WO2023140741A1

WO2023140741A1 - Fish farm concept

Info

Publication number: WO2023140741A1
Application number: PCT/NO2023/050011
Authority: WO
Inventors: Øyvind Høie
Original assignee: Brim Farm IPR AS
Priority date: 2022-01-19
Filing date: 2023-01-18
Publication date: 2023-07-27
Also published as: NO20220063A1; NO347069B1

Abstract

The invention provides a fish farm concept, comprising a tank and a collar,wherein the tank is arranged inside the collar; the tank comprises waterimpermeable side structure and a water impermeable bottom wall; the fish farmconcept further comprises at least one water inlet to the tank and one wateroutlet from the tank. The fish farm concept is distinguished in that: the tank comprises a double bottom wall, with one or morecompartments between the double walled bottom and inside the side structure,wherein one or more of the compartments can be ballasted and de-ballasted byoperating a connected pump and piping,wherein the tank in a fish farming mode is arranged in a lower positioninside the collar, and wherein the tank in a transport-cleaning mode is empty forwater and is arranged in a higher position inside the collar, andwherein the collar is a floating structure with buoyancy at least sufficientto carry the weight of the full, partly full or empty tank and provide sufficientsupport to stabilize the tank in the higher position, in the transport-cleaningmode position wherein the tank is capable to be emptied for water by naturalgravitation, without pumping water from the tank, with all or some of the doublebottom ballast compartments de-ballasted, and with the tank empty for waterand all compartments in the double bottom empty or near empty for water, thetank, by natural effects of buoyancy and gravity, is capable to be moved into thetransport-cleaning mode position.Fig. 2.

Description

FISH FARM CONCEPT

Technical Field

The present invention relates to fish farming in general and farming of salmon or other species in the salmonid fish family in particular. More specifically, the invention relates to a concept reducing or removing most or virtually all issues with respect to pollution, salmon lice, mortality, adaptations to increasingly stricter regulations, and more, as will be described further below.

Background Art

The fish farming industry and in particular the salmon and trout farming industry has grown to a very significant industry in Norway and several other countries. However, the growth has not come without challenges; salmon lice, stress reactions of the fish, poisonous algae or other organisms killing the fish, extensive local pollution by faeces and surplus food, shorter growing season than ideal, fish escape from the pens and increasingly strict regulations by the authorities are some severe issues for the fish farmers. As a result, a mortality of about 15% is normal in the salmon farming industry, far above what would be acceptable for farms breeding animals on land.

Currently the industry expands in direction offshore and on locations on land. However, concepts used for the expansion to more remote locations offshore in general results in spreading and increasing the underlying problems of the industry.

Patent publications NO343380 B1 , N020172017 A1 , WO2020229631 A1 and NO332341 B1 represent relevant art. None of said publications include description or illustrations of a fish farm concept with a tank inside a floating collar, wherein the tank can be lifted to an upper position inside the collar and lowered to a lowest position inside the collar, without specific lifting means, or description of why such functionality can be an advantage. A fish farm concept feasible for salmon farming in particular and other salmonoids or fish species in general, reducing or eliminating many or all of the problems briefly mentioned above would be required to meet an urgent demand.

Summary of invention

The present invention provides a fish farm concept reducing or eliminating many or all of the problems addressed.

More specifically, the invention provides a fish farm concept that can be termed a semi-closed fish farm concept, comprising a tank and a collar, wherein the tank is arranged inside the collar; the tank comprises water impermeable side structure and a water impermeable bottom wall; the fish farm concept further comprises at least one water inlet to the tank and one water outlet from the tank. The fish farm concept is distinguished in that: the tank comprises a double bottom wall, with one or more compartments between the double walled bottom and inside the side structure, wherein one or more of the compartments can be ballasted and de-ballasted by operating a connected pump and piping, wherein the tank in a fish farming mode is arranged in a lower position inside the collar, and wherein the tank in a transport-cleaning mode is empty for water and is arranged in a higher position inside the collar, and wherein the collar is a floating structure with buoyancy at least sufficient to carry the weight of the full, partly full or empty tank and provide sufficient support to stabilize the tank in the higher position, in the transport-cleaning mode position wherein the tank is capable to be emptied for water by natural gravitation, without pumping water from the tank, with all or some of the double bottom ballast compartments de-ballasted, and with the tank empty for water and all compartments in the double bottom empty or near empty for water, the tank, by natural effects of buoyancy and gravity, is capable to be moved into the transport-cleaning mode position.

