110 by means of at least one connection line 20 (also referred to as a tether) such as rope, cable, wire or chain connected to the top plate 42. The top plate 42 prevents fish from entering the water discharge column 40 and serves as a supporting platform.

[0076] The connection lines 20 thereby carry the weight of at least the water discharge column 40 and the lower utility transition element 111. In the event the buoyancy of the upper utility transition element 110 is more than the weight of the remaining part of the tank 1 , the connection lines 20 serve to restrain the top part of the tank 1 preventing the upper utility transition element 110 and lower utility transition element 110 from traveling away from each other.

[0077] The burden of supporting both the water discharge column 40 and the lower utility transition element 111 is borne by the connection lines 20. Should the upper utility transition element 110 generate more buoyancy than the remaining tank 1 , the connection lines 20 will additionally serve to tether the top portion of the tank 1 , thus preventing any displacement between the upper and lower utility transition elements 110. Although the exterior enclosure 2 might bear some of the weight of the water discharge column 40 and lower utility transition element 111 , it is important to avoid overburdening the exterior enclosure 2 as this could result in damage or deformation. However, applying a certain amount of tension to the exterior 2 is advantageous for providing a stable and hydrodynamic shape. Consequently, there is a need for a mechanism that can regulate the tension of the exterior enclosure 2, allowing it to stretch to the desired level without having to support excessive weight.

[0078] The connection lines 20 may be connected to the water discharge column 40 and to the upper utility transition element 110. In aspects at least one of the connection lines 20 is connected to the top plate 42, and to the utility transition element 110.

[0079] Fig. 2A is a cut-out perspective view of a top portion of the water discharge column 40 within the submersible fish tank 1. Fig. 2B is a cut-out perspective view of the water discharge column 40 within the submersible fish tank 1 at a transition point between the permeable portion 45 and the non-permeable portion 44.

[0080] Referring to Fig. 1 and 2A, the upper utility transition element 110 may comprise a connection line support portion 24 providing a support structure from which the connection lines 20 may extend into the fish tank 1. The connection line support portion 24 may be located at a top portion of the upper utility transition element 110. Preferably at least one of the connection lines 20 is connected to a connection point 440 connected to the top plate 42 and to the connection line support portion 24. The connection lines 20 may be connected to the upper utility transition element 110 via connection lines such as chain blocks, chain hoists, snap lock, snap hooks, block & tackle, shackles or hooks.

[0081] The connection lines 20 may run past line stopping means 21 suspended from the connection line support portion 24. The stopping means 21 functions as a conventional chain / line stopper. The stopping means 21 has at least two modes, a first mode where the stopping means 21 locks the connection line 20 and a second mode where the stopping means 21 releases the connection line 20 allowing it to run freely. The connection lines 20 typically runs through the stopping means 21 leaving an excess line 20’.

[0082] The upper utility transition element 110 may include at least one connection line maintenance access 23 e.g. a hatch, door, lid, hole or opening through which maintenance personnel may gain access to the connection line 20 and the stopping means 21. The excess line 20’ may pass through the connection line maintenance access 23 and be collected, stored and / or wound at a nearby location.

[0083] The water discharge column 40 may be lowered and hoisted inside the fish tank 1 along with the connection lines 20 by means of a lifting line 43 connected to a lifting line connection point 22 such as a chain block, chain / line stopper, chain hoist, snap lock, snap hook, block & tackle, shackle or hook. The lifting line 43 may also be called hoist line, suspension line, adjustment line, hoist cable etc. The lifting line 43 may be a wire, cable, chain or any other suitable material for supporting the weight of the water discharge column 40.

[0084] Referring to Fig. 2B, the lifting line 43 is connected to the water discharge column 40. The top plate 42 may comprise at least one opening for allowing through at least one piece of infrastructure 46 and a lifting line 43. Preferably the lifting line 43 extends through an opening in the top plate 42, continuing through the water discharge column 40 and finally reaching a connection point 441 connected to a lower portion of the water discharge column 40, preferably to the non-permeable portion 44.

