NO342703B1

NO342703B1 - System and device for temperature adjustment in a closed sea farm cage or a submerged aquaculture tank

Info

Publication number: NO342703B1
Application number: NO20171134A
Authority: NO
Inventors: Arne Geirulv
Original assignee: Aquaculture & Env Consulting As
Priority date: 2017-07-07
Filing date: 2017-07-07
Publication date: 2018-07-09
Also published as: NO20171134A1

Abstract

The present invention relates to a device (1) for temperature adjustment of inflowing water to an at least partly submerged closed aquaculture cage (2). The device (1) is particular suitable for increasing the temperature in a sea based unit, where the inlet water has a lower temperature than the water surrounding the cage (2). The device (1) com prises a helical tube (20) circumferentially arranged around the outside of the cage (2), a water inlet (21, 23) to the tube (20), a water outlet (22) from the tube (20) into the cage (2) in the upper region of the cage (2), and a pump (30) for pumping the water through the tube (20).The present invention relates to a device (1) for temperature adjustment of inflowing water to an at least partially submerged closed aquaculture cage (2). The device (1) is particularly suitable for increasing the temperature in a sea based unit, where the inlet water has a lower temperature than the water surrounding the cage (2). The device (1) com prises a helical tube (20) circumferentially arranged around the outside of the cage (2), a water inlet (21, 23) to the tube (20), a water outlet (22) from the tube ( 20) into the cage (2) in the upper region of the cage (2), and a pump (30) for pumping the water through the tube (20).

Description

Field of the invention

The present invention relates to a device for temperature adjustment of inflowing water to an at least partly submerged closed aquaculture cage as well as to a system for farming of aquatic organisms, such as fish, comprising a closed at least partly submerged aquaculture cage. The invention also relates to a use of such as device or system and to a method for temperature adjustment of water in a closed at least partly in water submerged aquaculture cage.

Background of the invention

The annual production of salmonids in Norway was about 1.3 million tons in 2012, 99 % being Atlantic salmon and trout. The production of salmon is at present mainly based on cage aquaculture in the sea, where salmon are cultivated in large net pen units. Sea based fish farming systems, such as used in farming of salmonids, typically comprise cages made of a net to retain the fish to be farmed. Using nets around the cages, these systems are water permeable allowing a direct water exchange with the surrounding water volume. Thus, farmed organisms are supplied with new, oxygen rich water by water exchange through the nets based on natural currents, tides, and waves. Disadvantages of these open systems are that there is no control on the quality, temperature and potential contamination of the inflowing water. In the recent years, in particular due to increasing problems with parasites and other harmful organisms such as poisonous algal blooms, different types of closed sea-based cultivation units have been developed and tested. These closed systems are typically more or less water tight cultivation units, e.g. made of tarpaulin, concrete or the like, which are used instead of nets. Water is pumped into these containers to supply the fish with fresh water and oxygen. Particulate sunken waste, such as faeces and feed losses, are typically removed at the bottom of the closed cultivation unit together with the effluent water.

Thus, closed system aquaculture, such as closed fish cages, provides a controlled interface between the fish and the natural environment and is used to avoid fish escaping the farm and to prevent parasites, such as sea lice and other harmful planktonic organisms, amoebas or poisonous algae from entering the cages. In salmon aquaculture, the need for chemicals for delousing can be reduced or even eliminated when cultivating the fish in closed systems. Closed system aquaculture also allows for controlling waste effluent and reducing emission of contaminants, such as remnants from feed or excrement, being products that can be collected.

An alternative to sea based closed system are land based closed fish farms. However these are often considered more expensive as a result of energy consumption and land use, amongst others. Closed systems in the sea are challenging due to the dynamic loads such as waves and currents, the need for technical installations connected to the water supply and waste handling as well as the static loads from the construction and hydrostatic forces.