Preferably, the fish farm concept comprises damping material or -structure, preferably at least arranged between the tank and the collar. The damping material or -structure, such as elastomeric based and/or spring based and/or fiber-cloth based-, or other feasible damping material or -structure, reduces the structural and mechanical stress levels when the tank is arranged in a lower position, in the fish farming mode, and/or when the tank is arranged in a higher position, in the transport-cleaning mode. Preferably, the tank comprises a flange and the collar comprises a seat, wherein elastomeric based and/or spring based and/or fiber-cloth based-, or other feasible damping material or - structure is arranged between the flange and the seat, damping transient movements and wave movements, including harmonic wave movements, thereby reducing the structural stress level and the stress level of fish in the tank and enabling scaling up the size of the fish farm without meeting serious stress-strain related structural problems. The fish farm concept preferably also comprises damping material arranged around seawater lines or any ducts arranged on the outside of the tank, in slots in the collar, preferably shaped as fenders around the seawater lines or ducts at and near the two positions: the fish farming mode position, that preferably is the lowermost position of the tank in the collar, and the transport-cleaning mode position, that preferably is the highest position of the tank in the collar with the fish farm concept floating on the sea.

The two extreme positions of the tank of the fish farm are the fish farming mode position, that is the lowermost position of the tank in the collar, and the transport-cleaning mode position, that is the highest position of the tank in the collar with the fish farm concept floating on the sea. A position locking structure, locking the tank in one or each respective extreme position, and optionally further positions, preferably still with damping, is preferably included. In fish farming mode, the tank preferably has negative buoyancy, as will be clear from the further description, which provides sufficient position control in most locations that are not exposed to extreme waves, currents or winds, such as in inshore waters in general.

The fish farm preferably comprises a pump room with one or more pumps as one of the compartments between the double bottom walls, wherein seawater being pumped up to the tank is directed from one or more seawater pumps located in the pump room and/or in one or more vertical ducts welded to the outside of the tank and/or in a recessed room or -area in the collar. With the tanks in the fish farming mode position, the pumps in the vertical ducts and/or in a recessed room or -area in the collar, preferably is below outside sea level and is preferably used for pumping, since seawater flows at least up to the level of the pumps, and the lifting height and energy consumption are minimized. With the tanks in the transport-cleaning mode position, the pumps in the pump rooms must be used, alone or together with further pumps.

Preferably, the fish farm further comprises one (or more) vertical duct(s) welded to the outside of the farm tank and extending from the bottom of the tank to the top of the tank. The duct(s) serves as parts of sea water intakes and secures intake of fresh sea water to be supplied to the farm tank. The collar is shaped correspondingly to allow the duct (s) to pass through the collar to the top of the tank. The duct(s) may protect inside seawater lines, other lines and equipment during hoisting and lowering of the tank. Preferably, there is no direct contact between the duct and the collar and indirect contact only at the fish farming mode position and transport-cleaning mode position via fenders or similar damping structure. In some embodiments, sea water circulation pump(s) is arranged inside the duct(s), and/or air ventilation pipes from the ballast tanks, to allow unobstructed and free ventilation of the ballast tanks to open air at the top of the tank.

In some preferable embodiments, the collar comprises one or more seawater pumps in recesses at elevation below the elevation of the surrounding seawater level in fish farming mode, coupled to seawater lines with intake opening at required depth. Reduced energy consumption with the fish farm concept in the fish farming mode is a beneficial result, since the lifting height is minimized. Simplified access to seawater pumps is also provided. The fish farm concept is assumed to be near 100% in the fish farming mode during operation, allowing energy saving near 100% of the time in operation.

