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Title:
METHOD FOR DISTINGUISHING ALIVE AND DEAD FISH
Document Type and Number:
WIPO Patent Application WO/2018/169412
Kind Code:
A1
Abstract:
A method, device and system for separating living fish from dead fish are described. Also, applications of the method and device to sort living fish from dead fish after the treatment of fish, such as disease treatment or removal of lice in a net cage are described.

Inventors:
HAUGE, Mons-Ove (Blænesvegen 175, 5396 Vestre Vinnesvåg, 5396, NO)
Application Number:
NO2018/050075
Publication Date:
September 20, 2018
Filing Date:
March 16, 2018
Export Citation:
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Assignee:
SERVICEBÅT AS (Blænesvegen 175, 5396 Vestre Vinnesvåg, 5396, NO)
International Classes:
A01K61/95; A01K61/13; A22B3/08; A22C25/04; A22C25/08; B07C5/34
Domestic Patent References:
WO2012064201A12012-05-18
Foreign References:
US20100081961A12010-04-01
EP1143802B12004-12-08
US20060292550A12006-12-28
GB2543924A2017-05-03
Attorney, Agent or Firm:
ACAPO AS (P.O. Box 1880 Nordnes, 5817 Bergen, 5817, NO)
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Claims:
Claims

1 . Method for separating living (B) and dead (C) fish, characterised in that the method comprises the following steps;

i) the fish (B + C) receive electrical stimulus set up so that living fish (B) are responsive to said electrical stimulus and become rigid, while dead fish (C) do not respond to said electrical stimulus and remain limp,

ii) living (B) and dead (C) fish are then separated based on whether the fish after said electrical stimulus is rigid or limp.

2. Method according to claim 1 , characterised in that said electrical stimulus has a power, frequency and duration sufficient to allow the living fish (B) to be responsive to said electrical stimulus and become rigid. 3. Method according to any of the preceding claims, characterised in that said electrical stimulus has a power, frequency and duration so that dead fish are not responsive to the electrical stimulus and remain limp.

4. Method according to any of the preceding claims, characterised in that said electrical stimulus is applied by an electric treatment unit (21 ), and that fish are automatically fed to the electrical treatment unit by a transport device (19), and that the speed of the transport device 19 regulates the duration of the electrical treatment. 5. Method according to any of the preceding claims, characterised in that after electrical stimulus the fish (B + C) are led across an opening (23), where the size of the opening (23) is set up so that rigid fish (B) pass across the opening (23) while limp fish (C) fall through the opening (23). 6. Method according to any of the preceding claims, characterised in that the time interval after electrical stimulus and before the fish (B + C) reach the opening (23) can be adjusted.

7. Method according to any of claims 1 -3, characterised in that the fish are separated after electrical stimulus in that one depicts the fish (B + C) with image or video means and separates the fish according to whether it is rigid or limp. 8. A method according to claim 7, characterised in that the fish (B + C) by electrical stimulus is uniquely identified and that this identification is later used to distinguish whether the fish was rigid or limp during the electrical stimulation.

9. Method according to claim 1 for the emergency processing of fish at a fish farm site, characterised in that the method comprises the following steps;

i) living fish (B) and dead fish(C) are retrieved from a net cage (10),

ii) electrical stimulus is applied to fish (B + C), set up so that living fish (B) are responsive to said electrical stimulus and become rigid, while dead fish (C) are not responsive to said electrical stimulus and remain limp,

iii) living (B) and dead (C) fish are then separated based on whether the fish after said electrical stimulus is rigid or limp.

10. A method according to claim 10, characterised in that the living fish (B), after step (iii) are emergency slaughtered.

1 1 . Method according to claim 9, characterised in that the fish (B + C) are retrieved from the net cage (10) after the starting of an active treatment of the fish in the net cage (10). 12. Method according to claim 1 1 , characterised in that said active treatment is any treatment intended to prevent or treat disease, but can result in that the living fish are injured or weakened.

13. Method according to claim 12, characterised in that said active treatment is selected from the group consisting of;

- treatment or prevention of disease with chemicals or functional feed, - treatment or prevention of attacks and infection by parasites with chemicals or functional feed

- mechanical treatment to prevent attacks and infection by parasites,

- crowding of fish caused by tidal currents, weather, misuse of the equipment, or by crowding and/or the pumping of fish for discharging fish from the net cage.