One particular challenge with closed containment systems in the sea is the water exchange. The oxygen requirements by the fish can be covered by supply of fresh sea water and/or by pumping oxygen and/or air into the water of the closed tank. In most cases, pumping water from the surroundings into the cage is a preferred choice from an economical point of view. The water flow through the cage is also used to remove solid and dissolved waste which must be cleaned out. This includes both small particulate waste from feed remains, feces, dead plankton in form of sludge, as well as larger biomass such as dead fish etc.

Many potentially harmful planktonic organisms such as the infectious stages of salmon lice and poisonous algae (HAB – harmful algal bloom) are typically found in the upper layers of the water, close to the surface. The infectious free living stages of salmon lice, being positive photo tactic, are typically found in the upper 5 to maximum 10 meters from the water surface. It is therefore an advantage if the water to be pumped into the cage is collected from deeper water layers where the water is substantially free of lice, HAB and other potentially harmful planktonic organisms. In particular during summer, this has the consequence that the water supplied from deeper water layers is colder than the water temperature in the closed cage and the water close to the water surface.

Instead of pumping up water from lower water depth, submersible net cages which are submerged to water levels which are free of salmon lice, can provide a solution to avoid lice. However, these cages can only be submerged for certain periods for physostome fish, or it must provide a funnel giving access to the surface, so that the fish can inflate the swim bladder.

US 4798168 describes an arrangement for fish farming comprising a formed enclosure submerged in water and having a pump and hose arrangement to suction water from a depth having a favorable water temperature and expel the water within the enclosure through an outlet being oriented tangential to the horizontal circular cross-section of the enclosure.

One aspect of taking in water from deeper layers into closed sea cages is that this water has a lower temperature, at least during summer. Since cold water is heavier than warm water, it will sink towards the bottom of the closed cage. Thus, the cage will become heavier and may need added buoyancy to carry the increased weight of the tank. Circulation inside the cage can therefore be an important issue to efficiently mix the added oxygen-rich water with the water in the enclosure.

Furthermore, lower temperatures of the inflowing water affect the metabolism of the fish. The growth of the fish, being an ectothermic organism, is dependent on the surrounding environmental temperature. Higher temperatures generally increase the fish’s metabolism and growth. Colder water transported up from the deeper water layers can negatively affect the growth rate of the fish to be farmed. On the other side, higher temperatures can critically affect the oxygen saturation of the water in particular during summer time. Adequate oxygen levels are important for the fish, and lack of oxygen can lead to reduced appetite and growth, stress and potentially death.

KR 20120034487 describes a water temperature regulating device for a land based water storage tank. The device uses a heat exchange pipe supplied with fluid from a heat exchange supply, such as geothermal or air heat pumps.

CN 105941201 describes a fish breeding system comprising a heat exchange system outside a pond or tank. The heat exchange system comprises a heat exchange tank, through which the heat exchange fluid is passed through.

Thus, there is a need for a system and method to control the temperature of the water in closed sea based farming systems, in particular for closed systems floating in the sea, such as salmon cages, where the water is pumped up from adepth with low water temperatures.

An objective of the present invention is to overcome the problems and disadvantages described above.

In more detail, it is an object of the invention to provide a solution for obtaining a closed cage fish farm with good conditions for growth and well being for the fish.

Further it is an object to maintain a favorable temperature for the fish in closed cages. Moreover, it is an object of the invention to provide an environment equal to or as close as possible to the natural environment of the fish excluding damaging elements such as parasites. Yet an object of the present invention is to provide an energy efficient solution to obtaining a favorable temperature for the fish in the enclosure, resulting in reduced operational and investment costs. It is also an object to eliminate the need for added buoyancy due to weight increase as a result of taking in colder water in the cage.

Summary of the invention

The objects of the invention are achieved by a device and a system for temperature adjustment for a closed aquaculture cage as well as a use and a method as defined by the independent claims.

Preferred alternatives, variants and embodiments are also defined by the dependent claims.

