Fish cage arrangement comprising a spherical fish cage

Abstract

A closed spherical net cage arrangement (10) suitable for farming fish in a position floating in water, comprising a polygonal pattern divided along a border line consisting of tubular elements (11) which together form a spherical frame, a plurality of window panes (13) covered by at least one layer of encircling net (51, 52), mesh, etc., said tubular members (11) containing at least one inflatable buoyancy member (60) in fluid communication with a reservoir of pressurized gas, a control unit (33) arranged to regulate the amount of gas in the buoyancy element, the tubular elements (11) are connected at nodes (12) by sleeves (42) and finger-like supports (40), and the tubular elements are arranged to allow water to flow into the parts of the tubular elements (11) not occupied by the buoyancy elements (60).

Description

TECHNICAL FIELD

[0001] The present invention relates to a cage arrangement comprising a closed spherical net cage for fish farming as set out in the preamble of claim 1. BACKGROUND

[0002] Industrial fish farming has for a long time been a major "industry" in many countries and the size and number of fish farms have increased substantially. The vast majority of the cages used commercially are open net cages in the sea and at its place the fish being reared are separated from the surrounding environment by a single layer of netting which hangs down in the sea like a large cylinder and is closed at the bottom but open at the top. The netting hangs from buoyancy elements which form a floating ring at the surface. This type of cage works well under ideal conditions, but in bad weather the cage is easily damaged and fish losses occur, and the protection against algae blooms, especially salmon lice, is minimal. Billions of Norwegian kroner are lost each year due to fish escaping, which also causes unnecessary stress to the wild fish population.

[0003] The existing installations also pollute the seabed and the surrounding area below the installation, since the installation lacks an effective solution for collecting waste from feed and excretions.

[0004] Due to the mentioned drawbacks, many measures have been proposed to overcome these problems or drawbacks, such as moving the entire installation to shore or using a more closed and better protected installation against one or more of the mentioned drawbacks. None of the proposals have so far proven to be simple and cheap enough to really compete with the existing installations, although in fact these proposals show technically better advantages than the open net cages.

[0005] US patent No. 8,424,491 B2 discloses a closed essentially spherical net cage structure designed as a triangular rigid beam section based on plastic or metal beam elements. The beam elements can enclose a conduit or inflatable elements. The system is submersible so that the entire cage can be immersed in water if necessary. According to the patent, different sizes of cages can be constructed from the same basic components, for example by using 80 or even up to 720 composite triangular elements, but since these elements are essentially rigid, a very high precision is required to join the elements at the required angles of the size. Therefore, it can be desirable to design a system which is more flexible and allows assembly of the components without having to ensure such precision.

[0006] A spherical net cage is known from Norwegian Patent No. 332 518, which is based on a beam support structure assembled to form a polygon with a net in the form of removable panels. Fixed buoyancy elements as well as inflatable buoyancy elements will be included in a number of beams, while some beams can contain only fixed buoyancy elements, only inflatable buoyancy elements or none of the parts.

[0007] Among other techniques known in the art, reference is made to SE 450 866 and US 5,251,571 A. SUMMARY

[0008] The object of the present invention is to provide a net cage for farming fish, which is simple in construction, easy to adjust to different sizes, simple and safe to operate, has low running and maintenance costs and is able to withstand storms with minimal risk of damage.

[0009] A further object is to provide a net cage which has good security against escape and has an inherent ability to protect the fish against lice and algae in the event of an algae bloom, and which has a low degree of pollution of the environment.

[0010] A further object is to facilitate anchoring and to provide good opportunities for moving fish into and out of the net cage.

[0011] The above-mentioned objects are achieved by a net cage according to the invention as defined in claim 1.

[0012] Preferred embodiments of the invention are disclosed in the dependent claims.

[0013] The net cage arrangement means that the invention not only relates to the net cage itself, but also to the physical equipment and control units connected externally, which are used, inter alia, to adjust the position of the net cage in the sea.

[0014] "Closed" as used herein means that there is a roof and walls in the net cage, however, it is not to be interpreted that any part of the net cage is watertight or airtight, unless explicitly stated.

[0015] The invention provides a net cage which is unique in construction and solves the challenges mentioned, inter alia, it can be completely submerged under water, which is a great advantage in bad weather, or as one of the measures to reduce the nuisance caused by salmon lice.