14. Method according to claim 13, characterised in that said parasites are ectoparasites.

15. Method according to claim 14, characterised in that said ectoparasites are lice, such as salmon lice.

16. Method according to any of the preceding claims, characterised in that samples of fish (B + C) from the net cage are made continuously after the start of an active treatment such that the fish are quickly and continuously fed to the unit in step (ii) and subsequent emergency slaughtered in step (iv).

17. Method according to any of claims 1 to 16, characterised in that the muscle response of the living fish (B) from electrical stimulation is quantified, and said quantified muscle response is correlated with a parameter of quality for the fish or fish meat.

18. Device (20) for separating living fish from dead fish, characterised in that the device (20) is comprised of an electrical treatment unit (21 ) and a sorting unit (22), where the electrical treatment unit (21 ) subjects fish to an electric stimulus, and where the sorting unit (22) sorts fish according to the rigidity of the fish.

19. Device (20) according to claim 18, characterised in that the electrical treatment unit is comprised of a number of electrodes which apply current to the surface of the fish (B + C).

20. Device (20) according to claim 18, characterised in that the device (20) is comprised of a transport appliance (19) for transporting fish to and through the device (20). 21 . Device (20) according to claim 20, characterised in that a first set of

electrodes is arranged on the conveyer belt (19) of the transport appliance and a second set of electrodes is arranged hanging above the conveyor belt (19), set up so that as the fish (B + C) pass through the treatment unit (21 ) they come into contact with both sets of electrodes and sufficient current is applied for the living fish to become rigid.

22. Device (20) according to any of the claims 18-21 , characterised in that the sorting unit (22) is an integrated part of the conveyor belt (19), while said conveyor belt (19) is equipped with one or more openings (23).

23. Device (20) according to claim 22, characterised in that said opening (23) has a size that is set up such that living electrically treated, rigid fish (B) are led across the opening (23) while the electrically treated, limp dead fish (C) are led into the opening (23).

24. Device (20) according to any of the claims 18 to 23, characterised in that the device (20) is comprised of a positioning unit upstream of the electrical treatment unit (21 ) and set up so that the fish (B + C) which are fed to the electrical treatment unit (21 ) have a predetermined direction and position on the conveyor belt (19).

25. Device (20) according to any of the claims 18-24, characterised in that the device (20) is comprised of a water drainage unit (18) such as a separation bin (18) for the drainage of water before the fish (B + C) are fed to the electrical treatment unit (21 ).

26. Device (20) according to claim 18, characterised in that the sorting unit is comprised of image or video means, and that the fish are separated after electrical stimulus by depicting the fish (B + C) by image or video means and separating the fish depending on whether they are rigid or limp.

27. Device (20) according to claim 26, characterised in that the unit is comprised of an identification unit and that, by electrical stimulus, the fish (B + C) are uniquely identified and that this identification is later used to distinguish whether the fish was rigid or limp during electrical stimulation.

28. System for the emergency processing of fish at a fish farm site, characterised in that the system is comprised of;

- a device for retrieving and transferring living fish (B) and dead fish (C) from a net cage (10),

- a device (20) which is comprised of an electrical treatment unit (21 ) and a sorting unit (22), where said electrical treatment unit (21 ) subjects the fish to an electrical stimulus, and where the sorting unit (22) sorts fish depending on the rigidity of the fish

- a separation unit for separating living fish (B) from dead fish (C)

- a device for the emergency slaughter of said living fish (B). 29. System according to claim 28, characterised in that the device (20) for retrieving and transfer of living fish (B) and dead fish (C) from the net cage (10) comprises a collector (14) and pipeline (16) to lead the fish (B + C) to the surface, and where the collector (14) is arranged in the net cage (10) just before an active treatment of the fish in the net cage (10) starts.

30. System according to claim 28, characterised in that the retrieval of fish (B + C) from the net cage (10) is done continuously after the initiation of an active treatment so that the fish (B + C) are rapidly and continuously led to the device for the determination of whether they are alive or dead, and subsequent emergency slaughter of the living fish (B).

Description:
METHOD FOR DISTINGUISHING ALIVE AND DEAD FISH Field of the Invention

The present invention relates to a method, device and system for separating living fish from dead fish. In one embodiment, the method is used for emergency processing of fish at a fish farming site.

Background of the Invention.