Thus, in a first aspect the present invention relates to a device for temperature adjustment of inflowing water to an at least partly submerged closed aquaculture cage. The device comprises

- a helical tube circumferentially arranged around at least a part of the outside of the cage,

- a water inlet to the tube,

- a water outlet from the tube into the cage, and

- a pump for pumping the water through the tube.

By circulating the water through the helical tube, a heat exchange with the surrounding water outside of the closed cage is achieved. Thereby, a temperature increase of the water in the tube can be obtained, such that water with an increased temperature can be fed into the closed cage. In particular if the main water supply to the closed cage is based on water which is pumped up from deeper water levels, the temperature of the inflowing water is correspondingly low. A lower temperature of the water can negatively affect the growth of the fish and it has an impact on the weight of the water. Thus, the helically arranged tube on the outside of the cage allows increasing the water temperature on its way from e.g. a lower region of the cage to an upper region of the cage, by heat exchange with the surrounding water. The pump can be any suitable pump such as an airlift pump.

In a preferred embodiment, the water inlet to the tube is connected to the cage in the lower region of the cage, preferably to the water outlet of the cage which is typically at the lowest portion in the center at the bottom of the cage. In this case, at least a part of the outflowing water from the cage will be recirculated in the helical tube and reintroduced into the enclosure. By removing water from the main outlet from the cage, existing technical structures from the cage can be used for the water removal and no separate water outlet is necessary. Cold water introduced into the cage at the top, will sink down to the bottom of the cage. By recirculating at least a part of this water, an increase in the overall water temperature can be obtained.

In another preferred embodiment, the water inlet to the tube is connected to a water supply pipe receiving water from the surrounding environment, preferably from an area which is substantially free of harmful planktonic organisms such as free living infectious stages of parasites, and/or microalgae. This is particularly relevant for farming of Atlantic salmon and the infectious, free living stages of the parasitic salmon lice, Lepeophtheirus salmonis. Said water supply pipe can be the main water supply for the cage. Preferably the water supply pipe receives water from a water depth of at least 20 meters from the water surface, more preferably from at least 50 meters. The water temperature, in particular when collected from deeper zones in the water column to avoid contaminations, is generally lower than in the upper layers, at least during summer. By circulating at least a part of this water around the cage, thereby achieving a heat exchange with the water surrounding the cage and having a higher water temperature, it is possible to increase the water temperature of the supply water.

The water outlet of the tube into the cage can be at the water surface or in close vicinity to the water surface.

It is particularly preferred that the tube has an inlet valve for intake of water from the cage and/or the water supply pipe. This has the advantage that it is possible to choose in operation whether the water from the main water supply or water from the cage will be fed into the helical tube for heat exchange.

The coil pitches of the helical tube can either be

- evenly distributed along the vertical height of the cage, or

- the coil pitches of the helical tube in the vertical direction are smaller closer to the water surface than closer to the bottom region of the cage, or

- the coils are only arranged in the upper part of the cage. The advantage of having a higher number of coil pitches close to the water surface or of only having coils there, is that the water temperature in this zone is often higher due to the sun warming up the water close to the surface. A better heat exchange will therefore be obtained in this zone than further down in the water column.

The helical tube can have a diameter between 50 and 200 mm, preferably between 90 and 180 mm. Using tubes with this diameter has the advantage that the volume to surface relation of the pipe is suitable for the heat exchange. Moreover, tubes of these dimensions, in particular if they have certain flexibility such that they can be bended, are easy to install and handle in operation. These pipes can be produced in continuous lengths of several hundred meters.

A second aspect of the present invention relates to a system for farming of aquatic organisms, such as fish, comprising a closed at least partly in water submerged aquaculture cage, whereby the system further comprises a device according to any of the preceding paragraphs.

Typical cages used according to the present invention are floating constructions, where an enclosure such as a bag, container or tank, is extending downwards from the water surface and where the enclosure comprising the farmed organisms is opened at the surface.

