GB2417408A

GB2417408A - Device for electrically slaughtering fish

Info

Publication number: GB2417408A
Application number: GB0419123A
Authority: GB
Inventors: John Ace-Hopkins
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-08-27
Filing date: 2004-08-27
Publication date: 2006-03-01
Anticipated expiration: 2024-08-27
Also published as: GB0419123D0; GB2417408B

Abstract

The device has a stunning station 1 for stunning the fish using an electric current, and a stun maintenance station 6 which uses an electric current to maintain the fish in an unconscious state in air after stunning and until they remain unconscious when they leave the stun maintenance station. Both stations can be controlled from a microprocessor unit 4. The unit 4 controls the electrical field strength and frequency supplied to electrode 3. It can also control the speed of belt 7 which controls the length of time fish spend in station 6. Between the two stations unconscious fish pass over an inclined de-watering station 5.

Description

241 7408 - 1 - Fish Processing This invention concerns fish processing and

more particularly the slaughtering of fish.

It is estimated that worldwide less than 2 million of the approximately 80 million tonnes of fin-fish which are slaughtered annually are slaughtered humanely.

Devices have been proposed hitherto for stunning fish using electric currents prior to slaughter.

GB879314, for example, describes an electrical device which provides a series of short duration electrical pulses in water which stun fish in the water.

US5327854 describes a programmable device which generates output waveforms that will stun fish while minimising harm done to the fish.

The problem with such hitherto proposed devices is that some of the fish can regain consciousness if the stunning is inadequate, whilst the quality of the fish can be impaired if the stunning is excessive. - 2

According to the present invention there is provided a device for electrically slaughtering fish which comprises a stunning station for stunning the fish using an electric current, and a stun maintenance station which uses an electric current to maintain the fish in an unconscious state in air after stunning and until they remain unconscious when they leave the stun maintenance station.

The use of an electric current in air to maintain fish in a stunned state can reduce or indeed even eliminate the need for human intervention in the slaughtering of fish, and it can as a result contribute to a reduction in injuries which are often associated with such work. Furthermore, because the fish are held in a stunned state in air, the amount of electricity required to maintain the fish in an unconscious state after an initial stunning is generally low, particularly when compared with doing so in water.

The applied maintenance field will in general be from an alternating current source, for example at a low frequency which is readily available from the national grid, e.g. at 50Hz or 60Hz, or from higher frequency sources. A source of higher frequency electricity, for example of 500Hz or more, might be available, for example from the supply for the stun field used initially to stun the fish in the stunning station. The use of such higher frequencies can enable fish to be held in the maintenance field for extended periods, for example 28 seconds or more, e.g. 50 seconds or more, without substantial damage being imparted to the fish carcasses. In addition, the risk of electrical shock to operators of the apparatus can be minimised or even eliminated.

Typically, fields of from 10 to 20V AC can be used in the stun maintenance station. At 50Hz, lOV AC in the stun maintenance field could produce a reaction in humans if they were to put their hands into the field. However, 20V AC at 1,OOOHz this - 3 - effect is generally much reduced or even eliminated. This means that by suitably adjusting the electric field in the maintenance station, operators can reach into it with the maintenance field still applied and perform operations on fish outside it, such as cutting their gills, and without compromising the humane method, before returning the fish to the maintenance station.

The present invention also has the advantage that it can be made to work in both fresh and salt water environments.

Embodiments of devices in accordance with the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a schematic side view of a first embodiment; Fig. 2 is a schematic side view of a second embodiment; and Fig. 3 is a schematic perspective view of a mechanism which can be used with the embodiments of Figs. 1 and 2.

The device shown in Fig. 1, which is particularly designed for processing round fish, employs a two stage stunning process in which in a first stage the fish are initially rendered substantially instantly unconscious and in a second stage are then held unconscious until they are dead or are beyond recovery.

The first stage consists of a cylindrical plastics stun tube 1 of 1 to 2 metres in length and of a diameter sufficient to transport fish safely at a desired harvest rate. The tube 1, which has its cylindrical axis substantially horizontal, has three annular electrodes, two earth electrodes 2, 2' and a stun electrode 3 disposed between the two earth electrodes.

An electronics unit 4 underneath the tube 1 provides electrical signals to the electrode 3 required to stun the fish, these signals being microprocessor controlled. The microprocessor - 4 also provides feedback to an operator enabling the device to be operated safely and effectively. Furthermore, the microprocessor can be used to effect dynamic modification of the electrical field strength and its frequency supplied to the electrode 3, for example with changes in the species of fish being processed, their size, the number of fish in the tube, and the conductivity of the water in the tube. This can enable substantially all of the fish to be correctly stunned without blood-spotting, and without mechanical damage or haemorrhaging.

The microprocessor also enables continuous monitoring of the electric field and its frequency supplied to the electrode 3 so that stunning can be substantially optimised.