Fish farmed in installations are susceptible to parasites and disease, amongst other things, after attacks from pathogenic organisms. For the prevention of, or treatment against, parasites and diseases the fish is provided with a treatment such as a chemical treatment with various medical substances. The treatment can also be mechanical, such as the removal of salmon lice which currently represents a significant problem for the fish farming industry. Due to technical reasons related to fish farming, even large food fish can undergo a mechanical sorting to separate specific size-sorting of different fish and thus slaughter the fish by the correct size according to the market demand at a given time. During such a treatment the fish can be subject to damage and accidents, and a portion of the fish will be so reduced to the extent that they will sink to the bottom of the net cage and subsequently be collected and treated as dead fish. Similar situations can occur by the crowding of fish in the net cage for retrieval for transport and slaughter.

The reduced fish, i.e. a fish that is so reduced that it does not swim freely in the net cage but sinks towards the bottom of the net cage is however still alive in the net cage. It is often referred to as "dying" since it collects at the bottom of the net cage with the already dead fish. It will thus be treated as dead fish, and after some time it will probably expire.

Today, known systems can remove dead fish and other debris which accumulate at the bottom of a net cage. An installation which has been widely used is the collector from LiftUp AS, and such systems are, among others, described in WO2012/064201 and NO339199. A collector is arranged at the bottom of the net cage. The collector generally has a conical bottom side which lies against the net cage wall. Dead fish and dying living fish congregate in the area around the collector, and a pressure ejector pump allows the fish (which is considered to be dead) to be transported to the surface for removal and treatment. Normally the collector is emptied one day after a treatment for lice removal or treatment for disease or any other cause of treatment, which enables the removal of the fish, which due to the treatment have been so weakened that they end up in the area around the collector.

However, it has been shown that a large proportion of the fish that end up in the area around the collector are still alive for a considerable time yet will still be collected by the collector and as such treated as dead fish.

Such dying fish suffer today under the conditions by dying due to expiration in net cages or being pumped into a separation bin on a float or boat or expire in tubs and pans before they are put in a mill and milled together with acid to silage.

It is an aim of the present invention to be able to separate living fish from dead fish. The invention can be used to separate living fish from dead fish, such as those collected with such a collector in a net cage. The living fish will be slaughtered (emergency slaughtered), and can be used for consumption, preferably human consumption. The dead fish will be treated as dead fish and will go for silage or other appropriate treatments.

It is an aim of the present invention that living fish and dead fish are to be separated continuously. This means fish which end up in the area around the collector are continuously and regularly led to the surface and separated into at least two groups; living fish and dead fish.

It is thus an aim of the present invention to retrieve living fish from a fish farming site, such as a farming net cage, and to process the fish before it expires. When retrieving living fish, there is a risk of retrieving fish which are already dead, i.e. fish which have recently died due to expiration in the fish farm net cage, thus an aspect of the invention aims to be able to sort living fish from dead fish.

It is a further aim of the invention that one can document that living fish which are retrieved, and which can undergo emergency slaughter, are actually alive.

Today there are vessels at fish farming sites which conduct ordinary process slaughter of fish at the net cage edge. An example of such vessels is Tauranga, which operates for Marine Harvest. These vessels and operations, however, are for the ordinary harvesting of fish that are alive, and which swim freely around in the net cage, and which are slaughtered in accordance with a pre-planned schedule.

Furthermore, there are known systems for the retrieval of dead fish. So-called collectors are often used and positioned at the bottom of the net cage. An example of such a collector is the LiftUp-collector. This collector is arranged in the net cage installation and gathers up all the dead fish, and/or other waste from the net cage. Living dying fish will also end up in this collector.

The present invention will provide a new solution where one collects this group of both dead and living fish, and quickly emergency slaughter the living fish before likely expiration occurs. Today there are no good methods and routines for the sorting, treating and quick euthanisation of injured fish.

In addition, the fish farmers suffer huge economic losses as a result of too many fish (i.e. also living, probably dying fish) being treated as dead fish. Today, one must currently pay for the collection and disposal of dead fish. With the present invention, a substantial proportion of the fish, which was previously considered dead or dying, is actually shown to be living and could possibly be used for more high-value products which one can get paid for.

Thus, it is an aim of the present invention to provide a method and system for extracting dying yet living fish as a resource. In this way one can, for example, sort out the proportion of fish suitable for i) human consumption, ii) fresh, high quality residual raw material, and iii) fodder/silage. Fish which is emergency slaughtered will fall into the categories i) and ii), and already dead fish collected from the collector, will fall into category 3. With today's solutions all fish which are damaged, reduced or die when receiving active treatment and are collected by the collector falls into category 3. It is thus an aim of the present invention that the fish which are collected are to be categorised into categories i) and ii).