Preferably, said cage has a main water supply pipe transporting water into the cage from a water depth being substantially free of harmful planktonic organisms such as salmon lice. It is particular preferred that the water for the main water supply is from a water depth of 50 meters or more. By using water from this depth, one can avoid to introduce into the cage contaminations by parasites and other harmful planktonic organisms which are often distributed in the water close to the surface.

In a third aspect the present invention relates to a use of a system or device according to any of the preceding paragraphs, for raising the temperature in the cage. A particular preferred use is for achieving a temperature in the cage equal or close to the temperature in the surrounding environment. By increasing the temperature in the cage, the growth of fish can be increased. Furthermore the weight of the water will be lower, leading to a reduced weight load of the cage.

A preferred use is for farming of marine organisms, in particular aquaculture animals, such as fish. This comprises a species selected from fish and shellfish which can be cultivated in an aquaculture cage. Preferably, this can be a species selected from the group consisting of teleostean fishes, molluscs, crustceans, and echinoderms. Particular uses are for species selected from the salmonids, cod fishes, basses, breams, flatfishes, groupers, tilapia, most preferred Atlantic salmon, Salmo salar. A use in farming of Atlantic salmon to avoid transporting infectious, free living stages of the parasitic salmon lice, Lepeophtheirus salmonis, into the cage, is of high relevance.

Finally, the present invention relates in a further aspect to a method for temperature adjustment of water in a closed at least partly in water submerged aquaculture cage, whereby the cage is provided with a device as disclosed above. The method comprises

- pumping water through the helical tube into the cage whereby the inlet of the tube (i) receives water from the cage in the bottom region of the cage, and/or

(ii) receives water from a water supply pipe transporting water from the surrounding environment into the cage.

The water supply pipe can be the main water supply to the cage and whereby the main water supply transports water from water depths where the water is substantially free of harmful planktonic organisms such as salmon lice, preferably from a water depth of 20 meters or more, more preferably of 50 meters or more.

At least some of the water exiting from an outlet of the cage can be circulated through the tube outside the enclosure for heat exchange with the surrounding environment before reentering the closed cage.

Description of the diagrams

Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein:

Figure 1 shows schematically a side view with a partial cross section of a device and a closed aquaculture cage according to the invention.

Figure 2 shows schematically a perspective side view of a device and a closed aquaculture cage according to the invention.

Figure 3 shows schematically a perspective side view of another embodiment of the present invention, wherein the water to be transported through the helical tube of the device either derives from the outlet of the cage or from the main water supply pipe.

Figure 4 shows schematically a perspective side view of another embodiment of the present invention, wherein the water is first pumped to the surface and then introduced into the helical tube at the surface. The arrows indicate the principal water flow direction through the device.

Detailed description of preferred embodiments of the invention

The following description of the exemplary embodiment refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to various forms of devices for temperature adjustment and temperature increase for a sea-based fish farm. It should be appreciated, however, that the referenced device for temperature adjustment is also applicable and suitable for use in respect to other types of closed aquaculture systems, requiring temperature adjustment and being suitable for a heat exchange with the surrounding environment. Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment.

In the description relative terms such as front, top, center, bottom, side, downward, upward, sideward, vertical and horizontal etc. are all related to the device when in upright position i.e. when mounted to a farm cage floating or submerged in water. Correspondingly, lower and upper half of the cage refers to when the cage is suspended/submerged in its intended position in water. Even though only exemplified for one side, it is to be understood that some features will correspondently also apply for the opposite side of the device.

In the context of the present invention, a closed aquaculture cage refers to a cultivation unit or cage, most commonly a cage located in a body of water, typically a sea-based or lake-based fish farm cage. The term includes closed systems where the farmed organisms are kept in a more or less water tight container, tank, or bag, effectively stopping or at least significantly reducing a direct water exchange with /inflow of the surrounding water. The cage has an external water supply by one or more pumps. If only partly submerged (floating), the cage can be an open construction i.e. the top side of the cage facing to the water surface can be open. If totally submerged in the water, also the upper side of the cage is closed to retain the fish. The cage can typically be made of any suitable material such as concrete, a cloth, a tarpaulin material, other plastic materials, metal, glass fibers, composite materials, very fine meshed net materials stopping harmful planktonic species to enter the cage or combinations thereof.

