NO347173B1

NO347173B1 - Self-stabilizing submersible fish farm

Info

Publication number: NO347173B1
Application number: NO20220816A
Authority: NO
Inventors: Erlend Eide; Sondre Eide
Original assignee: Eide Fjordbruk As
Priority date: 2021-12-10
Filing date: 2022-07-22
Publication date: 2023-06-19
Also published as: NO20220816A1; NO20220935A1; NO20220941A1

Description

Self-stabilizing submersible fish farm

Field of the invention

The present invention relates to a self-stabilizing, closed and submersible fish farm.

Background

One of the goals of the aquaculture industry is environmentally sustainable development. The industry is therefore producing solutions that achieve energy efficiency, reduction of fossil fuels and reduced climate footprint.

The spread of salmon lice and other disease infections is a major issue for the aquaculture industry. Escape of fish is also a problem especially for the wild salmon stock - and is often due to technical failure, incorrect use of equipment and vessels, or storms.

In addition, emissions in the aquaculture industry have increased, and the industry accounts for large amounts of seabed waste along coastal areas. The waste largely consists of waste from feed and faeces, but also waste from medical treatments and delousing. The environmental impact because of the waste is largest below or in the immediate vicinity of the fish farms, and the discharges could potentially affect life on the seabed and affect the environmental conditions near the sites.

The above-mentioned issues create a need for closed fish farms that reduce the environmental problems, and which ensure growth and sustainability in the future. To increase production, there is also a need for new locations in more weatherexposed areas at sea. Closed and semi-closed fish farms have been deployed to remedy the above problems. Some companies produce land-based facilities, but such plants require considerable land areas, increased energy and water consumption. Handling of sludge production yield significant costs. Rigid fish tank structures are also costly to produce, and large tanks may be extremely heavy and hard to transport and deploy.

It is therefore an object of the invention to provide an easy to transport, energy efficient, closed, submersible fish rearing facility with low weight and that is cost efficient, easy to deploy and easy to maintain.

The environment from which the fish is sought to be separated from, is mainly the upper water layer to avoid lice and other pathogens, while the waste substances are released into the bottom as in traditional cages. Disadvantages of these solutions include that they are cumbersome to operate, and they do not sufficiently reduce seabed pollution.

It is also an object of the invention to provide a facility that is adapted to be submerged below the upper water layers of the sea to avoid sea-lice, harsh weather conditions and floating debris.

Fish farms are prone to harsh weather conditions such as waves and currents. Submerged fish farms are therefore subjected forces which may rotate, tilt and slant the fish farm creating an unstable habitat for the fish. Therefore, fish farms are moored topside and/or from seabed. The mooring systems are expensive and requires regular maintenance.

Submersible and closed fish farms are often reliant on gases such as air and oxygen creating gas bubbles within the fish farms. Gas bubbles may be trapped inside the fish reservoir e.g. at a transition section between the mid-section and the top-section. This may create a large gas pocket creating an offset, and relocating the buoyancy centre of the fish farms, causing the fish farm to tilt dramatically. It is a very complicated process to drain such a gas pocket during operation. If the reservoir is penetrated to release the gas, fish may escape, and it may be hard to repair the opening during operation. If the reservoir is tilted with the use of mooring lines, the reservoir is subjected to tension which may damage the structure.

Finally, it is an object of the invention to provide a submersible and closed fish farm which is self-stabilizing, preventing the fish farm from tilting as a result of waves, currents and other forces. Also, it is an object of the invention provide a submersible and closed fish farm which does not accumulate gas pockets in locations distal to the centre axis of the fish reservoir.

GB2577454A relates to a cage with a tubular unit provided with two floats that are dipped into water. The tubular unit is connected with an upper sleeve. A steel cable is fixed in an upper edge of the tubular unit. The tubular unit is connected with two lifting units that are located centrally on a bottom of the tubular unit. An outer surface of the tubular unit is fixed with perimeter rings that are connected with the steel cable, where the steel cable is made of high-strength polyethylene and the tubular unit is made of polymer with high mechanical strength and low biofouling adhesion.

Summary of the invention

The invention relates to a submersible fish rearing tank including an exterior enclosure, an upper utility transition element providing a transition for at least one of a water inlet, a water outlet, a gas outlet, an air inlet, and connections for instrumentation, fixed to the exterior enclosure. The upper utility transition element may have a buoyancy element. The upper utility transition element is located at a top centre of the fish rearing tank, and the upper utility transition element includes an internal fluid reservoir for accumulating gas emerging within the tank, and wherein the tank has a conical top-section.