[0016] The submersion function of the net cage makes it possible to install a coastal farming facility where traditional net cage systems would not be able to withstand the powerful forces of nature that occasionally expose the facility to strong winds and huge waves.

[0017] The underwater net cage according to the present invention also offers advantages in terms of feeding, since the upper water mass can be avoided in critical situations, for example in the case of dangerous algal blooms, infestations by sea lice or release of environmental toxins. Other critical situations can be, for example, oil spills caused by discharges from the oil industry or maritime accidents.

[0018] Furthermore, the system with adjustable buoyancy / ballast can be controlled so that the net cage can be rotated in the sea so that any part of the net cage can be positioned above water level whenever needed, for example when cleaning, maintenance or installation of new equipment, transport channels for fish, etc.

[0019] The present invention consists of a closed net cage construction which has many advantages compared to the traditional net cage constructions currently used. The closed shape has clear advantages over the solutions applied today, since the risk of escape of the fish being fed through the closed net cage is significantly reduced. According to a preferred embodiment, the net cage has a double net solution which, among other things, allows continuous monitoring of several operating parameters, including damage to the net and the risk of escape. The net is divided into panels / sections for each of the construction elements / panes of the net cage and is attached individually to the buoyancy elements. The fact that the net is divided into sections has significant advantages compared to traditional net cages with large and heavy nets. The advantage of smaller net sections is that this method offers more convenient assembly and maintenance for other heavy operations like today, due to weight, size and tool requirements. If desired, the solution with net sections offers the opportunity to have additional net layers or other film types if this is considered expedient.

[0020] The construction of the net cage has the possibility of having at least two layers of net (or net plus film), which means that a filtering function with fabric / film as outer layer can be installed, and the construction of the net cage has the possibility of controlling and monitoring the water mass between the outer net section and the inner net section.

[0021] Thus, it is also within the scope of the present invention that the net cage has an inner relatively fine-meshed net that prevents escape of the fish and an outer coarse-meshed net that prevents predatory fish from passing through the net cage.

[0022] The net cage construction enables movement by towing even when the net cage is full of fish. It turns out to be desirable for the industry to move net cages with fish from an operational and safety perspective.

[0023] The size adjustment of the net cage with respect to its diameter can be done by choosing tube elements with different lengths and / or by changing the geometry of the finger-like supports so that the curvature is generally smaller or larger at each node.

[0024] The net cage of the present invention is lighter, easier to dimension and allows the use of more than one layer of netting or other types of "membranes" as needed for the environment compared to the closed structure known from US patent No. 8,424,491 B2. While four or five intersecting rigid beam elements are provided at each node of the net cage according to US 8424 491, there are three intersecting tube elements in the present invention and these three tube elements are easily arranged into prefabricated finger-like supports via separate sleeves, which make the installation as simple as erecting a tent in principle. While the finished net cage of the present invention is soft, elastic and flexible, the frame of the net cage of US 8,424,491 B2 is rigid. It is not that one net cage is better than the other in all conditions and all situations, but they are different, with fundamentally different properties despite common features. BRIEF DESCRIPTION OF DRAWINGS

[0025] In the following, the present invention will be described in more detail in the form of some selected non-limiting embodiments with reference to the accompanying drawings.

[0026] Figure 1 is a schematic side view of a net cage according to the present invention.

[0027] Figure 2 is a schematic side view of a net cage according to the present invention during operation.

[0028] Figure 3 is a schematic side view of a net cage according to the present invention in a submerged state.

[0029] Figure 4 is a schematic side view of two net cages according to the present invention during execution of operation.

[0030] Figure 5 is a perspective view of a tube element or the like constituting an element of a net cage according to the present invention.

[0031] Figure 6A shows an embodiment of a finger-like support according to the present invention.

[0032] Figure 6B shows an alternative embodiment of a finger-like support according to the present invention.

[0033] Figure 6C shows an assembly of parts of a finger-like support, a sleeve and a tubular element according to the present invention.

[0034] Figures 7A to 7C shows the principle of buoyancy according to the present invention.

[0035] Figure 8 shows another feature of a net cage according to the present invention.