Preferably, the tank comprises a central vertical structure, termed a cigar, which cigar is a combined water outlet from the tank and an access channel from above sea level to the pump room, wherein a vertical water outlet section is perforated from a suitable elevation above the double bottom wall and up to the water surface in the tank as filled almost fully with water in a farming position, and a vertical access section of the cigar is a dry and safe access channel for personnel down to the pump room. The cigar comprises a vertical watertight bulkhead extending from top to bottom and dividing the structure in two compartments. The vertical water outlet section is perforated from an elevation above the double bottom where the cigar meets the upper wall of the double bottom, and up to, or about 1 to 2 m below, the water surface in the tank as almost filled fully with water in a fish farming position. Preferably, the water outlet section of the cigar will be secured with a double barrier system to safeguard the fish integrity of the tank. The vertical access section of the cigar also allows safe location for and access to other equipment for the operation of the farm tank. The central vertical structure, termed a cigar, which cigar is a combined water outlet from the tank and an access channel from above sea level to the pump room, as described above and illustrated, is feasible also for other fish farm concepts, and is an invention per se, representing an independent invention provided in addition to the fish farm concept of the present invention.

Preferably, the pump room is arranged concentrically around the cigar in the double bottom of the tank. Preferably all compartments around the pump room within the double bottom are for ballast or de-ballasting by filling or emptying for water by operating one or more ballast pumps in the pump room with connected piping and valves. Preferably, the tank can be emptied for water by natural gravitation, without pumping water from the tank, with all or some of the double bottom ballast compartments de-ballasted. With the tank empty for water and all compartments in the double bottom empty or near empty for water, the tank, by natural effects of buoyancy and gravity, moves into a transport-cleaning mode position, where the tank preferably can be locked to the collar, preferably with damping, for safe towing from for example a yard to a farming location or within the area where the farmer has permission to operate, facilitating the transport while spending a minimum of the structural capacity of the fish farm. Also, internal and external cleaning of the tank is facilitated by placing the tank in the transport-cleaning mode position.

Preferably, the tank has negative buoyancy in the farming mode position, with a water level inside the tank higher than the water level of the surrounding sea, thus creating overpressure in the water in the tank, whereby water flows out from the tank without pumping, through a cigar as described above or through another outlet. In the farming mode position, the collar carries the weight of the tank. The result is significantly reduced movements compared to if the tank and collar were single independent units, providing increased stability and beneficial effects for the fish stress, health and growth, especially with damping between tank and collar.

The fish farm preferably further comprises a water penetrable constriction structure that can be arranged from top of the tank in downward direction until the tank has been emptied for fish. Preferably, the constriction structure comprises two ring structures, one outer ring structure just smaller than the inner diameter or dimension of the tank and one inner ring or structure just larger than the cigar structure, with a net or grate structure in between the ring structures, wherein the tank comprises an outlet for fish, towards which outlet fish is directed by the constriction structure. In principle, the constriction structure is only used for, and preferably is immersed into the tank only when fish are to be unloaded from the tank. The constriction may preferably include rollers to smoothly slide against the steel bulkheads and with brushes fitted to secure that the gap between the rings and the structure is sealed for hindering fish from passing through the openings during unloading. The water penetrable constriction structure that can be arranged from top of the tank in downward direction until the tank has been emptied for fish, as described above and illustrated herein, is useful also for other fish farm concepts, and is an invention per se, representing an independent invention provided in addition to the fish farm concept of the present invention.

The fish farm preferably further comprises a faeces-surplus fish feed outlet, comprising a circular duct, with grating on top, recessed in the inner bottom wall and with downward inclination to a lowermost elevation, where one valve, such as a remotely controlled butterfly valve, is arranged for faeces-surplus fish feed unloading. The outlet is coupled to a pump or similar, and connected piping directing the faeces, surplus feed, bilge in general, to a water separation system on the collar, to a compartment or tank on the collar or elsewhere, for further use or processing. The circular inclined duct has a downward inclination angle following the circular flow of the water in the tank. For the northern hemisphere farming tanks this direction is oriented clock-wise, opposite for southern hemisphere farming tanks. At the lowermost elevation of the duct, an edge is preferably provided, accumulating the faeces-surplus fish feed above the valve, due to inclination and water flow.

Unloading of farmed fish takes place in a recessed bilge well arranged in the upper double bottom wall, comprising a pipe penetrating the bottom plating in the bilge well, the pipe has diameter feasible for unloading of fish and further comprising a valve arranged for opening or closing the inlet to the pipe, the valve is preferably remotely controlled. Unloading of fish takes place with no other means than by help of gravity due to the constant maintained overpressure in the tank, in addition to optional underpressure in an unloading line coupled to a vessel. Any dead fish removal will be handled via the fish unloading piping system described above, preferably using compressed air as drive medium. The shape of the bilge ensures that the dead fish is captured and collected in the bilge well and can be sucked from the tank via the fish unloading system preferably using compressed air as driving medium.