The invention relates to said tank wherein the conical-top section is tapered towards the upper utility transition element at an angle, wherein the angle is larger than the tank’s tilt angle.

The invention relates to said tank wherein the. conical-top section is tapered towards the upper utility transition element at an angle above 10 degrees, preferably 15 degrees.

The invention relates to said tank wherein the fluid reservoir includes at least one fluid outlet located at a lower part of the fluid reservoir for releasing a fluid from the fluid reservoir.

The submersible fish rearing tank may further include a water supply means adapted to pump water into the submersible fish rearing tank to provide a pressure inside the submersible fish rearing tank exceeding a pressure acting on the outside of the submersible fish rearing tank, wherein the water supply means includes at least one inlet water supply column with nozzles adapted to provide water into the submersible fish rearing tank fixed in relation to the exterior enclosure and at least one pump unit, adapted to pump water into the tank through the water supply column via the nozzles.

The submersible fish rearing tank may further include a lower utility transition element with a water outlet, and the lower utility transition element may be located at a bottom centre of the fish rearing tank.

The submersible fish rearing tank may further include a weight element located at a bottom of the fish rearing tank.

The weight element may form a part of the lower utility transition element.

The invention relates to said tank further including a central column extending along a central axis of the tank between the upper utility transition element and the lower utility transition element.

The invention relates to said tank further including a flexible connection element extending along a central axis of the tank between the upper utility transition element and the lower utility transition element.

The invention relates to said tank wherein the exterior enclosure is made of a flexible material.

The invention relates to said tank including two tubular inlet water supply columns located diametrically opposite to each other.

The invention relates to said tank further including a flow restriction or throttle to reduce or completely close the outlet water flow from the central column outlet to maintain the pressure inside the submersible fish rearing tank above the pressure acting on the outside of the submersible fish rearing tank.

The invention relates to said tank further including a ballast and/or an adjustable buoyancy element to orient and maintain the buoyancy of the submersible fish rearing tank.

Brief description of drawings

Fig. 1 is a cross-sectional side view of a submersible fish farm according to the invention;

Fig. 2 is a transparent perspective view of the fish farm according to the invention; Fig. 3 is a cross-sectional side view of the fish farm according to Fig.1 in an alternative embodiment;

Fig. 4 is a cross-sectional side view of the fish farm according to Fig.1 in an alternative embodiment;

Fig. 5 is a cross-sectional side view of an upper part of the fish farm according to the invention; and

Fig. 6 is a cross-sectional perspective view of an upper part of the fish farm according to the invention seen from below; and

Fig. 7 is a side view of the fish farm according to the invention in a tilted state.

Detailed description of embodiments

Fig. 1 is a cross-sectional side view of a submersible fish farm according to the invention deployed in water. The submersible fish farm includes an underwater fish rearing tank 100.

The tank 100 further includes an exterior enclosure 17, an upper utility transition element 110 and a lower utility transition element 111 forming a closed habitat for fish. The upper utility transition element 110 includes a support collar 702 and a fluid reservoir 700 in fluid communication with the tank 100. The fluid reservoir 700 is fixed to and supported by the support collar 702. The exterior enclosure 17 is fixed to the circumference of the support collar 702. The exterior enclosure may also be fixed to the lower utility transition element 111.

The habitat is sufficiently closed to allow a pressure to build up inside the tank. The internal hydrodynamic pressure forces the exterior enclosure 17 to maintain its shape as illustrated in Fig.1 during operation.

The exterior enclosure 17 is preferably a membrane made of a flexible material such as PE, PVC, latex, nylon or any impermeable or semi-permeable, flexible plastic or fabric material. The exterior enclosure 17 may also be made of a rigid material forming a rigid tank structure.

Although the tank 100 is closed, the tank 100 may receive seawater (fresh or saline), fluids such as air and oxygen, and feed, and furthermore discharge used water and waste.

The term “closed” used in this application does not exclude the presence of inlets and outlets, but is used to distinguish the invention from fish farms with permeable net cages, open-air basins etc.

Intake and discharge may be autonomously controlled by a controller 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.

