The present invention relates to a fish farm and a method for supplying air and circulation of water in a fish farm, said fish farm comprises a float collar with a net, where the net is closed at the upper area by a lice skirt that extends partially down along the net. Furthermore, the fish farm comprises an air supply apparatus arranged to supply compressed air at a lower part of the net, whereby an ascending flow of water, made up of air bubbles and water in the net and water that is sucked into the net from the surrounding sea, where the water is sucked into the net from the surrounding sea in an area for through flow below the lice skirt.

Background of the Invention

There are several challenges in the fish farming industry, among these are lice, escapes, discharges into the environment, sludge, copper, mortality, use of areas, HS and operating cost, to mention some of them.

Furthermore, in stagnant fjords the lack of circulation can lead to oxygen-depleted water in the fish farm. Sludge from faecal matter and feed residues collect underneath the installation and one is now required to move these.

The occurrence of lice is a continuous challenge, particularly at the higher water levels. Lice thrive best in the upper water levels and the number of lice decreases at greater depths of water.

Disclosure of the state of art

JP H03154698 A shows that it is known to form an ascending flow of water by supplying a gas containing oxygen to a lower part of a fish farm. The water will be supplied oxygen and one gets a circulation in the fish farm.

US 4798168 A refers to a closed fish farm where it is known to take the surplus water out through the upper part of the closed fish farm.

From NO 340270 B1 a method and device are known for changing the upper water layer in fish farms supplied with means to prevent lice infected water getting into the net case, for example fish farms with lice skirts. The method comprises removal of water from the upper layers of water with the help of at least one appliance fitted with a water-expelling device set up in the fish farm and where the water that is removed is replaced by fresh water that penetrates into the fish farm through, or from, the underside of the lice skirt.

Objects of the present invention

With this invention a semi-closed fish farm is provided, with an air system integrated in the bottom of the fish farm that generates a stream flowing upwards. The fish farm can have a closed side and bottom but has a large opening on a lower side that sucks in water below the typical lice belt.

In an upper part, the fish farm can have an adjustable thin slit that lets in water and which can be closed completely on the side facing currents and wind. The whole of, or parts of, the slit can be closed automatically in accordance with the prevailing wind and current conditions. The pipe effect which is formed ensures efficient generation of a vertical flow upwards, which sucks in fresh water at the bottom and lets out water at the upper part of the fish farm.

It is an object of the invention to provide a fish farm and a method for supply of air and circulation of water in a semi-closed fish farm and that prevents the lice from entering the fish farm.

In this way, new areas for farming that have not been suited to today's solutions can be found.

The main reason for suppling air is to generate circulation with a secondary effect that some oxygen from the air dissolves in the water. According to the invention, it is also possible to supply extra oxygen to the air or use pure oxygen. Summary of the Invention

A preferred embodiment of the method according to the invention is given in the independent method claim, while alternative embodiments are given in the associated dependent claims. According to the invention, a method is provided for supply of oxygen and circulation of water in a fish farm, said fish farm comprises a float collar with a net, where the net is closed in an upper area by a lice skirt that stretches partially down along the net, where the method comprises the steps: supply of compressed air at the lower part of the net; formation of an ascending water flow of air bubbles and water in the net and water that is sucked in into the net from surrounding sea; where the water is sucked into the net from the surrounding sea in a flow through area below the lice skirt. Furthermore, the method comprises that the supply of compressed air to the lower part of the net is made in an area adjacent the bottom ring and remote from the centre of the net, and also involves discharge of water to the surrounding sea in an area above the lice skirt where the water is let out to the surrounding sea through a slit between the lice skirt and the float collar.

The slit can stretch around the fish farm and under the float collar, where the part of the slit that faces the prevailing wind and current conditions is closed.

To close the part of the slit that faces the prevailing wind and current conditions, a slit skirt can be raised or lowered.

Alternatively, to close the part of the slit that faces the prevailing wind and current conditions, a slit skirt can be displaced horizontally. Alternatively, the water can be discharged into the surrounding sea through one or more outlet pipes arranged under or in the float collar. Said outlet pipes can be opened or closed depending on the prevailing wind and current conditions.