[0085] The water discharge column 40 may be provided with a hoist support element 41 which is a structure or platform fixed to the water discharge column 40 - preferably it is fixed to the non-permeable portion 44. The connection point 441 is preferably connected to the hoist support element 41 . The lifting line 43 may be connected to the connection point 441 by means of a connection lines such as a chain block, chain hoist, snap lock, snap hook, block & tackle, shackle, or hook. The lifting line 43 may be accessed through the connection line maintenance access 23. Preferably the water discharge column 40 is positioned during initial deployment before fish is introduced to the fish tank 1 . Typically, the fish tank 1 is transported to site by a service vessel and deployed. In an initial state the exterior enclosure 2 is not tensioned by the water discharge column 40. This may be referred to as a relaxed state. In this state the water discharge column 40 and the lower utility transition element 111 is supported by the tension lines 20 and / or the lifting line 43. The relaxed state may not be ideal for operation as the exterior enclosure 2 may be prone to cyclic loading due to waves and currents. It is therefore a need to enhance the stability and hydrodynamics of the exterior enclosure 2 by elongating it vertically, which also would expand the tank 1 almost to its full capacity before being pressurized. This may be referred to an expanded state.

[0086] To transition the exterior enclosure between a relaxed state and an expanded state, the connection lines 20 are released and the water discharge column 40 may be lowered to a desired position by the lifting line 43. Care is taken to gently tension the exterior enclosure 2 when lowering the water discharge column 40. The service vessel may have an onboard winch for lowering and hoisting the lifting line 43 and tension sensors connected to the lifting line 43. A decrease in tension of the lifting line 43 indicates that some of the weight is being supported by the exterior enclosure 2. As such, the operator can cease lowering the lifting line 43 when its tension is reduced by a certain degree wherein the exterior enclosure 2 has reached its expanded state. Afterwards, the stopping means 21 secure the connection lines 20 while the lifting line 43 is freed, enabling the weight to shift onto the connection lines 20. Consequently, the connection lines 20 support the lower utility transition element 111 and the water discharge column 40 independently.

[0087] The central column 40 can also be adjusted vertically while the fish tank 1 is in operation. Typically, the fish tank 1 is brought to surface so that the upper utility transition element 110 is at least partly above the waterline. Thereafter, the lifting line 43 is tensioned by means of a winch (not shown) or by manual labour. The lifting line 43 is secured, i.e. fastened to the upper utility transition element 110 by means of e.g. a chain block, a chain hoist, a snap lock, a snap hook, a block & tackle, a shackle or a hook. Securing the lifting line 43 ensures that it takes the weight off the connection lines 20 and the exterior enclosure 2 caused by the central column 40 and lower utility transition element 111. Once done, the connection lines 20 are freed, but the lifting line 43 remains under tension. The lifting line 43 can subsequently be hoisted or lowered and thereafter locked in a desired position. The lifting line 43 is typically operated by a winch on a service vessel, but can also be operated by personnel deployed on a maintenance platform 29 located on the upper utility transition element 110. After the lifting line 43 is locked and secured, the connection lines 20 are tensioned and the lifting line 43 is freed, enabling the weight to shift onto the connection lines 20.

[0088] The exterior enclosure 2 is typically a flexible membrane, and thus when hoisting or lowering the water discharge column 40, the exterior enclosure 2 is shortened and elongated respectively. The ability to lower and hoist the water discharge column 40 makes it possible to adjust the shape of the fish tank 1 along with its exterior enclosure 2. Also, the ability to lower and hoist the water discharge column 40 makes it possible to adjust the load distribution between the connection lines 20 and the exterior enclosure 2.

[0089] The permeable portion 45 may be a mesh or matrix of rope, chain, fabrics, polymers or metal or any other suitable material for making a permeable structure. The mesh width of the permeable portion 45 is typically be adjusted according to required flow conditions. The permeable portion 45 is thereby configured to prevent fish from entering the central water flow and / or to prevent fish from accessing infrastructure 46 within the column 40.

[0090] The water discharge column 40 may comprise at least one intermediate connection line 200 (also referred to as a tether) extending between and connected to the top plate 42 and the non-permeable portion 44. The intermediate connection lines 200 and all other connection lines according to the invention are typically made of at least one of rope, chain, wire and plastics. The intermediate connection lines 200 may also be rigid metal and / or plastic rods. The intermediate connection lines 200 are typically connected substantially along the circumference, i.e. , close to the outer perimeter, of the top plate 42, and to the circumference of the non-permeable portion 44.

[0091] The intermediate connection lines 200 function as a mechanical elongation of connection lines 20, impeding the upper and lower utility transition element from moving apart or towards each other. By tensioning the connection lines 20, the intermediate connection lines 200 are also tensioned. Advantageously, the intermediate connection lines 200 provide large spaces between them to allow a water flow into the centre of the water discharge column 40. In combination with a permeable mesh the permeable portion 45 is kept free of surfaces blocking water flow.