Even though preferred, the use of a device according to the present application is not restricted to sea water, but may also include fresh water and brackish water aquaculture. It is to be understood that a cage according to the present invention further comprises conventional constructive elements for water submerged aquaculture cages well known to the skilled person without being described in detail such as mooring means, floating and ballasting means, means for waste handling, feeding, control of environmental parameters and the like. These are all means which are well known to the skilled person in the field and will only be described if they are relevant for the invention.

Although less preferred a closed aquaculture cage may even include landbased systems in cases where a heat exchange with the environment can be achieved by a device as disclosed according to the present invention.

By harmful planktonic organism according to the present invention is meant any harmful or potentially harmful organism for the farmed organism inside the aquaculture unit. The harmful organism has at least one planktonic free-living life stage such as certain parasitic organisms (e.g. salmon lice), harmful micro algal blooms (HAB), amoeba, etc.

By submerged is meant in the context of the present invention that the cage can be partly or totally submerged in water.

Figure 1 and 2 show schematically one embodiment of the invention. The figures show a closed cage 2 in form of a closed bag 10 suspended in a floating collar 11. The bag is submerged in water and is open at the water surface. At the bottom of the bag 10 is a cage outlet 12 where water from the bag 10 and collected waste such as sludge, can be removed. The bag is provided with a water supply 13 comprising a water supply pipe 14 with a water supply inlet 16 in an area below the cage 2 and a water supply outlet 18 at the upper side of the cage 2, typically at the water surface or in close vicinity to the water surface, for water inflow into the bag 10. The water supply 13 is provided with pumps (not shown). Typically the main water supply 13 for the cage 2 transports water from deeper water levels, which are substantially free of harmful planktonic organisms, up the cage 2.

In the shown embodiment, a circulation tube 20 is coiled on the outside around the bag 10 in a helical path. The tube 20 has a tube inlet 21 connected to the outlet 12 of cage 2 at the bottom of the bag 10 and has a tube outlet 22 for water into the cage at the top of the bag 10. A pump 30 for pumping the water through the tube 20 is placed above the water surface in close vicinity to the floating collar. The pump is pumping water from said tube inlet 21, connected to the cage outlet 12, through the helical tube 20, to the upper part of the bag 2, where the water reenters the bag 10 through the tube outlet 22. The tube outlet 22 is shown directed downwards; however, it could be positioned to supply the water into the enclosure in other directions, for example in order to create a favorable current or circulation inside the enclosure. The pump 30 is used to enable the water to run up through the tube 20, and hence, could be supported by more pumps or could for example be placed near the circulation tubing inlet 12.

In an alternative embodiment, the tube 20 may also receive water from a separate tube inlet in the lower half of the cage 2, preferably close to the bottom area of the cage, whereby it is not connected to the main outlet 12 of the cage (not shown).

The function of the helical circulation tube 20 is to create an enlarged surface for heat exchange with the surrounding environment. What is important for the invention to be effective is that the contact area towards the surrounding environment is large enough to obtain a favorable temperature increase or decrease in the water in the enclosure. For a floating fish farm cage, this ensures that the water inside the enclosure will exchange heat with the water outside the enclosure, and the enclosure will achieve a temperature more or less close to the surrounding water, and thus a favorable temperature for the fish/ farmed organism in the enclosure. This is particularly beneficial when collecting fresh sea water at deeper water layers, which often has a lower temperature than the water closer to the surface, and introducing it into the cage.

