NO345372B1 - System for sorting of living fish - Google Patents

Description

SYSTEM FOR SORTING OF LIVING FISH

FIELD OF THE INVENTION

The present invention relates to a system for sorting of living fish while moving the fish from one place to another, for instance while loading fish from a fish cage to a fishing carrier, or while loading the fish from a boat to a processing plant or the similar on shore. The system may be used in any other situation where living fish are transported from one place to another, and where a gentle sorting is desirable. The system for sorting of living fish comprises an inflow section with an upstream end for receiving of fish, a gully and at least two receiving sections. The present invention also relates to a method and a use of the system for sorting of living fish of different length and characteristics in their surface structure, such as lumpsucker and salmon.

BACKGROUND

Infestations with sea lice including Lepeophtheirus salmonis and Caligus elongatus are currently considered to be one of the most important disease problems in farming of salmonids, especially in Atlantic salmon and rainbow trout. In addition to the costs that are associated with treatment, lower classification ratings of slaughtered fish and reduced growth rate due to reduced feed intake contribute to the economic losses caused by sea lice. Moreover, sea lice infections represent a serious problem for fish welfare and health as such.

Many delousing methods for treatment of lice infection of fish are considered environmentally hazardous. Moreover, extensive use of drugs and chemical methods for treatment of lice resulted in resistances of the lice against many commonly used agents. Besides chemical methods, different physical and mechanical methods are used to remove lice attached to the fish. The disadvantage of many of these methods is that they have negative effects on fish welfare and in many cases lead to an increased mortality.

In order to reduce the problems related to sea lice, it is a common practice that farmers add cleaner fish, such as species of wrasse or lumpsuckers, Cyclopterus lumpus, into the fish net cage for delousing of the salmon. The cleaner fish such as the lumpsuckers will eat the ectoparasitic sea lice from the fish’s skin, and thus clean the farmed fish and reduce the infection rates. The use of cleaner fish thereby offers an alternative to medicines for sea-lice control and is generally considered as an environmentally friendly method and not stressful to the fish.

Lumpsuckers compared to wrasse have the advantage that they also feed at low temperature during winter, while wrasse have a period of winter dormancy. Thus, the production and use of lumpsuckers for salmon farming has increased exponentially and lumpsucker is now the species, which is most commonly used in salmon production.

Lumpsuckers can reach a maximum of 40-50 cm in length, and their body shape is drop-like/ball-like. Lumpsuckers used as cleaner fish in salmon production are considerable smaller than the grown farmed fish such as the Atlantic salmon Salmo salar, but may have about the same thickness. Thus, the overall volume of a lumpsucker is much smaller due to their shorter length compared to a salmon having the same thickness. Further, lumpsuckers have a knobbly, ridged back and three large bony tubercles on each flank. Its pelvic fins form a suction disc which it uses to attach strongly to surfaces. During transport on flat surfaces without a stream of water such as on conveyor belts or slides, it is a problem that lumpsuckers can attach with their suction organ to said surfaces. This is not the case for fish not having a suction organ such as salmon.

The cultivation of lumpsuckers for later use as cleaner fish is laborious and costs intensive and so far, still dependent to a large degree on wild broodstocks caught for spawning. Re-use of lumpfish post-deployment is considered an important area where sustainability can be increased, and costs saved. Therefore, it is generally desirable to keep the cleaner fish alive and reuse them several times e.g. for different salmon production cycles or as later broodstock fish. Thus, when a fish farm is emptied and the farmed fish is transported to a processing plant, the cleaner fish such as lumpsuckers, should be paid special attention as they should be kept alive and transported to another fish plant or otherwise re-used. The lumpsuckers are fragile and must be handled more gently than farmed fish, and may not survive treatment of farmed fish, for instance with fresh water. Thus, there is a need both upon slaughter of the farmed fish but also upon treatment or other handling of the farmed fish to efficiently and gently separate the lumpsuckers from the farmed fish.

There are known solutions for instance known from NO 341228, for grading fish by size during transportation, and thereby sorting out the cleaner fish. The solutions often comprise a grid, which may have two functions, draining off water and grading fish of different size. Such a grid is well known to a skilled person, wherein the small fish falls through the grid, and the larger fish does not. NO314481 B1 discloses a grid where living fish are sorted according to their size where smaller fish fall through the grid while larger fish pass over the grid. The fish to be sorted out in such a system must however be thinner than the farmed fish, or it will not fall through the grid, unless it is shorter than the thickness of the farmed fish and flows onto the grid crosswise. As the body of the lumpsuckers are drop- or ball-like, they typically do not fall through the known grids typically used for handling of Atlantic salmon.