[0092] The intermediate connection lines 200 also serve as a support for the permeable portion 45 forcing it to maintain a substantially cylindrical shape and preventing it from coming into contact with infrastructure 46.

[0093] In aspects the permeable portion 45 may be a rigid / strong permeable structure, such as a rigid cylinder with perforations made of any one of metal, plastics and / or composite materials or a fencing comprising rigid steel rods. The permeable portion 45 may also be a strong flexible mesh structure comprising e.g. a chain mesh. In this embodiment, there is not necessarily a need for intermediate connection lines 200. Such a rigid / strong structure would be self-supporting, extending between and connected to the top plate 42 and the lower non- permeable portion 44 e.g. by means of welding. Such a rigid / strong structure may also completely replace connection lines 200 and the top plate 42.

[0094] In aspects the top plate 42 may have a larger diameter than the non-permeable portion 44, and the permeable portion 45 may have a conical shape. This may be advantageous forcing the fish to swim further away from the tank 1 centre. This prevents waste and excrements from entering the central exiting water flow and encourages waste and excrements to instead sink and gather on top of the lower utility transition element 111.

[0095] The non-permeable portion 44 not only provides support, but it ensures that sludge, excrements, debris, dead fish and other waste is accumulated in the bottom part of the tank and prevents such waste from entering the central exiting water flow through the water discharge column 30. This prevents waste from exiting through the outlet 80.

[0096] Fig. 3 is a cross-sectional perspective view of the housing 28 of the upper utility transition element 110. The housing 28 is seen from the inside at an upwards angle. Fig. 3 show the at least one connection line maintenance access 23 through which the connection lines 20, the lifting line 43 (not shown) and the lines stoppers 21 may be reached. Excess lines of the connection lines 20 and the lifting line 43 may be pulled through the maintenance access 23 and stored at an external location.

[0097] Fig. 4 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention with an alternative water discharge column 40. Unlike the other embodiments, the water discharge column in Fig. 4 lacks a permeable portion and is completely open for water flow. It also comprises at least one connection line 220 (also referred to as a tether) linking the non-permeable portion 44 and the upper utility transition element 110. Hoisting and lowering the column, the lower utility transition element 111 , and the exterior enclosure 2 are carried out in the same manner as the other embodiments.

[0098] Fig. 5 is a cut-out perspective view of the non-permeable portion 44 according to the embodiment of Fig. 4. The water discharge column 40 of Fig. 5 comprises a non-permeable portion 44 and connection lines 220 linking the non-permeable portion 44 and the upper utility transition element 110.

[0099] The connection lines 220 are typically connected substantially along the circumference, i.e. close to the outer perimeter to the circumference of the non- permeable portion 44. The connection lines 220 may also serve as a fence, preventing fish from entering the centre of the water discharge column 40.

[0100] The water discharge column 40 of Fig. 4 may still be equipped with a permeable portion according to the previous embodiments, the permeable portion may extend from the non-permeable portion 44 to the upper utility transition element 110.

[0101] Fig. 6 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention according to an alternative embodiment. In Fig. 6 the rearing tank may comprise all of the components described in Fig. 1-5, except for the connection lines 20 and the stopping means 21 . In this embodiment the water discharge column 40 is suspended merely by at least one lifting line 43 such as a wire, cable, chain or rope. The at least one lifting line 43 is configured to carry the weight of the water discharge column 40, the lower utility transition element 111 and the flexible enclosure 2 alone. The at least one lifting line 43 may be connected to a connection point 22 as previously described.

[0102] By lifting or lowering the lifting line 43, the water discharge column 40 may be adjusted in a simple manner. After adjustment, the adjusting means is locked by using the connection point 22.

[0103] In the embodiment of Fig. 6 the lifting line 43 may in aspects be connected directly to the top plate 42 to a top plate connection point (not shown) or directly to the connection point 441 . The latter aspect results in the embodiment of Fig. 1 without the connection lines 220 and including a rigid permeable portion 45.

[0104] Fig. 7 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention according to the embodiment of Fig. 6 with alternative lifting means.

[0105] In one aspect, the tank 1 is forced downwards by the weight of the lower utility transition element 111 and held floating by means of an external floating device such as a float ring located at the water surface. In addition, the tank may be moored to the seabed. The lowering and hositing / lifting of the water discharge column 40 as described above relates primarily to this aspect.