Incoming and outgoing water may be filtered to prevent sea lice from entering the tank 100, and from polluting the surrounding environment, although the tank water may be replaced in such a rate that sea lice would not be able to latch on to the fish.

The exterior enclosure 17 is fixed to upper the 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.

The exterior enclosure 17 may be equipped with a zipper (not shown) for opening the enclosure 17 for accessing the inside of the tank 100, e.g. for cleaning, replacing or performing maintenance on internal components.

The submersible fish farm may be deployed and operated offshore, in coastal areas or in freshwater lakes.

Fig. 1 further shows that the underwater fish rearing tank 100 includes a first water supply column 103 and a second water supply column 103’ attached to the exterior enclosure 17 on diametrically opposite sides. Each water supply column 103, 103’ can be a rigid or flexible tubular, elongated structure, preferably cylindrical but may have a rectangular or elliptical cross-section, extending vertically along the exterior of the tank 100 in parallel with the vertical centre axis Z1 of the tank 100. The first water supply column 103 and a second water supply column 103’ attached to the exterior enclosure 17 may be curved to accommodate the shape of the submersible fish rearing tank 100 and may be integrated into a wall exterior enclosure 17.

The tank 100 may include additional water supply columns (not shown) attached to the exterior enclosure 17, preferably having the same circumferential distance between each other. The water supply columns 103, 103’ are preferably made of a light-weight and rigid or flexible plastic or metal material. Suitable materials include PE, PVC, latex, nylon or any impermeable and flexible plastic or fabric material.

The submersible tank 100 may be anchored to a float ring (not shown) and/or moored to the seabed. The submersible tank is prone to currents, waves and other types of loading imposing rotational forces which may momentarily tilt/roll the tank 100 out of any upright position.

The utility transition element 110 includes a buoyancy element 850, such as a dynamic ballast tank, keeping the tank afloat at a desirable depth. In Fig.1 the buoyancy element 850 is a ring-shaped ballast tank providing a buoyancy centre aligned with the centre axis Z1. The buoyancy element 850 may be any conventional buoyancy element providing buoyancy in the top centre of the fish farm.

The tank 100 is therefore not reliant on buoyancy from the fluid reservoir 700, although the fluid 700 reservoir may impose some buoyancy on the fish farm. The lower utility transition element 111 includes a weight element (113), such as a heavy solid material. The upper utility transition element 110 provides buoyancy while the lower utility transition element provides gravity, counteracting any tilting movement and ensures that the tank always returns to an upright position aligned in parallel with a vertical axis Z1.

In Fig.1, the upper utility transition element 110 is coupled with the lower utility transition element 111 via the flexible enclosure 17 thereby providing a submersible spar structure.

Each water supply column 103, 103’ is attached and sealed onto the outside of the exterior enclosure 17 by ways of being sown, glued or melted into the exterior enclosure 17 over an attachment length. In operation, the attachment length is shorter than the distance between the utility transition elements 110, 111.

Consequently, as shown in Fig.1, the exterior enclosure 17 forms a cylindrical mid-section along the said attachment length, a conical top-section and a conical bottom-section. At least one hole in the exterior enclosure 17 is provided to ensure fluid communication between each water supply column 103 and the tank 100 volume.

The conical top-section may also be formed merely by the shape of the exterior enclosure 17 and the tank 100 is not reliant on the water supply columns 103, 103’ to obtain a conical top-section.

The conical top-section of the exterior enclosure 17 is tapered towards the support collar 702 and towards the lower end of the fluid reservoir 700 at an angle A1. The top part of the exterior enclosure 17 is substantially conical but may also have a slightly convex or concave form. The angle A1 may be 1-89 degrees, preferably 10-30 degrees, more preferably 15 degrees. The support collar 702 is conical and is tapered towards the lower end of the fluid reservoir 700 and may have an angle approximately equal to A1 or higher than A1.

An advantage of the conical bottom-section is that its inclination will cause debris and dead fish to slide downwards and accumulate on top of the lower utility transition element 111 from where it will be extracted, preventing accumulation of debris and dead fish in corners of the tank 100 which may be difficult to remove.

The tank 100 provides a submersible fish habitat for rearing fish. Air and gas may be injected into the tank 100 for various reasons including providing an air source to the fish, oxygenizing the habitat and otherwise manipulating the internal water volume. Gas bubbles therefore emerge inside the tank floating upwards.