The recessed bilge well further comprises an edge which will collect dead fish due to water circulation in the tank and secure that dead fish is lead to the suction point in the lowermost elevation of the bilge well. The recessed bilge well preferably comprises an inclined bottom on the side water flows in and the edge, sharp angled or vertical, on the opposite side. Compressed air will be used as driving medium to suck dead fish through the same outlet as for live fish unloading described above.

The outlet for faeces and surplus fish feed, and/or the recessed bilge well for unloading dead fish or live fish, as described and illustrated herein, are inventions also feasible for other fish farm concepts, representing independent inventions provided in addition to the fish farm concept of present invention.

The fish farm preferably comprises cameras and/or windows from the pump room or the access duct in the cigar directed at the fish unloading piping system, the bilge outlet and other areas in the tank, for facilitating and documenting the operation.

The fish farm preferably comprises a sloped upper tank bottom wall, that is the top wall of the double bottom wall, with a downward slope of about 15° or more radially inwards.

The inner side of the tank, and preferably the outer side of the tank and the collar, are preferably coated by a silicon-based coating, without any contents of copper or other poisonous material that will leach into the water. Such coating has a very low friction, allowing any bilge to sink down to the lowermost part of the tank bottom, facing the outlets. Unlike copper-soaked net or cage-based fish farms, and traditionally anti-fouling coated structures, no poisonous material, as far as we know, will pollute the water with copper or other heavy metals or contaminants, including phthalates and other substances that may affect organic life, including humans, in negative ways. Sacrificial anodes and/or applied current may however be required for achieving a service life of 30 or 50 years, and/or the structure may need re-coating after for example 25 years of service.

The fish farm comprises a quadratic, hexagonal, polygonal, rectangular, elliptic or circular tank, as seen in cross section.

The fish farm preferably comprises a water inlet at water depth of minimum 20 meters, preferably 23 m or deeper, such as 25, 30, 35 or 40 m or deeper depth below the surface of the surrounding sea. At this depth the existence of lice has not been found thus ensuring a lice-free water quality. To extend the water intake to deeper depths the water inlet preferably comprises a hoist mechanism and flexible tubing for adjusting the seawater intake depth, or several inlets that can be coupled inline or decoupled, so as to provide a more stable water temperature inside the tank, promoting good fish health and fish growth, such as around 8-18°C, most preferably around 12° C in addition to avoiding salmon lice.

Preferably, the fish farm is comprising several tanks such as 4, 6, 8, 10, 16, 25 or more, one single collar, such as a single continuous collar structure, or two or more collars combined with rigid coupling or flexible coupling with or without damping, and preferably further comprising one tank for collecting faeces and/or surplus food, one tank for any dead fish, and one tank for cleaning or conditioning of solved pollution from the outlet water and any other service or collecting tanks normally required for the operation of the farm. The only possible pollution from the fish farm apparently is any faeces and/or waste food dissolved into the water phase. If cleaning the dissolved pollution out from the water becomes very difficult or expensive, the water outlet can be at depth of the thermocline, that is the depth below where photosynthesis reaches and below where surface water is mixed, whereby the composition of the outlet water with dissolved pollution more or less match the water quality of the thermocline water. The thermocline water is naturally very high in nutrition contents, due to lack of photosynthesis and consumption of nourishment. The thermocline can start at 30 - 40 m in inshore waters, but most likely about 80 m of depth or deeper is the required depth of such water outlet. Preferably, the fish farm concept comprises a coupling or other arrangement allowing such thermocline deep water outlet to be coupled to the water intake for using such thermocline deep water as seawater for the tank. Thus, the fish farm concept should be safe for any poisonous algae bloom. If a deep water thermocline outlet or cleaning of dissolved pollution in the outlet water is practically or economically impossible, arranging a pipe to a nearby wastewater-sewage cleaning plant with cleaning of all or at least some of the dissolved pollution can be implemented, as a preferable feasible alternative.