Furthermore, grids have the disadvantage that the sorting and transport is not in a stream of water. This is a problem for sorting of living, more vulnerable fish as lumpsuckers.

Sorting of fish is often carried out in connection with processing of dead or processed fish after slaughter or for the production food products. FR974980 A describes a solution where fish after slaughtering for further processing are transported by conveyor belts and are sorted according to their size when passing a slit between the conveyor belts. A similar solution is disclosed in JP2001304946 A for agricultural products and processed dried fish. DK1214156 T3 describes a system for sorting of particles of different size and characteristics such as during waste recycling of paper to remove stones and glass. Sorting of living fish is much more challenging and these systems are thus not suitable for the purpose of sorting live fish, in particular of different fish species having different characteristics.

It is important that sorting systems of living fish are not only designed that fish are not stressed or injured, but they must also guarantee a high degree of hygiene during the transport. It is therefore an advantage that the system can be easily and efficiently cleaned.

The main object of the invention is to separate living cleaner fish, in particular of lumpfish, from the living farmed fish, in particular salmonids, in a gentle way, keeping the cleaner fish healthy and alive. Another object is to sort and/or grade fish by size in general. Another object of the present invention is to provide a system where the fish to be sorted is in a stream of water during the sorting. A particular aim of the present invention is to provide a system which is suitable to separate lumpsuckers, which tend to attach to surfaces from salmon which tend to jump and move during transport.

SUMMARY OF THE INVENTION

The present invention relates to a system for sorting of living fish while the fish is transported from one place to another, and as the lumpsuckers are shorter than the salmon, lumpsuckers will be separated from the farmed fish.

One or more of the mentioned objects are achieved by a system, method and use as described in the independent claims. Further advantageous features and alternative embodiments are given in the dependent claims.

Thus, the present invention relates to a system for sorting of living fish, comprising an inflow section with an upstream end for receiving of fish, a gully and at least two receiving sections, wherein the gully is arranged crosswise at a downstream end of the inflow section, a first receiving section is arranged downstream of the gully for receiving fish passing over the gully, and a second receiving section is arranged below the gully receiving fish entering through the gully. The system makes use of water flow and/or gravity for transport of fish through the system. The width of the gully can be adjustable according to a predetermined length of the fish to be received in the first section. A number of guiding members can be arranged in the inflow section, in the flow direction. Preferably, the fish is transported in a stream of water. The inflow section can be in form of a grid for removal of water, waste and/or small fish. The distance between two adjacent guiding members is preferably shorter than a predetermined length of the fish to be received in the first section. The inflow section can comprise one or several grids where smaller fish under a certain thickness will be sorted out. The grid can be in form of a row of longitudinal rolls arranged in the flow direction. The distance between two adjacent rolls can be adjustable according to a predetermined thickness of the fish to be received in the first receiving section and second receiving section. Several grids with different openings can be applied and installed to achieve a higher degree of separation by thickness of fish already before passing of the gully. The guiding members can be arranged in a funnel form with the widest dimension at the upstream end of the inflow section.

The inflow section, gully, and the first receiving section are preferably subsequently arranged in a downwards inclined orientation. The inflow section, preferably having an incline of at least 2 degrees, preferably 2-7 degrees. The gully section is slanted with an incline of 60 degrees or more, allowing the fish to be transported by means of gravity and the water. The system can further comprise a sensor to determine the length of the fish upstream of the gully, and an automatized adjustment system of the gully width according to information received from said sensor.

In a further aspect the present invention relates to a method for sorting of living fish of different length, such as lumpsucker and Atlantic salmon, characterised in that a system according to any of the preceding claims is used, whereby the method comprises the following steps:

i. adjusting the width of the gully such that it is narrower than the length of the fish to pass the gully to the first receiving section,

ii. receiving fish at the upstream end of the inflow section and

iii. transporting the fish through the system and thereby sorting the fish according to their length into the first or the second receiving section.

Preferably, the at least two guiding members are arranged in the inflow section in the flow direction and wherein the method comprises an additional step of orienting the fish longitudinally in flow direction while passing the inflow section by adjusting the distance between two adjacent guiding members to a shorter distance than a predetermined length of the fish. Preferably, the fish is sorted and transported in a stream of water.