[0106] In another aspect, the upper utility transition element 110 may comprise floating means such as a buoy or a ballast tank wherein its buoyancy exceeds the weight of the tank 1 , forcing the tank 1 to towards the water surface. Especially in this aspect but not limited to this aspect, the lower utility transition element 111 of the tank 1 is moored to seabed to fix the tank 1 to a desired water depth and / or to prevent the tank 1 from floating up to the water surface.

[0107] In Fig. 7, the upper utility transition element 110 comprises floating means such as a buoy or a ballast tank wherein its buoyancy exceeds the weight of the tank 1 as explained above. The lower utility transition element 111 is typically moored to the seabed.

[0108] In the embodiment of Fig. 7, the lifting line 43, may run through a pulley 700 connected to the top plate 42 and back to the upper utility transition element 110 where it is fixed. Thus, by releasing the lifting line 43 from the connection point 22 and tensioning / pulling the lifting line 43, the water discharge column 40 is moved upwards towards the upper utility transition element 110. This effectively brings the utility transition elements 110 and 111 closed together and thus compresses the tank 1 vertically.

[0109] Fig. 8 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention according to the embodiment of Fig. 1 , 2A, 2B or Fig. 4 including alternative lifting means.

[0110] In Fig. 8, the upper utility transition element 110 comprises floating means such as a buoy or a ballast tank wherein its buoyancy exceeds the weight of the tank 1 as explained above. The lower utility transition element 111 is typically moored to the seabed. The lifting line 43, may run through a pulley 700 connected to the hoist support element 41 and back to the upper utility transition element 110 where it is fixed. Thus, by tensioning / pulling the lifting line 43, the water discharge column 40 is moved towards the upper utility transition element 110. This effectively brings the utility transition elements 110 and 111 closed together and thus compresses the tank 1 vertically. By releasing the lifting line 43 the buoyancy of the utility transition element 110 moves the utility transition elements 110 and 111 away from each other.

[0111] The connection lines 20, 200, 220 may be adjusted and tensioned subsequently after operating the lifting line 43.

[0112] Fig. 9 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention according to the embodiment of Fig. 6 with an integrated winch 701 . In Fig. 9, the upper utility transition element 110 comprises floating means such as a buoy or a ballast tank wherein its buoyancy exceeds the weight of the tank 1 as explained above. The lower utility transition element 111 is typically moored to the seabed. In Fig. 9 a winch 701 is connected to the upper utility transition element 110. The winch 701 operates the lifting line 43 which is connected to the top plate 42.

[0113] The lifting line 43 is operated by the winch 701 so that when the water discharge column 40 is lifted, the upper utility transition element 110 is forced towards the lower utility transition element 111 , effectively compressing the tank 1 . The winch 701 may include stopping means. The lifting line 43 may pass through the connection point 22 which may include stopping means. In order to expand the tank 1 i.e. stretch the tank 1 so that the upper utility transition element 110 moves away from the lower utility transition element 111 , the operator can simply release the line 43 from the winch 701 and / or the connection point 22 in a controlled manner. Fig. 10 is a cross-sectional side view of a submersible fish rearing tank 1 of the present invention according to the embodiment of Fig. 1 , 2A, 2B or Fig. 4 with an integrated winch 701. In Fig. 10, the upper utility transition element 110 comprises floating means such as a buoy or a ballast tank wherein its buoyancy exceeds the weight of the tank 1 as explained above. The lower utility transition element 111 is typically moored to the seabed. The winch 701 may include stopping means. The lifting line 43 may pass through the connection point 22 which may include stopping means.

[0114] In Fig. 10 a winch 701 is connected to the upper utility transition element 110. The winch 701 operates the lifting line 43 which is connected to the hoist support element 41 . By actuating the winch 701 to pull the lifting line 43 the utility transition elements 110 and 111 is moved against each other. By releasing the lifting line 43 the transition elements 110 and 111 is moved away from each other. The connection lines 20, 200, 220 may be adjusted and tensioned subsequently after operating the lifting line 43.

Claims

P A T E N T C L A I M S1 . A submersible fish rearing tank (1 ) comprising: a flexible exterior enclosure (2) forming a closed fish habitat; an upper utility transition element (110); water supply means (30, 30’, 31 , 3T) adapted to pump water into the tank (1 ) to provide a pressure inside the tank (1 ) exceeding a pressure acting on the outside of the tank (1 ); a water outlet (80); a water discharge column (40) configured to guide or transport fluid, the water discharge column (40) in fluid connection with the inner volume of the tank (1 ) and in fluid connection with the water outlet (80); characterized in that wherein the water discharge column (40) comprises a non-permeable portion (44) in connection with the flexible exterior enclosure (2); and wherein the tank (1 ) comprises a lifting line (43) connected to the water discharge column (40) for moving the water discharge column (40) towards the upper utility transition element (110) or moving the water discharge column (40) away from the upper utility transition element (110).