The upper utility transition element 110 includes a fluid reservoir 700 in fluid communication with the tank 100. Gas emerging inside the tank 100 therefore drifts upwards towards the upper utility transition element 110 into the fluid reservoir 700. The gas is thereby trapped within the upper centre part of fluid reservoir 700.

If the tank 100 is dramatically tilted, gas may be trapped at the transition between the cylindrical mid-section and the top-section of the tank 100. Therefore the gas is prevented from moving towards the centre of the tank 100 towards the fluid reservoir 700. As a result, the tank 100 may experience uncontrolled buoyancy because the trapped gas cannot easily be removed or regulated. Also, the tank 100 is tilted because the buoyancy centre is displaced away from the centre axis Z1 of the tank 100. This is highly undesirable.

Therefore, the conical top-section is provided. The conical top-section prevents the above-mentioned problems by ensuring that any gas inside the tank is accumulated in the fluid reservoir 700 at the top centre, and not in any other location within the tank 100. Gas bubbles within the tank may drift upwards directly into the fluid reservoir 700, or towards the conical ceiling of the tank 100. The conical shaped ceiling will guide the gas bubbles towards the fluid reservoir 700 where the gas is accumulated.

The angle A1 is adjusted according to a tilt allowance limit for the fish farm, i.e. if the maximum tilt allowance limit is 10 degrees, A1 is set equal or larger than 10 degrees. Preferably A1 includes a safety margin such as 3-10 degrees above the tilt allowance limit, preferably 5 degrees. The tilt angle A2 of the tank 100 is shown in Fig.7.

Fish residing in the tank may be prevented from entering the fluid reservoir 700. Furthermore, the fish may be denied access to the internal water line inside the fluid reservoir 700 by means of a permeable barrier (not shown) at the bottom end of the upper utility transition element 110. The fish is thereby trained to consume air dispensed within the tank 100 and not to rely on an artificial waterline within the tank 100.

At least one fluid outlet 701 is provided at a lower part of the fluid reservoir 700. Alternatively, or additionally, at least one fluid outlet 701 may be provided in the top part of the fluid reservoir 700 (not shown). The fluid outlet 701 is configured to ventilate the fluid reservoir and ensures that a waterline is not formed below the fluid reservoir 700, thereby ensuring that the tank volume 100 has no waterline. This is advantageous in that gas is only accumulated in proximity to the centre axis of the tank 100, providing increased stability to the tank 100.

The cross-sectional profile of the fluid outlets 701 may be of any shape, preferably tubular, rectangular or elliptical in cross-section. Each fluid outlet 701 may be connected to a regulating valve (not shown) which can be controlled from topside.

Each fluid outlet 701 provides an opening through which both air and water may pass. In operation, it is an important aspect to maintain a higher pressure inside the tank 100 than outside the tank 100. The fluid outlets 701 are scaled relative to the tank volume, and their cross-sectional area are so small that water may pass through them without significantly affecting the hydrodynamic or hydrostatic pressure within the tank.

The fluid outlets 701 are preferably placed at several locations at the same height with respect to the centre axis Z1, with an equal radial distance between them. Preferably at least three fluid outlets 701 are present with an angle of 120 degrees between them, more preferably four fluid outlets are provided with an angle of 90 degrees between them. This ensures that the fluid reservoir 700 is instantly ventilated regardless of which way the tank 100 is tilted.

Gas will naturally pass through the fluid outlets 701 easier and at a much faster rate than water. Therefore, the fluid outlets 701 will instantaneously submerge if a waterline momentarily drops below the fluid outlets 701 if e.g. the tank 100 is quickly and heavily tilted.

Each water supply column 103, 103’ may include a lower water inlet pump unit 101 located on its lower end. Each water supply column 103, 103’ may also include an upper water inlet pump unit (not shown). Each water inlet pump unit 101 includes a water inlet and a water pump mechanism for drawing clean ambient water into the water supply column 103 and into the underwater fish rearing tank 100 via nozzles 122 in the water supply column 103 with nozzle outlets inside the tank 100. The pump may be actuated by a topside controller (not shown) manually or autonomously based on data retrieved from sensors included in the tank 100. The lower water inlet pump unit 101 serves to increase hydrodynamical pressure within the tank and to create a rotational fluid flow inside the tank 100 and allow water replacement so that the fish is provided with clean water.

The lower utility transition element 111 includes a water outlet 112 for discharging water from the tank 100.