In yet a further aspect, the present invention relates to a use of the system for sorting of living fish according to differences in length, but substantially the same thickness, preferably for sorting of lumpsuckers from salmonids.

Thus, the invention relates to a system for sorting of living fish, particularly fish of different species, preferably lumpsucker and salmon, while moving the fish from one place to another. The system comprises an inflow section, optionally provided with a grid, having an upstream end receiving fish, or preferably fish and water, a gully and two receiving sections arranged downstream of the inflow section. The gully is arranged crosswise at a downstream end of the inflow section, a first receiving section is arranged downstream of the inflow section, and a second receiving section is arranged downstream of the gully. The first receiving section will receive fish flowing over the gully, and the second receiving section will receive fish falling into the gully. If a grid is present, water and small fish may fall through the grid and may be collected in a third receiving section.

The width of the gully will define the distance from the downstream end of the inflow section to the first receiving section, in flow direction. The width is preferably adjustable, as it depends on the length of the fish to be sorted. The width should be adjusted in such a way that fish shorter than a set length will fall into the gully, and fish longer than the set length will pass over the gully, because a first end of the fish will be in the first receiving section before the second end has left the inflow section. When handling farmed fish, this means that the width of the gully must be smaller for small fish, and larger for fish to be slaughtered.

The system is especially suitable for separating lumpsuckers from farmed fish such as salmonids having different length but the same principle thickness due to their characteristics in body shape. The lumpsuckers will not fall through the grid as they may be as thick as the farmed fish, but they will fall into the gully as they are considerably shorter. Preferably, the whole body of the lumpsucker will leave the inflow section before any part of the lumpsucker has reached the first receiving section, and the lumpsucker will thus fall into the gully and flow into the second receiving section. The same will occur even if the whole body of the lumpsucker is somewhat longer than the width of the gully, as is obvious to a skilled person. The fish has a certain speed through the system and might slip over the gully even though it is shorter than the set limit, but the knobbly, ridged surface of the lumpsuckers will reduce the speed of the lumpsuckers through the system. The lumpsuckers will thus slide slower over the gully than farmed salmon, and also therefore it will fall into the gully and not slip over. A skilled person would know both the size of the farmed fish and the size of the lumpsuckers in the fish farm, and therefore it is obvious to him/her how to adjust the width of the gully.

Preferably, the system has smooth contact surfaces, where the fish can easily slide on and along and which can be cleaned efficiently, guaranteeing a high degree of hygiene. Preferably, the transport surfaces incline downstream. A flat surface such as a plane conveyor belt or a transport surface having a gentle slope will increase the risk that lumpsuckers attach to the surfaces by means of their suction disc, accumulate in the system or get stuck. Thus, it is preferred that the slope of the transport surfaces in the inflow section/transport chute is at least 2 degrees, preferably 2-7 degrees. The same applies for the first receiving section. This also contributes to smoother transport of the fish by gravity. Moreover, it is preferred that the fish are transported in a stream of water. This further contributes to avoid that lumpsuckers attach to the surfaces as well as to increase fish well fare and reduce the risk of injuries during sorting and transport.

The described system has the advantage that the transport and sorting distances are short. Fish can be transported in water the whole time or only transported without water during very short periods not harmful or particularly stressing for the fish.

If the system is used in fishery, the skilled person would also know what length the fish should have in order to be kept for further processing, and thus be able to adjust the width of the gully. Smaller fish maybe returned to the sea alive and unharmed.

Thus, the current system is suitable for a careful and gentle separation of fish of different length as well as of different body shapes i.e. different species.

In order to avoid that fish may flow over the transport chute crosswise, and thus enter the gully even though it is above the set length, the system preferably comprises a number of guiding members in the inflow section. The guiding members may preferably be longitudinal baffles arranged in flow direction, above the grid/transport chute, i.e. in the upper part of the inflow section. The cross wise distance between two adjacent guiding members should preferably be shorter than the set length of the fish to be sorted out, and thus any fish being long enough not to fall into the gully will be aligned longitudinal on the grid/transport chute, and thus reach the gully with head or tail oriented first.

In a preferred embodiment, the transport chute/grid comprises a row of rolls, wherein each roll is longitudinal and extending in the transportation direction of the system. The rolls may be rotating, non-rotating, or freely suspended, depending on the context of the system and what will assist the transport and sorting of the fish. The opening between two adjacent rolls will define the size of the fish that may pass through the sorting grid, and is preferably adjustable. The opening between two adjacent rolls may increase towards the outlet of the sorting grid, either by the design of each roll, or by the design of grader as such. This will assist in the transport of the fish as well as the sorting.