Thus, it is an aim of the present invention to extract the fish which have not died from being transferred from the collector. These living fish are separated from possibly already dead fish. Currently, there are known different systems for stunning and/or killing fish with electrical treatment. For example, it is known from EP1 143802 that applying electrical anaesthesia to fish reduces the stress levels of the fish prior to being slaughtered. It is also known that one can apply electrical treatment powerful enough that the fish dies.

It is also known that living fish, when given electrical treatment, respond to the treatment, while fish that are dead are not responsive to electrical treatment. When the fish is given a sedating (or killing) electrical treatment it will, in addition to losing all consciousness, respond with a general contraction of the bodily muscles.

Therefore, during electrical treatment, the fish that was alive when the treatment started, will be rigid. Dead fish that are subject to the same electrical treatment will not respond to treatment and remain limp. Fish muscles, during cardiac arrest, no longer receive oxygen by blood perfusion, and will over time lose the ability to contract. This is a graded response that will decrease as a function of time after the cardiac arrest, temperature, and ATP stores in the muscle. Both water temperature and the level of fatigue of the fish will therefore be able to affect how long after the cardiac arrest the muscle will be responsive to the electrical treatment. Furthermore, current and frequency will affect the contraction.

Summary of the Invention

The present invention relates to a method for separating living (B) and dead (C) fish, wherein the method is comprises the following steps;

i) electrical stimulus is applied to the fish (B + C) and adapted so that living fish (B) are responsive to said electrical stimulus, and become rigid, while dead fish (C) do not respond to said electrical stimulus and remain limp, ii) living (B) and dead (C) fish are then separated based on whether the fish, from said electrical stimulus, are rigid or limp.

In one embodiment, the said electrical stimulus has an effect, frequency and duration sufficient for living fish (B) to be responsive to said electrical stimulus and become rigid.

In one embodiment, said electrical stimulus has an effect, frequency and duration so that dead fish are not responsive to electrical stimulus and remain limp.

In one embodiment, said electrical stimulus of an electrical treatment device is applied, and that fish are automatically led to the electrical treatment device by a transport arrangement and that the speed of the conveyor unit regulates the duration of the electrical treatment.

In one embodiment, the fish (B + C) are led, at electrical stimulus, over an opening, where the size of the opening is adjusted such that rigid fish (B) pass over the opening while limp fish (C) fall through the opening.

In one embodiment, the time interval after electrical stimulus and before the fish (B C) reach the opening can be regulated. In one embodiment, the fish are separated at electrical stimulus by displaying the fish (B + C) by image or video means, and the fish are separated depending on whether they are rigid or limp. In one embodiment, the fish are uniquely identified by electrical stimulus, and this identification is later used to distinguish if the fish was rigid or limp during the electrical stimulation.

In one embodiment, the method is used for the emergency processing of fish at a fish farming site, wherein the method comprises the following steps;

i) living fish (B) and dead fish (C) are retrieved from a net cage,

ii) electrical stimulus is applied to the fish (B + C) and is adapted so that living fish (B) respond to said electrical stimulus, and become rigid, while dead fish (C) are not responsive to said electrical stimulus and remain limp,

iii) living (B) and dead (C) fish are then separated based on whether the fish at said electrical stimulus are rigid or limp.

In one embodiment, the fish(B) are emergency slaughtered after step (iii). In one embodiment, the fish (B + C) are retrieved from the net cage after the start of an active treatment of the fish in the net cage.

In one embodiment, said active treatment is every treatment intended for preventing or treating disease, but which can result in living fish being damaged or reduced.

In one embodiment, said active treatment is chosen from the group consisting of;

- treatment or prevention of disease with chemicals or functional feed,

- treatment or prevention of attacks and infection from parasites with chemicals or functional feed

- mechanical treatment to prevent attack and infection from parasites,

- crowding of fish caused by tidal currents, weather, misuse of equipment, or by crowding and/or by pumping of fish for discharge from the net cage. In one embodiment, said parasites are ectoparasites.

In one embodiment, said ectoparasites are lice, such as salmon lice. In one embodiment, fish (B + C) are retrieved continuously from the net cage after the start of an active treatment, so that the fish quickly and continuously are fed to the determination in step (ii) and subsequent emergency slaughter in step (iv).