[0036] Figures 9A to 9F Another advantageous feature of the invention is shown in different positions.

[0037] Figures 10A to 10B An assembly of several net cages according to the invention is shown.

[0038] Figure 11 Details of a particular variant of the invention are shown. DETAILED DESCRIPTION

[0039] Figure 1 A closed spherical net cage 10 according to the invention is shown floating in deep sea with its top protruding above the water surface. The spherical shape is obtained by a number of tube elements 11 mounted together in nodes 12 which together with the tube elements 11 define polygonal panes 13. In the shown embodiment the polygon is a combination of pentagons and hexagons. At least one layer of net covers most of the panes.

[0040] The upper panes of the net cage are covered by a roof 14. The roof can be impermeable or perforated, but usually constitutes a rigid element as explained in connection with another figure. The lower panes are covered by a floor 15 which is provided with further details including fastening means 16 for mooring lines 17 and a hatch 18 for discharge of waste from the net cage. The hatch 18 is usually equipped with means for opening and closing by a control unit. A safety line 19 is also shown as a supplement to the mooring lines 17. A buoy 21 with flag, light or other marking is attached to the net cage to make it easily visible.

[0041] As explained below, a buoyancy element or elements are arranged to be connected in each tube element 11 which enables the net cage to be placed at high or low levels in the water.

[0042] Figure 2 A net cage is shown in a situation where a service vessel 22 has arrived and connected a discharge hose 23 to the hatch 18 for pumping out solid waste from the lower part of the net cage. Figure 1 In practice one end of the discharge hose 23 can usually be connected to the hatch 18 while the other end is attached to the upper part of the net cage so that the discharge hose can easily be connected to a pump on the vessel without the need to perform any connection under water. The discharge hose 23 can alternatively be connected to a collecting device, e.g. in the form of an impermeable bag / container on the sea floor for temporary collection and storage.

[0043] Figure 3The net cage according to the invention is shown in the situation where it is pulled completely under water by winch 31 and preferably by suitable adjustment of the buoyancy in at least some of the buoyancy elements. In the area A at the top of the net cage, there is arranged an air-tight fabric which ensures that an air pocket is present when the net cage is pulled down. In area A, for example, solar panels can be fitted to store / supply energy so that the net cage is at least partly energy self-sufficient.

[0044] At the bottom of the net cage, in area B, there is usually arranged an impermeable fabric to collect solid waste until it is discharged via hatch 18. In the submerged state, a special buoy 32, usually equipped with a battery, a communication unit and a central control unit 33, will be able to transmit information to and from the net cage and control certain parameters in relation to the net cage, as described below. For example, the control unit 33 can be programmed to automatically lower the net cage under water when the wind and / or wave height exceeds a certain level. This can be done by activating winch 31 and adjusting the buoyancy using the buoyancy elements described below. The control unit 33 is arranged to be able to adjust the length of the mooring line 17 so that the net cage can be placed at the water surface when needed and so that the net cage can be placed more than 10 meters below the water surface when needed.

[0045] The communication unit in the buoy 32 can provide current information about the condition of the net cage and the position of the net cage and allow the operator to override the automatic devices. The buoy 32 is shown connected to the net cage by a cable 34 for transmission of power, air and gas and optionally communication, while communication with the operator preferably takes place wirelessly. If necessary, the winch 31 can be operated manually, but is preferably controlled by the control unit 33, which can automatically implement various measures based on external parameters such as wind, waves, etc.

[0046] One or more of the communication unit, the control unit and the battery can also optionally be arranged on the top plate 14 in a water-tight manner.

[0047] Figure 4 It is schematically shown how the tubular net 44 can be connected to the respective window in two net cages according to the invention placed close to each other. This can be done to move fish from one net cage to another to remove and control the fish or for example to meet the need to carry out major maintenance operations. For this purpose, the other closed windows 13 of the purse seine must be at least partly loosened in the relevant cell to enable the fish to pass through, or preferably the other closed windows of the purse seine are devices for opening and closing controlled by the control unit.

[0048] Figure 5A section of a tube element 11 is shown, which on one side has an inner enclosure 51 fastened with fastening means 53, and on the other side has an outer enclosure 52 fastened with fastening means. Inside the tube, a cable gate 54 is shown, which can contain a number of tubes for supplying air / gas to the buoyancy elements and for power to lights, cameras, etc. and for transmission of control signals.