The optional grid may comprise two or more sorting grids, and preferably arranged vertically above each other. The opening of each grid is smaller downstream than the opening in a grid upstream. This means that the thickest fish will not fall through any grid, and that the thinnest fish will fall through all grids. If each grid is a row of rolls, an upper grid will have a larger opening between two adjacent rolls, than a lower grid, and thus the smallest fish will be collected at the lower part of the grader and the larger fish will be collected at the upper part. In this way any fish being smaller and/or thinner than a predetermined size will fall through the grid, and any fish being shorter than a predetermined size but larger than the grid will fall into the gulley, leaving only fish larger than a predetermined width and length will be transferred to the first receiving section.

Depending on the size distribution, several grids with different openings may be applied and installed to achieve a higher degree of separation by size (thickness) of fish already before passing of the gully.

The system according to the invention may be a part of a larger system, either at atmospheric pressure, or reduced pressure, depending on the uses of the system. It may also include at least two fish tanks constituting the receiving sections for receiving the fish, a pipe system transporting the fish, means for draining off water, means for creating a water flow and possibly means for creating and maintaining reduced pressure in the system. The pipe system is transporting the fish from a pool of fish and water onto the inflow section, optionally with a grid and finally from the inflow section and gully into the fish tanks. The fish tanks inflow section and gully may be connected to each other in such a way that a closed system is made.

In the present invention the system is described in relation to a fish farm, and to separate farmed fish such as salmon and/or trout from lumpsuckers, but the system may also be used to sort other types of living fish, for instance upon pelagic fishery. The fish and water are transported to the inflow section or from a "pool of fish and water" which may be a seine, trawl, fish cage, tank, or similar. The ocean may also be a "pool of fish and water".

The pipe system may further comprise a pipe that runs down into the pool of fish and water, and when the system is running with a reduced pressure inside the system, suction will arise in the pipe, and water and fish will start to flow into the pipe. This will continue as long as there is reduced pressure inside the system. As described above the system may also be used at atmospheric pressure using well known fish pumps to pump fish and possible water into the inflow section or onto the grid.

Preferably, the system makes use of gravity for transport of fish through the system. The water maybe drained away before the fish enter the system or in the inflow section. However, for the reasons described above, it is an advantage that the fish are transported in a stream of water. The system may be equipped with water supply such as water nozzles to facilitate transport of the fish, and to reduce friction during transport. The different elements of the system are preferably arranged in an inclined way such that the fish slide through the system without any need for further transport means.

DETAILED DESCRIPTION OF THE EMBODIMENT SHOWN IN THE FIGURES

The invention will now be described with the help of the enclosed figures, showing a principle diagram of a system according to the present invention. The different parts of the figure are not necessarily in scale to each other, as the figures are merely for illustrating the invention. Relative terms such as upstream and downstream, under, above, behind, below refer to the system when installed and to the main flow direction of the fish when transported through the system.

The following description of an exemplary embodiment refers to the drawings, and the following detailed description is not meant or intended to limit the invention. Instead, the scope of the invention is defined by the appended claims.

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. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

A gully according to the present invention can be a crosswise-arranged opened gutter, chute, longitudinal slit or longitudinal aperture whereby the gully is connected to the second receiving section.

The first and second receiving section can be any suitable container, tank, vessel, cage, pipe, or the like for collecting the fish or may be the sea. Preferably, the receiving sections comprise water. Preferably fish are transported in a stream of water.

Figure 1 shows a perspective view of an embodiment of the present invention. Figure 2 shows a vertical cross section of an embodiment of the present invention, and

Figure 3 shows a top view of the embodiment in Figure 2.

The system shown in figure 1 comprises an inflow section 10. In the shown embodiment of figure 1 this inflow section is in form of a transport chute 12 with smooth surfaces with an upstream end 4 receiving fish and water. The shown chute 12 has a number of longitudinal rollers 2, arranged in a distance from each other. At the downstream end of the chute 12, there is arranged a gully 6, extending crosswise to the longitudinal rollers 2 of the chute 12. A first receiving section 5 is downstream of the inflow section 10 on the opposite side of the gully 6, arranged to receive any fish not falling into the gully 6. A second receiving section 8, preferably comprising water, is arranged downstream of the gully 6, to receive any fish falling into the gully.