The supply of compressed air at the lower part of the net can be provided with the help of an air supply apparatus in the form of one or more perforated pipes, hoses or mats that are connected to an air compressor, so that ascending air bubbles are generated.

The air supply apparatus can be placed at a distance from the centre of the net.

The air supply apparatus can be placed near the wall of the net.

Furthermore, the air supply apparatus can be placed near a bottom ring fastened to a lower part of the net.

The net is preferably closed at the bottom. The flow of water in a fish farm can be regulated by altering the air supply and/or the slit opening in the upper part of the fish farm.

In a further embodiment the height of an opening area of the region of the net below the lice skirt through which water can flow, can be regulated, whereby the water depth for the sucking of water into the net from the surrounding sea can be selected.

A preferred embodiment of the fish farm according to the invention is given in the independent product claim, while alternative embodiments are given in the associated dependent claims.

According to the invention a fish farm is also provided, comprising a float collar with a net that, at the bottom end, is fastened to a bottom ring and where the net in the lower area is closed by a funnel-shaped part, and that the net in an upper area is closed by a lice skirt that extends partially down along the net. Furthermore, the fish farm comprises an air supply apparatus placed in an area adjacent the bottom ring and remote from the centre of the net, where the air supply apparatus is set up to supply compressed air in a lower part of the net, whereby an ascending flow of water of air bubbles and water from the net and water that is sucked into the net from the surrounding sea, where the water is sucked into the net from the surrounding sea in a flow through area below the lice skirt, and also one or more openings for discharge of water to the surrounding sea in an area above the lice skirt.

The air supply apparatus can be one or more perforated pipes, tubes or mats, connected to an air compressor for the formation of ascending air bubbles.

The part of the slit that faces the prevailing wind and current conditions can be closable by raising or lowering a slit skirt with respect to the fish farm.

Alternatively, the part of the slit that faces the prevailing wind and current conditions can be closable by displacing a slit skirt horizontally about the fish farm.

Furthermore, the fish farm can comprise a water flow sensor and a wind sensor set up for automatic regulation of the slit skirt. The fish farm can also comprise a number of sensors in the form of temperature sensors at the outside and/or the inside of the fish farm, said sensors are set up to regulate the pumping of water into the fish farm. Description of the figures

Preferred embodiments shall be described in more detail in the following with reference to the enclosed figures, in which:

Figure 1 shows a section of a fish farm according to the invention, seen from the inside of the fish farm.

Figures 2 and 3 show a fish farm according to the invention, in an open and partially open position, respectively.

Description of preferred embodiments of the invention

The present invention provides a fish farm where air is introduced at the bottom and which generates an ascending flow of water. The water is let in at the side under the typical lice skirt, possibly in the bottom if the permanent bottom is not included and the water is discharged at the top. The lice skirt generates a pipe effect that activates the flow of water and prevents the lice from entering at the top and side.

Figure 1 shows a basically traditional fish farm 10 with a float collar 12, where a net 14 is suspended for the farming of preferably fish. A lice skirt 16 is arranged about an upper part of the net 14 to prevent through-flow of water with water that can contain lice. The net 14 can be fitted at the lower part with a bottom ring 22 and a closed funnel shape 28 that has an outlet 24 for handling of waste.

Meant by lice skirt 16 is a skirt or cover that surrounds and closes an upper part of the net 14 to prevent through-flow of water, or where the lice skirt 16 constitutes a closed upper part of the net 14 to prevent through-flow of water.

The lice skirt 16 is placed so that the upper edge lies mainly in the same plane or in the vicinity of the water surface of the surrounding seawater and such that a slit 20 or opening is formed between the lice skirt 16 and the float collar 12. The net 14 is not covered between the bottom of the lice skirt 16 and the bottom ring 22 so that a flow thought area for water is provided.

In an area preferably below the area through which the water can flow between the lice skirt 16 and the bottom ring 22, is an air supply apparatus 18 in the form of one or more perforated pipes, hoses or mats arranged for the release of compressed air. The pipe or the hose can be ring-formed or comprise sections that are distributed around the bottom of the fish farm. The air supply apparatus 18 is not placed centrally in the net, but preferably in an area near or adjoining the bottom ring 22, i.e. also near the wall of the net 14. The air supply apparatus 18 is connected to an air compressor which can, for example supply compressed air at a pressure of 2-8 bar, dependent on the depth of water.