[0049] Figure 6A A three-fingered finger bracket 40 for forming a node between tubular members of a net cage according to the invention is shown. The finger bracket typically has a slight angular variation between each finger, such that if one imaginary plane is placed through the centres of two of the fingers, the third finger will lie outside this plane. This contributes to the curvature of the surface formed by assembling the net cage, such that a spherical surface can be obtained without bending the tube elements 11 between the finger brackets. Figure 6A The finger bracket 40 is shown from its concave side, i.e. the side which in the installed state will face the net cage. Each finger on the bracket is equipped with fastening means, such as an annular flange 41 which is suitable for locking an adapted sleeve.

[0050] Figure 6B A finger bracket 45 is shown, which internally corresponds to the finger bracket shown in Figure 6A but has a substantially spherical outer shape. It works in the same way as the finger bracket 40, but the attachment to the sleeve can be implemented in another way, such as with an external bayonet attachment or a thread.

[0051] Figure 6C A (partial) section through a tube element 11 is shown, which is connected to the finger bracket 40 by means of a sleeve 42. The sleeve 42 is fixedly attached to the finger bracket 40 by means of the flange 41, possibly secured with a tension band 43, while the tube element 11 can slide back and forth within the sleeve 42 depending on external influences on the net cage. The length of the sleeve is such that the tube element cannot slide completely out of the sleeve even under severe stress. The enclosure net itself, which covers the net cage in at least one layer, preferably two layers, contributes to limiting the freedom of movement of the tube element, such that it cannot slide completely out of the sleeve.

[0052] As mentioned above, the assembly can be carried out without the use of welding, bolts or threads / screws.

[0053] The buoyancy elements, which are normally present in the tube elements, are not shown in figure 6.

[0054] Figure 7A A (partial) side section of a tube element 11 between two finger brackets 40 is shown schematically, with empty buoyancy elements 60 in the tube. The tube element 11 is shown with circular perforations. The purpose of the perforations is that water flows into or out of the tube element 11, respectively, when the buoyancy elements are emptied and filled.Figure 7B The same section is shown, but with half-filled buoyancy elements 60. Figure 7A Figure 7C The same section is shown, but with full-filled buoyancy elements 60. Figure 7A Figure 7B

[0055] The control unit 33 can be programmed to fill or empty the buoyancy elements in each tube element 11 individually. Alternatively, the tube elements 11 can be divided into different zones, so that the buoyancy elements 60 in each individual zone are emptied and filled simultaneously, but independently of the emptying and filling of the buoyancy elements in the other zones. Both options enable certain parts of the net cage to be made lighter, while other parts of the net cage are made heavier, so that the entire net cage can be rotated in the water, in order to bring any part of the net cage to the surface, for example for maintenance, repair, cleaning or connection and disconnection of equipment.

[0056] Figures 7A to 7C Supply lines for filling the buoyancy elements with air or gas and emptying the buoyancy elements from air or gas are not shown. The supply lines are usually located inside the tubes and internally routed between the tubes via finger supports. If desired, the buoyancy elements can be grouped in different sections, so that all buoyancy elements in the same section are filled and emptied equally, or alternatively, each buoyancy element is individually pressure-regulated. This sectioning reduces the need for the number of supply lines. For example, all buoyancy elements near the window 13 adjacent to the top plate 14 of the net cage can form one section.

[0057] Figure 8 The same section is shown, but with full-filled buoyancy elements 60. Figures 1 to 3 A net cage similar to the one shown in Fig. 1, but slightly enlarged, and showing the stabilizing chain 80 between the top plate and the bottom plate, which helps to reduce deviations from the spherical shape of the net cage when the net cage is subjected to forces in the sea, for example water flows caused by wind and tidal currents. The design with the tubular elements 11 that are free to move in the sleeves 42 also helps to reduce deviations from the spherical shape. The chain 80 between the top and the bottom is preferably arranged with damping and / or elastic elements (not shown), preferably with cylinders prestressed by springs or pressure.