In one embodiment, living fish (B) are quantified by muscle response after electrical stimulation and said quantified muscle response is correlated to a parameter of quality for the fish or fish meat.

The present invention relates in a second aspect to a device for separating living fish from dead fish, characterised in that the device is comprised of an electrical treatment unit and a sorting unit, where the electrical treatment unit subjects fish to an electrical stimulus, and where the sorting unit sorts the fish according to the rigidity of the fish.

In one embodiment, the electrical treatment unit comprises a number of electrodes which apply current to the surface of the fish (B + C).

In one embodiment, the device comprises a transport arrangement for the

transportation of fish to and through the device. In one embodiment, the device comprises a first set of electrodes arranged on the conveyor belt of the transport arrangement and a second set of electrodes is arranged hanging over the conveyor belt, adapted so that the fish (B + C), as they pass through the treatment unit come into contact with both sets of electrodes and sufficient power is applied for the living fish to become rigid.

In one embodiment, the sorting unit is an integrated part of the conveyor belt as the conveyor belt is equipped with one or more openings. In one embodiment, said opening has a size which is adapted so that living, electrically-treated, rigid fish (B) are led across the opening while the electrically- treated, limp dead fish (C) is led through the opening. In one embodiment, the device comprises a positioning unit upstream of the electrical treatment unit and adapted so that the fish (B + C) which are fed to the electrical treatment unit has a pre-determined direction and position on the conveyor belt. In one embodiment, the device comprises a water draining unit such as a separation bin for the drainage of water before the fish (B + C) is led to the electrical treatment unit.

In one embodiment, the sorting unit comprises of image or video means, and where the fish are separated by electrical stimulus by depicting the fish (B + C) using image or video means and dividing the fish depending on whether they are rigid or limp.

In one embodiment, the device is comprised of an identification unit, and that the fish (B + C) are uniquely identified by electrical stimulus and that this identification later is used to distinguish whether the fish was rigid or limp during the electrical stimulation.

The present invention also relates to a system for emergency processing of fish at a fish farming site, characterised in that the system comprises;

- a device for retrieving and transferring living fish (B) and dead fish (C) from a net cage

- a device comprising an electrical treatment unit and a sorting unit, where the electrical treatment unit subjects fish to electrical stimulus, and where the sorting unit sorts the fish depending on the rigidity of the fish

- a separation device for separating living fish (B) from dead fish (C)

- a device for the emergency slaughter of said living fish (B). In one embodiment, the device for retrieving and transferring living fish (B) and dead fish (C) from the net cage comprises a collector and pipeline for leading the fish (B + C) to the surface, and where the collector is arranged in the net cage just prior to beginning an active treatment of the fish in the net cage.

In one embodiment, retrieval of fish (B + C) from the net cage is carried out continuously after the beginning an active treatment, so that the fish (B + C) rapidly and continuously are fed to the arrangement for determining whether it is alive or dead, and subsequent emergency slaughter of living fish (B).

Preferred embodiments of the invention shall in the following be described in more detail with reference to the accompanying figures, where:

Figure 1 shows schematically a system in which the fish are removed from the net cage via a collector, and where the living and dead fish, at electrical treatment, are separated and where living fish are emergency slaughtered.

Figure 2a shows in more detail the electrical treatment device and the sorting device according to the invention. Figure 2b shows how electrically treated living fish pass across an opening in a conveyor belt, while figure 2c shows how electrically treated dead fish fall through an opening in the conveyor belt.

Description of preferred embodiments of the invention. As indicated above, the present invention relates to the separating of living fish from dead fish. The method and device according to the invention can generally be used for sorting living fish from dead fish. However, the invention is exemplified with a method relating to a fish farming installation where one retrieves dead and living fish, and where it is desirable to separate them into two different groups.

There are currently no good methods for the rapid killing of injured and dying fish. One of the reasons that such methods do not exist today is that in a fish farm installation there are a vast number of individuals, and there are no solutions to pick out the fish that are injured but alive.

The present invention relates to the general retrieval of injured living fish from a fish farm site. However, we know that active treatment of fish, such as mechanical delousing, will cause increased mortality the first few days after treatment. In some cases, several percent of the fish die after treatment, but on average the mortality rate from the mechanical treatment of fish is around 1 %. Regardless, there is a large volume of fish which die, and which could be used for consumption provided that they were emergency slaughtered before they expire.