The inflow section 10 is in the shown embodiment provided with guiding means 3 in form of baffles, which are arranged above the rollers 2, in order to align any fish in the transport chute 12 longitudinal, such that the fish will enter the gully with head or tail first. The baffles together with the rollers 2 contribute to that fish having a length which extends the width of the gully 6 slit will pass over the gully 6 when oriented longitudinally in relation to their body shape. The baffles may for instance be fastened to a ceiling (not shown) of the system, or if the rollers 2 are not rotating, onto the rollers.

The distance between two adjacent rollers 2 is adjustable, according to a predetermined value of the thickness of the fish to be led to the first receiving section 5. A width 1 of the gully (see fig.2) is also adjustable according to a predetermined value of the length of the fish to be led to the first receiving section 5. The distance between two adjacent baffles 3 should be adjusted according to the width of the gully, in such a way that any fish, which should not fall into the gully 6 will be aligned with the flow direction, and not fall into the gully crosswise.

The chute 12 can be formed as a grid for pre-sorting of fish according to differences in their body thickness. Under the grid, there can be a section for receiving water and smaller fish which pass between the grid members such as the guiding rolls 2. The grid system may comprise several grids for subsequently sorting different sizes of fish having different thickness. Preferably, these are arranged above each other. The system may also be equipped with a system for water and waste treatment of waste comprised in the water.

Preferably, the inflow section 10 is provided with a chute 12 with a solid bottom having a smooth surface. The fish may enter the inflow section/grid in a stream of water with water or alternatively the water main be drained away before entering into the inflow section or when passing the grid. In case of a solid bottom of the chute 12, the living fish are preferably transported together with water through the system. This is more gentle for sorting of living fish.

The gully 6 in the shown embodiment is in form of a crosswise arranged slit, the slit extending along the whole width of the grid (crosswise to the main transport/flow direction of fish) whereby the slit is shorter in distance than the length of the fish, which are supposed to pass the gully without entering through the gully and being sorted out.

The width of the gully is preferably adjustable according to the size of the fish to be graded and sorted. In figure 1 this is done by a movable flap 20, which can be displaced as indicated by the arrows in order to adjust the width of the gully slit. The position by the flap 20 can either by adjusted manually by suitable means for adjustment such as by a mechanically connected handle 22 for controlling the flap 20 in figure 1. Alternatively, the flap may be adjusted in a semi or fully automated matter by suitable means for adjustment. In a particularly preferred embodiment, the size, in particular the length of the fish, is determined further upstream by one or more suitable sensors such as a camera, a laser measuring device or the like. Data from the sensor further up-stream measuring the size of the fish are sent to a receiver of a control unit, which in turn controls and adjusts the width 1 of the gully 6 slit in an optimised way. A comparable method may be applied for the adjustment of the distance between the rollers in the inflow section 10.

Apart from a slit, the gully 6 may have other shapes such as one or more circular or oval outlet holes having a diameter being shorter than the length of the fish that should pass the gully 6.

Guiding baffles/guide member 3 and rollers 2 maybe formed as integrated elements. They may also represent unitary elements.

The described grader system is particularly suitable for separation of cleaner fish, preferably lumpsuckers, and farmed fish such as Atlantic salmon e.g. before treatment of the farmed fish such as for delousing, or slaughtering.

The function of the optional embodiment with a grid in the inflow section 10 can be to remove water and optionally to remove smaller fish to be sorted out.

Furthermore, the design of the grid may contribute that fish to be received by the first receiving section after the gully 6 are oriented with the head or tail first in order to avoid that they will enter the gully 6 crosswise in case the gully is in form of a gutter/slit.

The advantage of the described system is an effective separation of different fish species based on differences in length of the fish. The system is particularly suitable to grade fish in cases where the thickness of the fish is similar due to their characteristic body shape while the length differs. The system allows to grade fish without harming them and takes care of the fish well fare.

A further advantage of the system is the possibility to adjust the size of the grading elements such as the distance between the guiding rollers and the gully width allowing to effectively sort out fish of different size.

Figure 2 shows schematically a cross section view through an embodiment according to the present invention. Fish of different length enter the device at the upstream end 4 of the inflow section 10. After the inflow section, the fish proceed either over the gully 6 to enter the first receiving section 5. These are fish that typically have a body length being longer than the width of the gully. The fish being shorter than the width of the gully 6 will fall into the slit of the gully and enter the receiving section 8.

Figure 3 shows a top view of an embodiment according to the present invention. In the shown embodiment the inflow section provided with rollers 2 arranged longitudinally in flow direction. Also comprised are baffles as guiding members 3 for orienting of inflowing fish.