The collar preferably comprises tanks needed for duties for farming operations such as but no limited to water ballast tanks, bio-fuel tanks and fish feed tanks. The collar can further be arranged with all needed infrastructure for farming operations such as but not limited to; fish feed system, oxygen production and storage system, ozone production and storage, cranes and winches, control room, engine room, switchboard and converter room, battery room, compressor compartment and processing rooms etc.

The result of the fish farm concept of the invention may be continued and even expanded fish farming in inshore waters, using existing infrastructure and supply routes, while providing a sustainable fish farming industry. To a full or a large extent, the fish farm concept is built using recyclable materials having a value that later can be sold and the value can be taken into account for long term calculations on the economic feasibility of the fish farm concept. Brief description of drawings

The fish farm of the invention is illustrated by Figures, of which

Figure 1 illustrates an embodiment of a fish farm of the invention as viewed from an oblique position,

Figure 2 illustrates a longitudinal section of a fish farm embodiment of the invention.

Figure 3 illustrates a longitudinal section of a fish farm of the invention with the tank at an elevated position, in a transport-cleaning mode position.

Figure 4 a top view of an embodiment of a fish farm of the invention.

Figure 5 illustrates an embodiment of damping in a fish farm of the invention.

Figure 6 illustrates possible details related to positioning and damping.

Figure 7 illustrates a constriction for unloading of fish

Figures 8a and 8b illustrate in section and obliquely the outlet for fish and the outlet for faeces-surplus fish feed, respectively.

Figure 9 illustrates in further detail the outlet for faeces-surplus fish feed.

Figure 10 illustrates a fish farm according to the fish farm concept of the invention.

Detailed description of the invention

The figures mainly illustrate structure required to understand the features discussed specifically for each specific figure, for increased clarity. The figures are in principle in scale for a specific, typical embodiment. Other embodiments can have different relative size of structures or components.

Reference is first made to Figure 1 illustrating an embodiment of a fish farm concept 1 of the invention as viewed from an oblique position, and Figure 2 illustrating a longitudinal section of a fish farm embodiment of the invention. Figure 1 illustrates a fish farm of the invention as it may look in operation, while Figure 2 illustrates some essential internal structure. More specifically, a fish farm concept 1 , comprising a tank 2 and a collar 3 are illustrated, wherein the tank 2 is arranged inside the collar 3. The tank 2 comprises water impermeable side structure and a water impermeable bottom wall, such as steel plates formed and welded. The fish farm concept further comprises at least one water inlet 4 to the tank and one water outlet 5 from the tank. The tank further comprises a double bottom wall 6,7, with one or more compartments 8 between the double bottom walls and inside the side structure, wherein one or more of the compartments can be ballasted and de-ballasted by operating a connected pump 9 and piping 10. In the illustrated embodiment, also a “cigar” 32 and seawater pumps 33 are illustrated. In addition, an access channel 34 in the “cigar” 32, and a pump room 35 as one of said compartments, are illustrated.

When the fish farm concept is in a fish farming mode, the tank is arranged in a lower position inside the collar, as illustrated in Figure 2. When the fish farm is in a transport-cleaning mode, the tank is empty for water, preferably the compartments between the double bottom walls are also empty or partly empty, and the tank is arranged in a higher position inside the collar, as illustrated in Figure 3. The downward arrows in the seawater circulation ducts illustrate that said ducts are emptied for water when the elevation of the tank increases.

The collar 3 is a floating structure with buoyancy at least sufficient to stabilize the weight of the empty tank in the higher position, in the transport-cleaning mode position. In practice, the collar is a relatively large and buoyant structure compared to existing fish farm concepts that are without any such collar with buoyancy at least as defined above. In practice, the collar 3 preferably includes a lot of the required infrastructure for fish farming, as will be further described. In practice, the collar preferably also is able to carry the weight of the tank fully filled with water, with or without fish, and preferably with normal infrastructure, as described below, included in or on the collar in a relevant design weather state for the location.

Figure 4 illustrates the fish farm concept as viewed from above.

Figure 5 illustrates an embodiment of damping in a fish farm of the invention. More specifically, structure 11 for vertical damping and structure 12 for horizontal damping are illustrated. The vertical damping 11 , comprising elastomeric material and springs, is arranged between a flange 13 of the tank and a seat 14 on the collar. Elastomeric structure 12 for horizontal damping is arranged between the tank and the collar. The damping is providing a longer service life of the fish farm concept since mechanical stress and fatigue are dampened, improved fish health, and allows sizing up the structure to in principle any practical size and any practical location, since transient stress levels and harmonic waves and momentums can be controlled by increasing or reducing the quantity and/or elasticity and/or damping of the damping structure. Rougher conditions, longer service life and larger structure require more damping.