After the fish has been retrieved from the net cage, or any other fish farm site, they are subjected to a treatment in which they are sorted into at least two groups; living fish and dead fish. One has documented from parallel investigations that the fish being sorted to the "living" group actually were alive when they were retrieved from the net cage, and that the fish meat after slaughter meets current quality

requirements. In some cases, the living fish can be separated into several groups, where each group provides fish meat after given quality criteria. Figure 1 shows schematically a fish farm net cage 10 for the farming of fish. The net cage 10 is equipped with a net cage bag 12, and in the bottom section 12a of the net cage bag 12 a collector 14 is arranged. The fish which are dead, or which are so reduced that they cannot swim freely within the net cage 10 will sink down towards the bottom section 12a of the net cage 10, to the area of the collector 14, and are collected by the collector 14. The fish can be pumped or otherwise moved via a hose or a pipeline 16 to a position at the surface, for example, to a vessel or a raft for further processing.

The fish can be collected from the fish farm net cage with a collector 14. This is often a collector of a LiftUp type, which provides a gentle transferral of the fish from the bottom of the net cage 10 to the surface. It should be emphasised that the net cage can be of any type, for example, floating open net cages, floating watertight net cages, land based net cages or offshore based net cages. The principle is that the fish (both living, reduced or otherwise injured fish, and dead fish) are led from the net cage to a device for the processing and sorting of the fish, such as sorting of, respectively, living and dead fish.

Figure 1 shows how the fish which are led to the surface are transferred to one or more conveyor belts 19 for transportation to the treatment device 20. Preferably water is drained from the fish through a separation bin 18 or a corresponding water drainage unit 18, by drainage 18a. It is preferable that the fish which is sent to the treatment device is not in water.

Figure 1 also shows schematically fish in the net cage, and fish which are subjected to treatment for sorting. To illustrate, the following categories are used;

A - healthy and freely swimming fish

B - living fish, but reduced or injured and probably "dying"

C - dead fish

E - living fish The living fish A swim freely in the net cage 10 even after the fish has been treated mechanically or chemically for pathogenic organisms. Some of the fish are injured and weakened by the treatment, and this fish are termed as B and sink to the bottom of the net cage and are collected via the collector 14. Dead fish C can also be collected in the collector. Dead fish C and living fish B are then led together to the treatment and sorting device 20.

Since the part of the fish that was living when they reached the collector 14 is to be used for human consumption, it is preferable that the collection of fish is gentle. It is currently preferable to conduct the collection of fish from the collector by air lift. The treatment and the sorting device 20 consists in the main of two components; i) an electrical treatment unit 21 which subjects the fish to an anaesthetising electric shock, and

ii) a sorting unit 22

The fish B + C are fed by a conveyor belt 19 to a unit 21 which subjects the fish B+C to an electric shock to stun the fish. The voltage and/or frequency is sufficient for the fish B + C to obtain sufficient contraction for the fish to be sorted in the sorting unit 22.

The fish will respond differently to electrical stimulus depending on whether it is alive or dead. The clarification of whether the fish is dead or alive from electrical stimulus that leads to reactions such as rigidity or limpness, becomes clear while the fish are subjected to electrical stimulus. The criteria for sorting the fish must also be performed while the electrical stimulus is applied, i.e., photos/video/laser/sensor must be taken when the electrical stimulus is applied, or the electrical stimulus must remain sufficient for the fish, depending on whether it is rigid or limp, to be sorted on a conveyor belt afterwards. We have conducted a series of experiments to confirm that the electrical stimulation works sufficiently to separate the living fish from the dead fish which are retrieved from a fish farm net cage. The purpose of the experiments was to investigate whether fish that would normally expire during and after delousing with a

thermomechanical delouser, could be retrieved from the bottom of the net cage and checked for life by electrical stimuli. It was decided to use electric central stimulus by electrodes in the head region of the fish.

Upon arrival at the relevant fish farm installation, a well boat with thermomechanical delousing was already on site. All the fish from a net cage was forced and pumped into the well of the boat. Subsequently, it was inspected whether the net cage was free of dead fish, such that the overlying dead fish would not be counted in the investigation. The fish were then pumped from the well-boat through the delouser and back into the net cage. The whole operation from crowding till all the fish were back took approximately 8 hours. We began the pumping up of fish from the bottom of the net cage about 3 hours after the return pumping from the well-boat had started. The net cage "lift-up" was used with a flexible hose of about 30 cm in diameter. A large compressor on the deck of the service boat produced compressed air which provided an airlift and suction in the collector.