By supplying compressed air at the lower part of the net 14, with the help of the air supply apparatus 18, an ascending flow is set up of water and air bubbles 30 and water in the net 14 and water that is sucked into the net 14 from the surrounding sea. The air bubbles 30 will drag along the water along as it rises. The water will also be sucked into the net 14 from the surrounding sea in the flow through area below the lice skirt 16 and contribute to increased upward flow of water, as indicated by the arrows A in figure 1 , and the water is thereafter discharged into the surrounding sea in an area above the lice skirt 16, as indicated by the arrow B in figure 1. In this way a pipe effect is set up that gets the water to flow out of the fish farm 10.

The slit that is formed between the lower part of the lice skirt 16 and the lower, open part of the net 14 can, if necessary, be adjusted so that the depth at which the water shall be sucked into the net 14 can be chosen. The adjustment can be carried out in that the lower part of the lice skirt 16 or another cloth (not shown) is fastened to a rope that runs down into the sea from the float collar 12. With the help of a winch and said rope the lower part of the lice skirt 16 or the cloth can be pulled up or let down. If a separate cloth is used, this can be a total coverage cloth, or alternatively the cloth that can be raised and lowered can have a ring-formed groove or slit with an opening for water.

Because of the pressure in the fish farm 10, which is formed by the supplied compressed air and the ascending flow of water, the surface of the water in the fish farm will be sufficiently higher than the surrounding sea water so that the water in the fish farm will flow over and out through the slit 20.

The water flow can be regulated by altering the air supply and/or the slit 20 at the top of the fish farm. At the side of the fish farm 10 that faces the prevailing wind and current conditions, there can be a risk for water entering through the slit 20 from the surrounding sea. Therefore, the slit 20 can be closed against the prevailing wind and current conditions. This can be carried out by, for example, using a slit skirt 26 fitted to the float collar 12 and which can be raised and lowered. The slit skirt 26 can comprise several sections that can automatically be driven up or down so that the slit 20 is closed in a required area. Alternatively, it can be imagined that the slit skirt 26 is suspended from the float collar 12 and can be automatically displaced horizontally so that it covers parts of the slit 20 as required, i.e. preferably the part that faces the prevailing wind and current conditions. Regulation of the slit can be automatic, in that a water flow sensor and wind sensor control which side of the fish farm has an open slit.

Meant with a slit skirt is a cover or closure that can close the slit 20 as required. The slit skirt 26 can be a cloth, cloth strip or a stiff plate material, which is placed so that it lies on the outside, on the inside or on both sides of the lice skirt 16.

In an alternative embodiment (not shown) the lice skirt 16 can be placed so that the upper edge is fastened to the float collar 12. Below the lice skirt 16 and between the bottom ring 22, the net 14 is uncovered so that a region through which water can flow is formed. To discharge water from the upper part of the fish farm 10, a number of outlet pipes are placed in or underneath the float collar 12. If there are very stable wind and current conditions, it can be considered that only one outlet pipe can be used, but in practice it will be more appropriate with several outlet pipes placed mutually spaced apart around the fish farm, and which can be opened or closed with respect to the prevailing wind and current conditions. The function and method will otherwise be as described earlier.

Furthermore, the fish farm 10 can comprise means to regulate the water temperature in the fish farm. For example, sensors in the form of temperature sensors on the outside and/or the inside of the fish farm 10 can be used to regulate the pumping in of the water into the fish farm. In the summer, the surface water can be too warm, so cold water can be pumped from the depths. The regulation can be carried out by pumping in cooler water, and also by regulating the depth from which the water is pumped in. In winter, the surface water can be too cold, and warmer water can be pumped in from the depths. The regulation can be carried out by pumping in more warm water, but also by regulating the depth from which the water is pumped in. Such regulation provides better fish welfare and better growth conditions throughout the year in that the temperature is as optimal as possible.