2. The submersible fish rearing tank (1 ) of claim 1 the water discharge column (40) is connected to the upper utility transition element (110) by connection lines (20, 220) extending between the upper utility transition element (110) and the water discharge column (40); and wherein the connection lines (20, 220) are connected to connection line stopping means (21 ).

3. The submersible fish rearing tank (1 ) according to any of the preceding claims, wherein the water discharge column (40) comprises a permeable portion (45) located above the non-permeable portion (44).

4. The submersible fish rearing tank (1 ) according to any of the preceding claims, wherein the water supply means (30, 30’, 31 , 3T) comprises at least one watersupply column (30, 30’) in fluid connection with the tank (1 ), wherein the at least one water supply column (30, 30’) is attached to the exterior enclosure (2) and comprises a pump unit (31).

5. The submersible fish rearing tank (1 ) according to any of the preceding claims, wherein each water supply column (30, 30’) comprises a plurality of water discharge means (122) aligned in a vertical array along a surface of the water supply column (30, 30’), the water discharge means (122) adapted to discharge water in the horizontal plane and / or at an angle relative to a tangential component of the exterior enclosure (2).

6. The submersible fish rearing tank (1 ) according to any of the preceding claims, wherein the upper utility transition element (110) comprises at least one connection line maintenance access (23) through which maintenance personnel may gain access to the connection lines (20, 220) and the lifting line (43).

7. The submersible fish rearing tank (1 ) according to any of the preceding claims 2-4, wherein the permeable portion (45) comprises a mesh made of at least one of rope, yam, chain, fabric or plastic material.

8. The submersible fish rearing tank (1 ) according to claim 7, wherein the water discharge column (40) comprises:- a top plate (42) enclosing its top end portion discharge column (40); and- at least one intermediate connection line (200) located within the permeable portion (45) connected to and extending between the non-permeable portion (44) and the top plate (42);- wherein the connection lines (20) comprises a plurality of connection lines (20) connected to and the extending between the top plate (42) and the upper utility transition element (110).

9. The submersible fish rearing tank (1 ) according claim 8, wherein each intermediate connection line (220) is connected close to the perimeter of the topplate (42) at one end, and close to the perimeter of the non-permeable portion (44) at the other end.

10. The submersible fish rearing tank (1 ) according claim 9, wherein the permeable portion (45) has a conical shape tapered towards the non-permeable portion (44).11 . The submersible fish rearing tank (1 ) according to any of the preceding claims, wherein infrastructure (46) such as pipes, hoses and cables may extend within the water discharge column (40) along a vertical axis.

12. The submersible fish rearing tank (1 ) according to any of the preceding claims, comprising a lifting line connection point (22) connected to the upper utility transition element (110) for suspending the lifting line (43) from the upper utility transition element (110).

13. The submersible fish rearing tank (1 ) according to any of the preceding claims, wherein the lifting line (43) runs from the upper utility transition element (110) through a pulley (700) connected to the water discharge column (40) and back towards the upper utility transition element (110).

14. The submersible fish rearing tank (1 ) according to any of the preceding claims 1 -12, wherein the lifting line (43) is connected to a winch (701 ) connected to the upper utility transition element (110), wherein the lifting line (43) can be operated by the winch (701 ).

15. Method of lifting the water discharge column (40) within the tank (1 ) according to any of the preceding claims, comprising the steps of:- tensioning the lifting line (43) until the water discharge column (40) moves towards the upper utility transition element (110) until it reaches a desired level;- locking the lifting line (43) at a connection point (22).

16. Method of lifting the water discharge column (40) according to any of the preceding claims 2-14, further comprising the steps of:- releasing the stopping means (21 );- tensioning the connection lines (20, 200, 220);- locking the stopping means (21 ).

17. Method of lowering the water discharge column (40) within the tank (1 ) according to any of the preceding claims 1-14:- releasing the lifting line (43) until the water discharge column (40) moved away from the upper utility transition element (110) until it reaches a desired level;- fixing the lifting line (43) at a connection point (22).

18. Method of lowering the water discharge column (40) according to any of the preceding claims 2-14, further comprising the steps of:- tensioning the lifting line (43);- releasing the connection lines (20, 200, 220) from the stopping means (21);- locking the stopping means (21 ).

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