The water outlet 112 may include a passive or actuatable flow restrictor/reducer or throttle to reduce or restrict or completely close the outlet water flow from the water outlet 112 to adjust and maintain the pressure inside the submersible fish rearing tank 100 above the pressure acting on the outside of the submersible fish rearing tank 100.

The pressure difference between the outside and the inside of the tank allows the water outlet 112 to passively expel water from inside the tank 100.

The tank 100 includes a plurality of upper light sources (not shown) attached to the inside of the utility transition element 110. The tank 100 may also include a plurality of lower light sources (not shown) attached the lower utility transition element 111.

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, fixed to the exterior enclosure 17.

Fig. 2 is a transparent perspective view of the fish farm according to the invention. Fig. 2 shows the centre axis Z1 of the fish farm. The upper utility transition element 110 is located at the top of the tank 100, and the lower utility transition element 111 is located at the bottom end top the tank 100. The utility transition elements 110, 111 are centred with respect to the centre axis Z1.

Each water supply column 103, 103’ includes nozzles 122 aligned vertically along a surface of the water supply column 103, 103’. The nozzles 122 have outlets inside of the tank 100. The nozzles 122 are oriented at an angle with a tangential component to create rotational flow inside the tank. The nozzles 122 of each of the supply columns 103, 103’ may be oriented in the same direction to create the rotational flow inside the tank. The nozzles 122 may also be aimed in different directions to create a desired rotational flow inside the tank.

The lower part of the tank may not include water supply nozzles to reduce flow and to allow faeces and dead fish settle at the bottom for removal.

The fluid reservoir 700 forms a fluid volume symmetrical about the centre axis Z1. Gas trapped in the fluid reservoir 700 will impose some buoyancy on the tank 100, and the location of the fluid reservoir 700 ensures that the buoyancy imposed is centred with respect to the centre axis Z1.

Fig. 3 is a cross-sectional side view of the fish farm according to Fig.1 in an alternative embodiment. The underwater fish rearing tank 100 may in an embodiment further comprise a rigid central column 120 inside the tank 100. The central column 120, which is connected to and extending between the upper utility transition element 110 and the lower utility transition element 111, may be cylindrical and oriented vertically along the vertical centre axis of the tank 100. The central column 120 advantageously also acts as a support column and a connection element between the upper utility transition element 110 and the lower utility transition element 111. The central column 120 absorbs both pressure and tension and maintains a fixed distance between the upper utility transition element 110 and the lower utility transition element 111, thereby relieving the external enclosures 17 from tension and ensuring that the tank 100 maintains its shape.

The tank 100 may include one or several auxiliary sensors (not shown) attached to the central column 120. Auxiliary sensors may be located on any rigid internal component of the tank 100 measuring water quality parameters such as oxygen level, temperature, pressure, visibility, and any other parameter relevant for fish rearing conditions. The sensors may pass data to a topside controller which may accordingly adjust inflow and outflow of water. A drop in the internal water pressure may indicate leakage or malfunctioning pumps which may signal a warning to personnel.

The utility transition elements 110, 111 provides connections and bases for the various utilities.

The upper utility transition element 110, the lower utility transition element 111 and the central column 120 act as a submersible spar structure.

Fig. 4 is a cross-sectional side view of the fish farm according to Fig.1 in an alternative embodiment. In Fig.4 the tank 100 is provided with a flexible connection element 711 connected to and extending between the upper utility transition element 110 and the lower utility transition element 111. The flexible connection element 711 may be a single or a plurality of a chain, a wire, a line, or a rope. The flexible connection element 711 may be tubular. The flexible connection element 711 is advantageous compared to a rigid structure in that it is light weight and simple to assemble. The flexible connection element 711 may absorb tension and prevent the utility transition elements 110, 111 from moving away from each other, thereby reducing the diameter of the tank 100.

The upper utility transition element 110, the lower utility transition element 110 and the flexible connection element 711 act as a submersible spar structure.

Fig. 5 is a cross-sectional side view of an upper part of the fish farm according to the invention. Fig.5 shows the upper utility transition element 110 the conical top part of the tank 100. In Fig.5 the conical top-part is slightly curved at a tank edge 780 i.e. the transition between the cylindrical part and the conical top-section. Fig. 5 shows that the angle of the support collar 702 and the conical top-section is substantially equal. The support collar thereby acts as an extension of the upper conical part of the exterior enclosure 17. The fluid outlets 701 of the fluid reservoir 700 are also shown in Fig.5. The buoyancy element connected to the upper utility transition element 110 is not shown in Fig.5.

