Patent Description:
Industrial fish farming has grown to be a huge global industry over the last decades. A vast majority of the fish farms use sea-based fish cages where the fish is separated from the environment by net walls arranged in the form of a standing cylinder in the sea, downwards from the sea surface.

A number of issues are encountered with these fish cages. One problem is the stress on the fish cages in rough winds and high waves, which oftentimes occur along the coastline. During storms, major damages may occur and fish may escape from the cages, which represents economical loss as well as an environmental strain on the local wild fish.

Another problem is the salmon lice and toxic algae that tends to attack the salmon in these fish cages where the fish density is very high. Multimillions of Euros are spent each year on measures to reduce this problem, ranging from medicines, water-flushing, laser guns, mechanical means. Still, the problem is not eliminated.

More recently, the problems of salmon lice, algae and rough weather have been attempted solved by arranging land-based fish farms, which however requires a huge supply of water and oxygen to establish a sound environment in these plants. Others attempt to solve the problem by arranging closed, rigid containers in the sea and also by allowing the containers to be periodically submerged during storms to avoid damage caused by winds and high waves.

Another challenge involved in fish farming is the transfer of live fish from one fish cage to another or from a fish cage to a vessel for its transportation to a fish treatment station or to a processing plant where the fish is slaughtered and subjected to further processing steps.

To crowd the fish for harvest is labour intensive and stressful for the fish. This process demands two workboats and people working on the upper outer part of the cage. Most of the work is done manually and include safety risk. The fish are crowded in the pens using sweep nets. The density of the fish is difficult to control and may inflict unnecessary stress on the fish during the harvest.

An example of prior art fish cages is found in <CIT> which discloses a closed fish pen comprising a central vertical tube around which a horizontal ring is arranged and a flexible net being outstretched around the horizontal ring, said net having a first net side axially displaceable around the vertical axis, thereby allowing the inner volume of the fish pen to be reduced to expel fish through opening(s) in the central, vertical tube.

Other examples of prior art are found in <CIT>, <CIT>, <CIT>, <CIT>and <CIT>.

Still there seems to be a need for better, highly reliable and less costly solutions to the challenges of fish farming, in particular with regard to the mentioned problems caused by salmon lice and rough weather.

It is thus an objective of the present invention to provide a fish cage (system) for sea-based farming of marine species, which alleviates or eliminates the mentioned problems in a cost-efficient manner while maintaining or improving the safety for the personnel involved and to avoid unnecessary stress on the fish in its operation.

The above objective is fulfilled by the submersible fish cage according to the present invention as defined by claim <NUM>.

Preferred embodiments of the invention are disclosed by the dependent claims.

The fish cage according to the present invention is arranged to be positioned at an elevation e.g. <NUM> meters below the sea surface where the influence of waves is insignificant even in strong winds and where there is no occurrence of salmon lice or similar parasites.

A pocket of air arranged at the top of the cage allows the fish to adjust the pressure in its swim bladder to maintain its well-being under the elevated pressure.

Feeding of the fish is conducted by a wet feeding system using water to pump the pellets from the feed platform to the cage.

The mid-part of the fish cage exhibits similarities with traditional fish cages in that its shape is generally cylindrical and constituted by net walls, typically of two layers, a comparatively fine meshed inner net wall to hold the fish inside and a comparatively strong outer net wall to prevent sharks and other predators from destroying and penetrating the cage.

Buoyancy elements may be integrated in or attached to the bottom unit as well as to the roof of the cage. When the fish cage is to be raised to the sea surface, e.g. for transferring of fish, a winch on the sea floor mooring line is operated to release more of the mooring line, allowing the buoyancy elements to raise the fish cage.

Removal of dead fish and droppings is supported by either an airlift system or a grinder located in centre of the bottom part of the cage.

A particularly sophisticated feature of the present invention is the manner with which the fish cage allows its inner volume to be reduced when fish is to be transferred therefrom, by lowering the upper arms towards the lower arms by the use of a winch or buoyancy arrangement, allowing the flexible net wall(s) to be folded several times in a controlled manner as part of the process. This is elaborated further in the description of the drawings below. A rigid centre column extending from the bottom unit ensures that the fish cage has a steady orientation in all phases of operation, including the net walls, whether stretched or folded.

Below, the present invention is described in further details in the form of exemplary, non-limiting embodiments illustrated by the enclosed drawings.