Figure 1 and 2 further show that the helical tube 20 is supported and fixed in their position by a number of vertical fastening means 40 on the outside of the cage 2 along the circumference of the cage. The fastening means typically comprise a line provided along their length with a number of fastening loops 41 for receiving the tube 20. The vertical fastening arrangement can e.g. be in form of a strap, a wire, a chain, a rigid bar or the like. Typically the line is fastened in the top part of the cage 2 e.g. to the floating collar 11. The line is typically provided with a ballasting weight 42 at the lower end to ensure that it is kept vertical or substantially vertical. Other types of fastening loops 41 can be arranged periodically along the vertical straps 40. The tube 20 is inserted in through the loops 41 when coiled around the enclosure, and this will ensure that the circulation tubing maintains its helical shape. For a bag of for example 24m in diameter and 10m depth, a circulation tubing of 150mm diameter could have 1,6m width between each turn in the helix. This would result in approximately 600m length of circulation tubing in the helix. The circulation tubing is preferably made of a flexible tubing material with a minimum bending radius suitable to coil around the enclosure (outside of bag 10). The material properties in the tubing, such as thermal conductivity and the SDR (standard dimension ratio) value can be optimized to achieve an efficient heat exchange while still having a durable and flexible tubing appropriate for use in seawater. A polyethylene (PE) tubing is an example of material suitable for this purpose. The helical tubing typically has a neutral or slightly positive buoyancy.

Instead of a flexible tube, which has the advantages that it is adjustable to different types and forms of cages on site, as described above, the tube can also be rigid and/or self supporting. A rigid tube could be used for e.g. closed cages made of glass fiber or concrete. In this case it is an advantage if the rigid tube is prefabricated and mounted to the cage during its production. The cage walls may also be provided with recesses to receive the tube 20 on its outside. Thereby additional fastening means may be omitted.

Instead of an even distribution of the helical coil pitches of tube 20 along the height of the cage 2, the pitches of the tube may have different extensions. In a preferred embodiment, the coil pitch distance is smaller in the upper half or region of the cage (closer to the surface) than in the lower half or region (closer to the bottom). This has the advantage that the heat increase can be higher since the water temperature, at least during summer, is often higher in the upper region of the water column closer to the water surface. A better heat exchange can be achieved by this uneven coil distribution. In an alternative embodiment (not shown), the tube 20 extends vertically a certain distance upwards before it is formed in helical shape further up in the water column.

In another embodiment as schematically shown in figure 3, the helical tube 20 can alternatively receive water directly from the main water supply 13. In the shown embodiment there is a valve 17 allowing to receive water either from the cage (recirculation) or from the main water supply 13. This is particularly interesting in the case where more (non-circulated) oxygen rich water shall be added to the cage. The helical tube 20 may also receive water from both the water supply 13 and the cage 2.

Alternatively to being connected to the main water supply pipe 14, the helical tube may 20 have its own water supply pipe (not shown).

In yet another embodiment, the cold water collected from a lower region of the cage e.g. at the tube inlet 21, is first pumped up to the upper/top region of the cage through a lifting tube 25, i.e. to the water surface (Figure 4). This can be done by an air lift pump (Mammoth pump) or the like. The lifted water is then introduced into the circulating helical tube 20 and will be transported through the tube 20 to a lower region/lower half of the cage. Thereby, an improved heat exchange can be achieved in particular if there is a high number of pitch coils of the tube 20 close to the surface where the water is warmest during summer. When the water reaches the lower region/lower half of the cage, where the water is colder, it can be pumped up again through a feeding tube 24 and reintroduced into the cage 2 in the upper/top region via the tube outlet 22.

Although only illustrated in figure 4 for the embodiment where water is taken out from the cage 2, it is to be understood that this principle arrangement will also be possible with water being supplied from a water supply pipe 14 i.e. water taken from the environment. Furthermore, an arrangement with both options and corresponding valves is possible i.e. an alternative supply of water from either the cage 2 and/or a water supply pipe 14.