Figure 6 illustrates possible details related to positioning and damping. Rollers, 15, 16, 17, preferably with elastomeric material outer structure, facilitates elevating (also termed lifting or hoisting) -lowering of the tank. Preferably, the rollers, arranged in ducts 18 on the collar, are not in contact with the tank in a smooth elevating - or lowering operation during normal operation.

Figure 7 illustrates a constriction 19 for unloading of fish. The constriction comprises an outer ring 20, an inner ring 21 and a net 22 or grating in between the rings. In some embodiments of the fish farm concept and the constriction of the invention, the constriction is without an inner ring, meaning that the net covers the full cross-section area of the tank. Such embodiments are useful for tanks without “cigar”. Controlled lowering of the constriction towards the outlet for fish in the bottom of the tank, preferably combined with a fish unloading line with underpressure coupled to a fish transport vessel, provides a smooth fish unloading with very low stressing of the fish. Figures 8a, 8b and 9 illustrate the outlets in the bottom of the inner tank wall, the upper wall of the double tank bottom wall. Figures 8a and 8b illustrate in section and obliquely the outlet 24 for live or dead fish and the outlet 23 for faeces-surplus fish feed, respectively. Unloading of live or dead fish are different operations, conducted at different times, routing the fish to different locations, as obvious for the person skilled in the art. Figure 9 clearly illustrates how the outlet 23 for faeces-surplus fish feed comprises a duct 25 with circular inclination downward toward the actual outlet 23, where an edge 26 or wall, vertical or near vertical, stops rotation of faeces-surplus fish feed just above the actual outlet 23. Figure 8 illustrates in further detail the outlet 24 for fish, comprising a recessed bilge well 26 with inclined wall 27 towards the water flow direction and an edge 28 or wall, vertical or near vertical, in the opposite side, arranged in the upper double bottom wall, and a pipe 29 penetrating the bottom plating 30 in the bilge well, the pipe has diameter feasible for unloading of fish and further comprising a valve 31 arranged for opening or closing the inlet to the pipe. The bilge well preferably is painted in a dark color, such as black or dark brown or dark green, providing what looks like a natural hiding place for fish when unloading, reducing stress on the fish. The unloading of live fish, but also other unloading, can preferably be facilitated by de-ballasting and some elevating of the tank during or before the unloading operation, for increasing flow when the unloading valve is opened, since the pressure in the tank will increase relative to connected piping and vessels.

Figure 10 illustrates one embodiment of virtually endless embodiments of a scaled-up fish farm according to the fish farm concept of the invention, including 12 tanks. Scaling up may improve the economy of the fish farm concept embodiments of the invention, due to shared infrastructure and utilities and larger quantity of farmed fish compared to costs of various kinds.

Unlike other fish farm concepts, the fish farm concept of the invention is feasible for growing fish from the smolt stage until grown up fish. Different tanks can provide grown up fish at different times. The use of open net based intermediate growth cages can be eliminated. The sustainability can be achieved for the full fish growth life in the sea by the present invention.

Claims

1.

Fish farm concept (1 ), comprising a tank (2) and a collar, (3) wherein the tank is arranged inside the collar; the tank comprises water impermeable side structure and a water impermeable bottom wall; the fish farm concept further comprises at least one water inlet (4) to the tank and one water outlet (5) from the tank, c h a r a c t e r i s e d i n that the tank comprises a double bottom wall (6,7), with one or more compartments (8) between the double walled bottom and inside the side structure, wherein one or more of the compartments can be ballasted and deballasted by operating a connected pump (9) and piping (10), wherein the tank in a fish farming mode is arranged in a lower position inside the collar, and wherein the tank in a transport-cleaning mode is empty for water and is arranged in a higher position inside the collar, and wherein the collar is a floating structure with buoyancy at least sufficient to carry the weight of the full, partly full or empty tank in the higher position, in the transport-cleaning mode position, wherein the tank is capable to be emptied for water by natural gravitation, without pumping water from the tank, with all or some of the double bottom ballast compartments de-ballasted, and with the tank (2) empty for water and all compartments (8) in the double bottom empty or near empty for water, the tank, by natural effects of buoyancy and gravity, is capable to be moved into the transport-cleaning mode position.