<FIG> is a side schematic view of the frame work of a fish cage <NUM> in accordance with the present invention, comprising a bottom unit <NUM>, a centre column <NUM> attached to the bottom unit <NUM>, a number of radially extending lower arms <NUM> arranged around the centre column <NUM> at or near the bottom unit <NUM> as well as radially extending upper arms <NUM> attached to a roof <NUM> slidably arranged around the centre column <NUM>. Also shown are chains <NUM> arranged between the bottom unit <NUM> and the roof <NUM> for the purpose of raising and lowering the roof <NUM> and thereby the upper arms <NUM>. In the embodiment shown by <FIG>, there are six upper and six lower arms, arranged to suspend between them at least one tube like net wall defining the space to be occupied by the marine species in question, in particular fish. Generally, the number of lower arms (<NUM>) is at least four, more preferably at least six, and the number of upper arms (<NUM>) is equal to the number of lower arms.

By schematic is meant that the figure does not necessarily show all features that will be included in an actual embodiment and that the mutual dimensions are not necessarily correct.

As part of the roof <NUM>, at least one air pocket <NUM> may be defined by the side walls and top wall thereof, providing some buoyancy and a place for fish to adjust the pressure of their air bladder. Also, the bottom unit <NUM> may, and typically will contain at least one buoyancy chamber <NUM> for providing buoyancy to the structure as a whole.

<FIG> is a side schematic view of the frame work of <FIG>, showing a horizontal line <NUM> being attached to the outermost end of each lower arm <NUM>, thereby constituting a horizontal, polygonal shape at the lower end of the cage, defining the outer boundary of the "floor" of the fish cage. With the shown structure of six upper and six lower arms, each arm is angularly separated by <NUM> degrees from its adjacent arms and the polygonal shape of the line <NUM> is a hexagonal one.

As also shown in <FIG>, the positioning of the upper arms <NUM> as compared to the lower arms <NUM> deviates by <NUM> degrees so that each upper arm is positioned centred between two lower arms and vice versa. From a point close to the outermost end of each upper arm, a vertical line <NUM> extends mainly vertically down to an attachment point on the line <NUM> in between two lower arms <NUM> and more precisely at or near the mid-point between the two lower arms in question.

To each of the lines <NUM>, a number of battens <NUM> are slidingly attached. The battens <NUM> extends in opposite direction with a mainly horizontal orientation and are arranged to have one end attached to an inner net wall and the other end attached to an outer net wall. The battens <NUM> are rigid and will not fold or bend to any substantial degree and serve to hold the inner and the outer net walls separated at all times. The battens may be provided with buoyancy elements or weight elements, the significance of which to be explained below.

<FIG> also shows a hose <NUM> for transferring live fish to a vessel or the like at the sea surface. It furthermore shows a winch <NUM> located at the bottom unit <NUM>, connected to a mooring line <NUM> between the bottom unit and a base <NUM> on the sea floor. Although shown only in <FIG>, the hose <NUM>, the winch <NUM>, and the mooring line <NUM> will typically be present in connection with the different variants and embodiments of the present invention.

<FIG> shows the framework from <FIG> with an element of an outer net wall, attached thereto. This is for illustrational purpose only, since the separate elements of the net walls will not be separated in practice. The net wall element shown is a line <NUM> which is attached to every lower and every upper arm in a criss-cross pattern, providing a tight and straight line when the roof of the fish cage is in its uppermost position.

<FIG> shows the fish cage from <FIG> with an additional element of the net wall illustrated, namely a plurality of horizontal lines <NUM> around the periphery of the fish cage, each of which for being attached to one end of one the battens <NUM> shown in <FIG>. It should be mentioned that the horizontal lines shown does not give an indication of the mesh size of the net wall. There may be a plurality of meshes in between each of the shown horizontal lines.

<FIG> is an enlargement showing a top arm <NUM>, two bottom arms <NUM>, the criss-cross type line <NUM> of the net wall, the plurality of horizontal lines <NUM> of the net wall, as well as the lines <NUM> (<FIG>) on which the battens <NUM> are slidably arranged. As best shown by the further enlargement to the right, one end of the batten <NUM> is attached to the horizontal line <NUM> while the other end is free, but intended to be attached to a horizontal line of an inner net wall. It should be noted that the battens <NUM> may be attached to the net wall in different ways, hereunder in a juncture between a horizontal line and a vertical line.

Generally speaking, the inner and the outer net walls are separated by battens <NUM> slidingly arranged on lines <NUM> extending between the upper <NUM> and lower arms <NUM>. In practice, the lines <NUM> may be attached directly to the upper <NUM> and lower arms <NUM> or via lines, such as illustrated line <NUM> extending between the lower arms <NUM>. In a similar manner to line <NUM> a line (not shown) may, as an alternative, be arranged at the upper arms <NUM> for the line <NUM> to be attached thereto.