Preferably, the system makes use of water stream and/or gravity for transport of fish through the system. Preferably, no further transport means, such as conveyor belts or the like, are needed to advance the fish through the system.

Preferably, the system is provided with smooth contact surfaces, where the fish can easily slide on and along and which can be cleaned efficiently. Preferably, the transport surfaces incline downstream. A flat surface such as a plane conveyor belt or a transport surface having a gentle slope will increase the risk that lumpsuckers attach to the surfaces by means of their suction disc and get stuck. Thus, it is preferred that the slope of the transport surfaces is at least 2 degrees, preferably in the range of 2 to 7 degrees.

Moreover, it is preferred that the fish are transported in a stream of water. This further contributes to avoid that lumpsuckers attach to the surfaces as well as to increase fish well fare and reduce the risk of injuries during sorting and transport.

The described system has the advantage that the transport and sorting distances are short and that the sorting time is short. This is least stress- and harmful for the fish. Fish are transported in water or are only transported without water during very short periods not harmful or particularly stressing for the fish.

The described system is suitable for sorting of living fish, in a careful and not stress full way and allows a high degree of hygiene.

Claims (18)

1. System for sorting of living fish, comprising an inflow section (10) with an upstream end (4) for receiving fish, a gully (6) and at least two receiving sections (5, 8) characterized in that the gully (6) is arranged crosswise at a downstream end of the inflow section (10), a first receiving section (5) is arranged downstream of the gully (6) for receiving fish passing over the gully (6), and a second receiving (8) section is arranged below the gully (6) receiving fish entering through the gully (6) wherein the system makes use of a water flow and/or gravity for transport of fish through the system.

2. System according to claim 1, wherein the width (1) of the gully (6) is adjustable according to a predetermined length of the fish to be received in the first section (5).

3. System according to claim 1 or 2, wherein a number of guiding members (3) are arranged above the inflow section (10), in the flow direction.

4. System according to any of the claims 1 to 3, wherein the fish is transported in a stream of water.

5. System according to claim 3 or 4, wherein a distance between two adjacent guiding members (3) is shorter than a predetermined length of the fish to be received in the first section (5).

6. System according to any of the preceding claims wherein the inflow section comprises one or several grids where smaller fish under a certain thickness will be sorted out.

7. System according to 6, wherein the grid is in form of a row of longitudinal rolls (2) arranged in the flow direction.

8. System according to claim 6, wherein the distance between two adjacent rolls (2) is adjustable according to a predetermined thickness of the fish to be received in the first receiving section (5) and second receiving section (8).

9 System according to any of the claims 6 to 8, wherein several grids with different openings are applied and installed to achieve a higher degree of separation by thickness of fish already before passing of the gully.

10. System according to claim 5, wherein the guiding members (3) are arranged in a funnel form with the widest dimension at the upstream end (4) of the inflow section (10).

11. System according any of the preceding claims, wherein the inflow section (10), and the first receiving section (5) are subsequently arranged in a downwards inclined orientation, preferably having an incline of at least 2 degrees, more preferably of 2-7 degrees.

12. System according to any of the preceding claims, wherein the gully (6) has an incline of at least 60 degrees.

13. System according to any of the preceding claims wherein the system further comprises a sensor to determine the length of the fish upstream of the gully (6), and an automatic adjustment system of the gully width (1) according to information received from said sensor.

14. Method for sorting of living fish of different length, such as lumpsucker and Atlantic salmon, characterised in that a system according to any of the preceding claims is used, whereby the method comprises the following steps:

i. adjusting the width of the gully (6) such that it is narrower than the length of the fish to pass the gully (6) to the first receiving section (5),

ii. receiving fish at the upstream end (4) of the inflow section (10) and iii. transporting the fish through the system and thereby sorting the fish according to their length into the first (5) or the second receiving section (8).

15. Method according to claim 14, wherein at least two guiding members (3) are arranged above the inflow section (10) in the flow direction and wherein the method comprises an additional step of orienting the fish longitudinally in flow direction while passing the inflow section by adjusting the distance (7) between two adjacent guiding members (3) to a shorter distance than a predetermined length of the fish.

16. Method according to claim 14 or 15, wherein the fish is transported in a stream of water.

17. Use of a system according to any of the claims 1-13 for sorting of living fish according to differences in length and having substantially the same thickness.

18. Use according to claim 17 for sorting of lumpsuckers from salmonids.