2 .

Fish farm concept according to claim 1 , comprising damping structure (11 ,12), such as elastomeric based and/or spring and/or fiber-cloth based damping material or -structure, arranged between the tank and the collar, the damping structure reduces the stress level when the tank is arranged in a lower position, in the fish farming mode, and/or when the tank is arranged in a higher position, in the transport-cleaning mode.

3.

Fish farm concept according to claim 1 or 2, wherein the tank comprises a flange (13) and the collar comprises a seat (14), wherein damping material or - structure, such as elastomeric based and/or spring based and/or fiber-cloth based damping material or -structure, is arranged between the flange and the seat, damping transient movements and wave movements, thereby reducing the structural and mechanical stress levels and the stress level of fish in the tank.

4.

Fish farm concept according to any one of claim 1 - 3, comprising a pump room (35) with one or more pumps (33) as one of the compartments between the double bottom walls, wherein seawater being pumped up to the tank is directed from one or more seawater pumps located in the pump room and/or in one or more vertical ducts welded to the outside of the tank and/or in a recessed room or -area in the collar.

5.

Fish farm concept according to any one of claim 1 - 4, wherein the tank comprises a central vertical structure, termed a cigar (32), which cigar is a combined water outlet from the tank and an access channel (34) from above sea level to the pump room, wherein a vertical water outlet section is perforated from a suitable elevation above the double bottom wall and up to the water surface in the tank as filled almost fully with water in a farming position, and a vertical access section of the cigar is a dry and safe access channel for personnel down to the pump room.

6.

Fish farm concept according to any one of claim 1-5, wherein the tank has negative buoyancy in the farming mode position, with a water level inside the tank higher than the water level of the surrounding sea, thus creating an overpressure inside the tank whereby water flows out from the tank without pumping, through a cigar of claim 5 or through another outlet.

7.

Fish farm concept according to any one of claim 1-6, further comprising a water penetrable constriction structure (19) that is capable to be arranged from top of the tank in downward direction until the tank has been emptied for fish, wherein the constriction structure comprises two ring structures, one outer ring (20) just smaller than the inner diameter or dimension of the tank and one inner ring (21 ) or structure just larger than the cigar structure, with a net or grate structure in between the ring structures, wherein the tank comprises an outlet for fish (24), towards which outlet fish is directed by the constriction structure.

8.

Fish farm concept according to any one of claim 1-7, further comprising a faeces-surplus fish feed outlet (23), comprising a circular duct (25), with grating on top, recessed in the inner bottom wall and with downward inclination to a lowermost elevation, where one valve, such as a remotely controlled butterfly valve, is arranged for faeces-surplus fish feed unloading.

9.

Fish farm concept according to any one of claim 1-8, comprising a recessed bilge well (26) arranged in the upper double bottom wall, comprising a pipe (29) penetrating the bottom plating in the bilge well, the pipe has diameter feasible for unloading of fish and further comprising a valve (31) arranged for opening or closing the inlet to the pipe.

10.

Fish farm concept according to any one of claim 1-9, further comprising a sloped upper tank bottom wall, that is the top wall of the double bottom wall, with a downward slope of about 15° or more radially inwards.

11.

Fish farm concept according to any one of claim 1-10, comprising a quadratic, hexagonal, polygonal, rectangular, elliptic or circular tank, as seen in cross section.

12.

Fish farm concept according to any one of claim 1-11 , further comprising a water inlet at depth of 23 m or deeper, such as 25, 30, 35 or 40 m or deeper depth below the surface of the surrounding sea, ensuring a water quality without sea lice and preferably without poisonous algae.

13.

Fish farm concept according to any one of claim 1-12, wherein the fish farm concept is a fish farm comprising several tanks such as 4, 6, 8 or 10 or more, one single collar, such as a single continuous collar structure, or two or more collars combined with rigid coupling or flexible coupling with or without damping, and further comprising one or more tanks for collecting faeces and/or surplus food, one or more tank for any dead fish, and preferably one or more tank for cleaning or conditioning of solved pollution from the outlet water.