<FIG> is rather similar to <FIG>, the difference being that <FIG> shows a line <NUM> being an element of an inner net wall. The line <NUM> is arranged in a criss-cross pattern between lower <NUM> and upper arms <NUM> and are attached to the arms <NUM>, <NUM> a distance from their outer ends corresponding to the horizontal extension of the battens <NUM>.

In a similar manner, <FIG> is an illustration of horizontal lines <NUM> of the inner net wall similarly to the horizontal lines of the outer net wall illustrated in <FIG>. Each of these horizontal lines is arranged to be attached to one end of one the battens <NUM> shown in <FIG>, to thereby connect the inner and the outer net wall via these battens and at the same time ensure that the outer and inner net wall will not entangle with one another.

<FIG> is a schematic side sectional view of an outer net wall <NUM>, an inner net wall <NUM>, a vertical line <NUM> serving as a guide for sliding battens <NUM>, one end of which being attached to the outer net wall <NUM> and the other end attached to the inner net wall <NUM> in order avoid the outer and the inner net wall from being entangled with one another, in particular when the net walls are folded. As shown in <FIG>, the net walls are all stretched, corresponding to a situation in which the upper arms <NUM> are in their top position.

<FIG> shows principally the same as <FIG> but in a situation in which the upper arms (not shown) is lowered to some extent, thereby causing the outer <NUM> and inner net wall <NUM> to form loops <NUM>' and <NUM>' while the battens <NUM> are gathered on top of one another. The battens <NUM> and/ or the net walls <NUM>, <NUM> may have a density higher than the density of water, causing the lower part of the net walls to fold first, as shown. It is an option to use battens with a density lower than the density of water, which may cause the upper part of the net walls to fold first, assuming that the net walls as such do not have a density high enough to counteract the effect of the lightweight battens. In embodiments in which the battens have a density making them function as weight elements, additional weight elements may be attached to the net wall along the horizontal lines along the wall periphery at which the battens are attached to thereby increase the overall density at those lines, thereby improving the folding effect of the net wall. Similarly, in embodiments in which the battens have a low density making them function as buoyancy elements, additional buoyancy elements may be attached to the net wall along the horizontal lines along the wall periphery at which the battens are attached, also to improve the folding effect of the net wall.

<FIG> shows a situation in which the folding has been complete, at least for the part of the net wall shown in this Figure. Naturally, the lowering of the upper arms and the folding of significant parts of the net walls, reduces the space available for the fish, which is a common means in connection to transfer of fish out of a fish cage.

<FIG> shows an arrangement with a plurality of fish cages <NUM> according to the present invention connected to a common supply <NUM> of power and feed, the latter optionally being a barge, SPAR buoy or other floating or submerged device.

With regard to dimensions, these may be varied within wide limits according to need. Typically, the diameter of the fish cage is in the range of from <NUM> metres to <NUM> meters while the height of the fish cage in the range of from <NUM> to <NUM> meters.

The overall volume of the buoyancy elements of the bottom unit is typically in the range of from <NUM> to <NUM><NUM> while the overall volume of the buoyancy elements of the roof is in the range of from <NUM> to <NUM><NUM>.

The air pocket (<NUM>) at the top section is dimensioned in dependency upon the volume of the fish cage, its intended depth position in the water, and the duration for the intended use at such depth.

Claim 1:
Submersible fish cage (<NUM>) for sea-based farming of marine species, comprising a bottom unit (<NUM>), a centre column (<NUM>) attached to the bottom unit (<NUM>), a plurality of lower arms (<NUM>) radially oriented in relation to the centre column and evenly distributed around the centre column (<NUM>), directly or indirectly attached to the centre column, a plurality of upper arms (<NUM>) radially oriented in relation to the centre column and evenly distributed around the centre column, and at least one net wall (<NUM>) attached to the upper (<NUM>) and lower arms (<NUM>) in a manner defining a closed space for marine species, the upper arms (<NUM>) being attached to the centre column (<NUM>) via a roof (<NUM>) arranged around the centre column with means allowing vertical adjustment of the roof (<NUM>) in relation to the bottom unit (<NUM>), to thereby allow the volume defined by the net wall to be similarly adjusted, an outer net wall (<NUM>) and an inner net wall (<NUM>) being suspended between the upper arms (<NUM>) and the lower arms (<NUM>), characterized in that the outer net wall (<NUM>) and the inner net wall (<NUM>) are separated by battens (<NUM>) slidingly arranged on lines (<NUM>) extending between the upper (<NUM>) and lower arms (<NUM>).