Fig. 6 is a cut-out perspective view of an upper part of the fish farm according to the invention seen from below. Fig.6 shows the bottom surface of the support collar 702. Fig.6 also shows the fluid outlets 701 of the fluid reservoir 700. The buoyancy element connected to the upper utility transition element 110 is not shown in Fig.5.

Fig. 7 is a side view of the fish farm according to the invention in a tilted state. Fig. 7 shows the vertical axis Z0 which is perpendicular to the sea level. When the tank 100 is tilted due to e.g. waves or currents, the tank 100 is tilted relative to the Z0 axis. The tilt angle A2 is the angle between the centre axis of the tank Z1 and the vertical centre axis Z0.

Claims

P ATENT C LAIMS

1. A submersible fish rearing tank (100) comprising:

an exterior enclosure (17);

an upper utility transition element (110) providing a transition for at least one of a water inlet, a water outlet, a gas outlet, an air inlet, and connections for instrumentation, fixed to the exterior enclosure (17);

wherein the upper utility transition element (110) comprises a buoyancy element (850);

wherein the upper utility transition element (110) is located at a top centre of the fish rearing tank (100), and

wherein the upper utility transition element (110) comprises an internal fluid reservoir (700) for accumulating gas emerging within the tank (100); and wherein the tank (100) has a top section which is tapered towards the fluid reservoir (700).

2. The submersible fish rearing tank (100) of claim 1, wherein the top section is conical.

3. The submersible fish rearing tank (100) of claim 1 or 2 wherein the top section is tapered towards the upper utility transition element (110) at an angle (A1), wherein the angle (A1) is larger than the tank’s tilt angle (A2).

4. The submersible fish rearing tank (100) of claim 2 or 3, wherein the top section is tapered towards the upper utility transition element (110) at an angle (A1) above 10 degrees, preferably 15 degrees.

5. The submersible fish rearing tank (100) of any preceding claim, wherein the fluid reservoir (700) includes at least one fluid outlet (701) for releasing a fluid from the fluid reservoir (700).

6. The submersible fish rearing tank (100) of claim 5, further comprising:

water supply means (103, 101) adapted to pump water into the submersible fish rearing tank (100) to provide a pressure inside the submersible fish rearing tank (100) exceeding a pressure acting on the outside of the submersible fish rearing tank (100), wherein the water supply means (103, 101) comprises at least one inlet water supply column (103) with nozzles (122) adapted to provide water into the submersible fish rearing tank (100) fixed in relation to the exterior enclosure (17) and at least one pump unit (101) adapted to pump water into the tank (100) through the water supply column (103) via the nozzles (122).

7. The submersible fish rearing tank (100) of claim any of the preceding claims, further comprising:

a lower utility transition element (111) including a water outlet (112), wherein the lower utility transition element (111) is located at a bottom centre of the fish rearing tank (100).

8. The submersible fish rearing tank (100) of any preceding claims, further including, a weight element (113) located at a bottom of the fish rearing tank (100).

9. The submersible fish rearing tank (100) of claims 7 and 8, wherein the weight element (113) forms a part of the lower utility transition element (111).

10. The submersible fish rearing tank (100) of any preceding claim, further comprising a central column (120) extending along a central axis of the tank (100) between the upper utility transition element (110) and the lower utility transition element (111).

11. The submersible fish rearing tank (100) of any preceding claim 1-6, further comprising a flexible connection element (711) extending along a central axis of the tank (100) between the upper utility transition element (110) and the lower utility transition element (111).

12. The submersible fish rearing tank of claim 1, wherein the exterior enclosure (17) is made of a flexible material.

13. The submersible fish rearing tank of any preceding claim, comprising two tubular inlet water supply columns (103, 103’) located diametrically opposite to each other.

14. The submersible fish rearing tank of any of the preceding claims, further including a flow restriction or throttle (153) to reduce or completely close the outlet water flow from the central column outlet (152) to maintain the pressure inside the submersible fish rearing tank (100) above the pressure acting on the outside of the submersible fish rearing tank (100).

15. The submersible fish rearing tank of any of the preceding claims further including a ballast and/or an adjustable buoyancy element to orient and maintain the buoyancy of the submersible fish rearing tank (100).