The optimal amount of water to be recirculated through the helical tube 20 versus the water coming in from the main water supply 13 will depend on several parameters such as the biomass of fish in the cage, the density, the size of the fish, the water temperature, the oxygen consumption by the fish, the oxygen saturation of the water in the cage, the total water exchange etc. These parameters can be measured and monitored such that the operator can adjust the amount of water to be recirculated to the actual needs by suitable means for regulation and control of the water flow into the cage via the different tubes and pipes for water supply. It is also possible to add additional oxygen or air from an external source to the cage if needed.

Claims

1. A device (1) for temperature adjustment of inflowing water to an at least partly submerged closed aquaculture cage (2),

c h a r a c t e r i z e d i n t h a t the device (1) comprises

- a helical tube (20) circumferentially arranged around at least a part of the outside of the cage (2),

- a water inlet (21,23) to the tube (20),

- a water outlet (22) from the tube (20) into the cage (2) and

- a pump (30) for pumping the water through the tube (20).

2. A device (1) according to claim 1, wherein the water inlet (21) to the tube (20) is connected to the cage (2) in the lower region of the cage (2), preferably to a water outlet (12) in the bottom of the cage (2).

3. A device (1) according to claim 1, wherein the water inlet (23) to the tube (20) is connected to a water supply pipe (14) receiving water from the surrounding environment, preferably from an area which is substantially free of harmful planktonic organisms such as free-living infectious stages of parasites, and/or microalgae.

4. A device (1) according to claim 3, wherein the water supply pipe (14) is the main water supply for the cage (2).

5. A device according to claim 3 or 4, wherein the water supply pipe (14) receives water from a water depth of at least 20 meters from the water surface, more preferably from at least 50 meters.

6. A device according to any of the preceding claims, wherein the water outlet (22) of the tube (20) into the cage (2) is at the water surface or in close vicinity to the water surface.

7. A device (1) according to claim 2 or 3, wherein the tube (20) has an inlet valve (17) for intake of water from the cage (2) and/or the water supply pipe (14).

8. A device (1) according to any of the preceding claims, wherein coil pitches of the helical tube (20) are either

- evenly distributed along the vertical height of the cage (2), or

- the coil pitches of the helical tube (20) in the vertical direction are smaller closer to the water surface than closer to the bottom region of the cage (2), or

- coils are only arranged in the upper part of the cage (2).

9. A device (1) according to any of the preceding claims, wherein the helical tube (20) has a diameter between 50 and 200 mm, preferably between 90 and 180 mm.

10. A system for farming of aquatic organisms, such as fish, comprising a closed at least partly in water submerged aquaculture cage (2) characterized in that the system further comprises a device (1) according to any of the preceding claims.

11. A system according to claim 10, wherein the cage (2) has a main water supply pipe (14) transporting water into the cage (2) from a water depth where the water is substantially free of harmful planktonic organisms such as salmon lice, preferably from a water depth of 50 meters or more.

12. Use of a system or device according to any of the preceding claims, for raising the temperature in the cage (2), preferably achieving a temperature in the cage equal or close to the temperature in the surrounding environment.

13. Use according to claim 12, for farming of marine organisms, in particular aquaculture animals such as fish.

14. Method for temperature adjustment of water in a closed at least partly in water submerged aquaculture cage (2) c h a r a c t e r i z e d i n t h a t the cage (2) is provided with a device (1) according to claim 1 and the method comprises

- pumping water through the helical tube (20) into the cage (2) whereby the inlet of the tube (20)

(i) receives water from the cage (2) in the bottom region of the cage (2), and/or (ii) receives water from a water supply pipe (14) transporting water from the surrounding environment into the cage.

15. Method according to claim 14, wherein the water supply pipe (14) is the main water supply to the cage (2) and whereby the main water supply pipe (14) transports water from a water depths where the water is substantially free of harmful planktonic organisms such as salmon lice, preferably from a water depth of 20 meters or more, more preferably of 50 meters or more.

16. Method according to claim 14 or 15, wherein at least some of the water exiting from an outlet of the cage (2) is circulated through the tube (20) outside the enclosure, for heat exchange with the surrounding environment, before reentering the closed cage (2).