[0058] Figure 9A The same section is shown, but with full-filled buoyancy elements 60. Figure 8 ​​​An alternative to the variant shown is that the chain 80 is replaced from top to bottom by a substantially rigid tube 90, preferably having a damping function (not shown) at at least one end. A displacement member comprising ribs 91 is arranged around a portion of the tube 90, the ribs being slidably attached to the tube 90 via a top sleeve 92A and a bottom sleeve 92B slidable along the tube 90. Each rib 91 has an upper and a lower portion connected by a pivot joint 93.

[0059] Figure 9B It shows the relationship with Figure 9A The same situation applies, but in a position where at least one of the top and bottom sleeves moves in the direction of the other sleeve, such that each joint 93 presents an angle other than 180 degrees. Between the winches above and / or below the joint 93, there is an impermeable fabric or a fine mesh fabric. The effect of at least one sleeve moving in the direction of the other sleeve is much like unfolding an umbrella.

[0060] Figure 9C The same situation is shown, in which the lower sleeve 92B moves further in the direction of the upper sleeve 92A, and the angle of the joint 93 has been reduced to about 90 degrees, resulting in the "umbrella" being further deployed.

[0061] exist Figure 9D In the process, the movement is completed such that the upper sleeve 92A and the lower sleeve 92B are adjacent to each other, and the fabric or fine mesh between the columns forms an internal "top" in the cage, which covers most of the horizontal cross-section of the cage. If more complete coverage of the cross-section is required, the fabric near the joint 93 may be extended and possibly supported by a flexible plastic friction element (not shown) that bends upon contact with the fabric of the cage itself.

[0062] Figure 9E and Figure 9F This illustrates how a displacement device can displace fish in the direction of the bottom of the net cage by shifting sleeves 92A and 92B downwards, with the sleeves still adjacent to each other and the fabric between the mandrels forming a movable inner top member of the net cage, such that the volume below the top member is gradually reduced. Figures 9A to 9F A similar method, as shown, can deploy an "umbrella" at a low level within the net cage, causing the fish to move upwards within the cage. The vertical movement of the displacement mechanism can also be controlled based on the buoyancy of the net cage.

[0063] Figure 10AA group of four cages 10 according to the application is shown in a side view, connected in a tetrahedron with an upper cage 10, which constitutes the node of three lower cages 10 located at the same or approximately the same vertical level. The upper cage is connected to the three lower cages by means of passages 105, which can be opened and closed as required. There can be different purposes for using this structure. For example, the upper cage can be located at the water surface and used for controlling and handling the fish, while the lower cages are used for more permanent stays and are located below the nitrate zone. For example, the transport of fish between one of the lower cages and the upper cage can be carried out by using a displacement device as shown in Figures 9A to 9F Figure 10A Any passages between the three cages located at the vertical level of the fiddle are not shown, but passages between the cages at this level can of course also be included.

[0064] Figure 10B Another group comprising three cages 10 is shown in a top view, located at the same vertical level in a triangular shape, each of the cages being connected to the other two cages via passages 105, which can be opened and closed as required. As an alternative to displacing the fish, the fish can be moved from one cage to another by feeding only one of the two cages, the passage between the two cages remaining open.

[0065] Other groups of two or more cages are also possible, as the windows in each of the cages are replaced by "windows" connected to transport passages, which also have a closing curtain that remotely opens or closes the transport path between the connected cages.

[0066] Figure 11 A particular variant of a cage 10 is shown, which is suitable for use as an upper cage in a group of cages coupled in a tetrahedron as shown in Figure 10A The cage comprises a tube 90 between the top and the bottom as shown in Figures 9A to 9F and in addition a platform 110 on which a person 112 can work for maintenance, feeding, medication, etc.

[0067] The platform 110 is typically constructed as a disc, which partly or completely surrounds the tube 90 and can be raised and lowered along the tube as required. The platform 110 can optionally be freely moved up and down along the tube 90 and is provided with floating elements that ensure that it always floats at the water level present in the cage.

[0068] The use of a displacement device as shown in Figures 9A to 9F can also be combined with the embodiment shown in Figure 11 ​​

[0069] As to the feeding of fish in the net pens according to the present application, this can be achieved in a number of ways, but primarily through an automatically controlled feeding system of the type known per se. Each net pen can have a feed reservoir at its top, which is filled periodically by a service vessel and is water-tight, so that the feed remains dry until it is dispersed in the water via appropriate feed nozzles. Any known type of feed useful for net pens in submerged state can also be used.