In the first experiment, about 30 fish were pumped up from the bottom of the net cage. All of these had been at the bottom of the cage for between 0 and 3 hours, probably closer to 3 hours. The fish were then placed individually in an electrical anaesthesia apparatus where the voltage could be steplessly controlled up to 230V. 20V showed strong muscle contraction. This is an acceptable method for

anaesthesia in slaughterhouses and is followed by exsanguination as a method of slaughter. With electrical anaesthesia, fish will immediately lose all consciousness and will not be able to be resuscitated (brain dead).

The results from the study showed that:

i) Almost all the fish (98%) which were pumped up from the bottom of the net cage bag, and which, by the farmer were characterised as lost, showed clear visual signs of life after being pumped up on the deck of service boat.

ii) Living and living injured salmon can easily be pumped up from the bottom of the net cage using an air lift

iii) Electrical stimulation can be used as a sorting criterion for dead and living fish

Additional experiments have shown that all frequencies and current types will serve as electrical stimulus, and the voltage can range between 5 V-10.000 V.

A presently preferred embodiment of the electrical treatment unit 21 is a device as given in NO323882, i.e. where the fish are passed via a channel or conveyor belt to be in contact with at least two electrodes of a different voltage, so that a voltage is applied directly on the surface of the fish B + C. It should be emphasised that the present invention is not limited to which electrical treatment unit 21 is used, and that one with the invention can in principle use any electrical treatment unit 21 which subjects the fish to sufficient electromagnetic anaesthesia or shock such that the muscle contraction of the fish is affected. With such a treatment fish B who were alive when the treatment started will become rigid, whereas fish C which had died when the treatment started are not affected and remains limp.

A presently preferred embodiment of the sorting unit 22 is a conveyor belt with openings 23. The openings 23 have a size such that fish C which were dead when the treatment started, because the fish C are limp, will fall through the opening 23, whereas fish B which were alive, and have become rigid by the electrical treatment will be led across the opening 23 and remain on the conveyor belt 19. These fish will be emergency slaughtered in a known manner, for example, by exsanguination (not shown).

Figure 2a shows schematically, in more detail, the treatment and sorting unit 20. Figure 2a shows how fish, both living B and dead C are transferred via a transport device 19 through the treatment and sorting unit 20 to be able to separate living from dead fish. The fish are automatically led towards electrodes which apply a current to the fish such that the fish receive a shock and are electrically stunned. This treatment will, depending on whether the fish was alive B or dead C when the electro treatment started, provide fish with a varying rigidity. This property, i.e. varying degrees of rigidity is used to sort the fish B and the fish C apart. Figure 2a also shows schematically how an opening 23 in the conveyor belt 19 is used to separate fish B and fish C from each other, depending on the degree of rigidity of the fish. Figure 2c shows how fish C, which were dead before electrical treatment, are sufficiently limp or bendable for them to fall down through the opening 23, while figure 2b shows how fish B which are more rigid are led across the opening 23 and out with the conveyor belt 19. The amount of current or voltage that must be administered to achieve adequate rigidity on living fish B for it to be separated from dead fish C will be determined by experiments. Likewise, the speed of the conveyor belt can vary, so that the fish can get a predeterminable residence time in the electrical treatment unit 21 , sufficient to allow the fish, as they pass across the opening 23, to be rigid if they were alive B when the treatment started. The size of the opening 23 may also be varied such that rigid fish B pass the opening 23 while limp fish C fall through the opening 23.

The present invention relates in one aspect also to a method to sort living fish from dead fish. As mentioned above, the response from the electrical stimuli may be graded, and the effect can be different depending on which phase in the death process the fish is in, i.e. in which phase on a scale from healthy swimming to unresponsive dead. For treatment against, for example, salmon lice one would typically collect fish one day after the delousing treatment. Before delousing treatment begins, one

assembles a collector 14 in the net cage bag 12. Optionally, one can empty the existing collector 14, before the delousing treatment begins. One should only get fish that are dead or injured/weakened after the delousing treatment has started.

Furthermore, the transfer of the fish from the collector 14 to the treatment unit 20 should be continuous. With today's treatment, the collector is emptied not before one day after treatment, and then close to all the fish will have died. However, the principle underlying the present invention is that one should sort out the fish that are alive when they arrive at the collector 14 and treatment unit 20, and then it is important that the transfer is done continuously and regularly.