[0070] For the feeding of fish within the net pen, a solution can also be used in which the feed is fed from the bottom platform of the net pen. This is particularly important when using feed that is lighter than water, so that the feed will float upwards in the water mass during feeding. As the feed absorbs water, the feed will sink to the bottom. In this way, the fish will have access to the feed for a longer period, thus improving the utilization of the feed.

[0071] In addition, the deployment of the net pen and its surroundings is arranged with automatic or remote control functions, so that personnel do not have to be located on the net pen during its normal operation. Thus, in terms of safety for the personnel on board, it does not need to be equipped with access passages, personal safety equipment, etc., which is also a simplification compared to more traditional net pens.

Claims

1. A closed-type spherical net cage apparatus adapted for culturing fish in a position floating in water, the closed-type spherical net cage apparatus comprising: A paneled pattern of polygons divided along boundary lines consisting of tube elements (11) that together form a spherical framework; A plurality of panes (13) covered by at least one layer of enclosures (51, 52), nettings or some membrane against the surroundings, the tube elements (11) contain at least one inflatable buoyancy element (60) with a fluid connection to a reservoir of pressurized gas, and a control unit (33) arranged to control the amount of gas in the inflatable buoyancy elements, characterized in that the tube elements (11) are connected at nodes (12) by sleeves (42) and finger supports (40), and in that the tube elements (11) are perforated (63) and arranged to let water into the parts of the tube elements (11) not occupied by the at least one inflatable buoyancy element (60).

2. A closed net cage arrangement according to claim 1, characterized in that The sleeves (42) are attached to the finger supports (40) and arranged to surround one end of a tube element but not be fixed to it.

3. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i s e d in that One pane (13) is covered by a rigid bottom plate (15) that includes attachment means for mooring the net cage (10) to the seabed.

4. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d in that One pane (13) is covered by a rigid top plate (14).

5. The closed net cage apparatus according to claim 3, wherein The mooring is performed with mooring lines (17) or wires attached via winches (31) to bottom attachments (35).

6. A closed net cage arrangement according to claim 5, c h a r a c t e r i z e d in that The winches (31) are connected to a control unit (33) arranged to adjust the length of the mooring lines (17) so that the entire net cage can be placed at the water surface or at a position submerged at a desired depth as needed.

7. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d in that The upper and lower panes of the net cage are connected by chains (80) or tubes (90) that have the function of stabilizing the shape of the net cage.

8. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d i n that A plurality of the panes (13) are covered by inner (51) and outer (52) enclosures, the diameter of the tube elements (11) determining the distance between the layers.

9. The closed net cage apparatus according to claim 6, wherein The control unit (33) is arranged to reduce the amount of gas in at least some of the inflatable buoyancy elements (60) when the winches (31) shorten the mooring lines (17).

10. A closed net cage arrangement according to claim 9, characterized in that The control unit (33) is also arranged to control the winches (31).

11. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d i n that The gas in the reservoir is selected from the group consisting of air, inert gas and any combination of these.

12. A closed net cage arrangement according to claim 1 or 2, characterized in that The inflatable buoyancy elements (60) arranged to receive a defined amount of gas are divided into zones that allow the control unit (33) to supply different amounts of gas to different zones, thus causing the net cage to rotate as well as move vertically if needed.

13. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d i n that The upper area (A) of the net cage is lined internally with a gas-tight fabric that ensures a gas pocket in the upper part of the net cage in situations where the entire net cage is pulled underwater.

14. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d i n that The lower area (B) of the net cage is covered by an impermeable fabric adapted to collect solid waste in the form of excrement, dead fish and uneaten feed, and in which a discharge hose (23) connected to a hatch (18) at the bottom is arranged to periodically empty the solid waste from the net cage into a tank at a vessel or on the seabed.

15. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d i n that Two or more of the cages (10) are connected to each other by passages (100, 105) which can be opened and closed as required.

16. A closed net cage arrangement according to claim 1 or 2, c h a r a c t e r i z e d i n that The cage (10) also comprises a platform (110) arranged to enable a person to perform a work task in the cage.

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