Typically the electric field will be generated by a class D amplifier having a specific resonating frequency resulting from a selected combination of capacitors and inductors at the output stage of a multitap transformer.

The unit 4 preferably stores algorithms which can be used to program the microprocessor according to the specific species, size and habitat of the fish being processed.

Unconscious fish leaving the stun tube 1 pass over an inclined dewatering section 5 and on to a maintenance station 6 which consists of an electrically earthed conveyor belt 7 and several electrically conductive curtains 8 hanging from above and over the conveyor belt 7.

The positioning of the curtains 8 over the belt 7 is adjusted according to the size of the fish being processed so that the fish passing along the belt 7 provide a continuous electrical connection between the curtains 8 and the belt 7. A rubber flap (not shown) near the entrance to the maintenance station 6 serves to even out the fish and prevent them lying on top of each other. - s -

The length of time the fish spend within the maintenance station 6 can be controlled by controlling the speed of the belt 7, and the latter can be controlled by the microprocessor in the unit 4. Since the fish are held in the maintenance tray in air, they will generally be in an irrecoverable state or dead when they leave the belt 7.

The maintenance station 6 can be configured in a number of ways to suit the size of fish, the speed of harvest, and the physical constraints of the location of the unit itself. Typically it would be 1 metre wide and 2 metres long, the fish being held on the belt for some 60 seconds.

Fish leaving the maintenance station 6 then pass down a chute 9 into harvest bins 10.

The device shown in Fig. 1 can be modified to make it more suitable for processing of flat rather than round fish.

In this case the substantially cylindrical stun tube 1 of Fig. 1 is replaced by a substantially rectangular section tube with the three electrodes being in the form of flat plates rather than annular rings, two of the plates being embedded in the roof of the tube 1 and being connected to a source of electrical power to effect stunning of the fish, with the third being embedded in the floor of the tube 1 being connected to earth.

As with the device shown in Fig. 1, the size of the rectangular tube will in general be selected according to the species of fish being processed, and the electronics unit 4 will be controlled by software according to the size and species of the fish being processed.

The device shown in Fig. 1, and the above described modification thereof, is of particular use in processing farmed fish, where the species, habitat and size of the fish is generally closely defined. The same criteria can apply to wild fisheries which can target specific species through their gear, location and - 6 - sonar sensing, and in these cases the device shown in Fig. 1 and its modification can be used by wild fisheries. The range of species caught is therefore often quite narrow, and the appropriate program can be used to process the fish in the device shown in Fig. 1 can often be readily selected. However, it is also possible to sort the different species caught on a fishing boat and then to process them separately, for example according to size and/or shape, for example using the same or different devices such as shown in Fig. 1 or as described above in a modification thereof.

A further modification of the device shown in Fig. 1 is shown in Fig. 2. This modification is of particular use in processing a variety of species of fish, for example both round and flat species, and especially fish which have been caught in the wild and brought on to deck on a fishing boat.

In this modification, the stun tube 1 of Fig. 1 is replaced by an inclined stun tray 11 which receives fish under gravity from the deck 12 of a boat down a chute 13. Live electrodes 14 hanging above the tray 11, and more particularly towards but not in contact with its earthed floor, stun fish passing along the tray 11, the stunning being controlled by the electronics unit 4'. The power required to effect adequate stunning of fish brought onto deck will in general be less than that required for fish which are pumped in water to the device shown in Fig. 1 due their already being in air.

The stunned fish are then passed under gravity down a further chute 5' and into a maintenance station 6' substantially identical to that described with reference to Fig. 1. Fish leaving the maintenance station 6' are then fed onwardly down a chute 9' for further processing, for example sorting and packaging.

Another type of maintenance station is shown in Fig. 3, this usually being used in conjunction with a conveyor type station as shown in Figs. 1 and 2, and after the fish have already been - 7 - held on a conveyor type station. For example, the maintenance station shown in Fig. 3 can be used to maintain fish in a maintenance field after they have had their gills cut, thereby enabling high bleed-out to be achieved under humane conditions.

The maintenance station shown in Fig. 3 is in the form of a carousel consisting of a series of cups 11 attached to an endless chain 12 driven by sprockets 13. Within each of the cups 11, which are made of an electrically insulating material, is a pair of maintenance electrodes 14, 14' which apply a maintenance field to a head region 15 of the fish 16.

The cups 11, which are shaped to accept the species of fish 16 being processed, hold the fish head 15 down, and since the maintenance field is only applied to the head region 15 of the fish 16, they can be held for several minutes with the field applied and without damaging the fish carcass.

The cups 11 can be arranged to eject fish automatically from them, for example into harvest bins. - 8 -

Claims

Claims 1. A device for electrically slaughtering fish which comprises a

stunning station for stunning the fish using an electric current, and a stun maintenance station which uses an electric current to maintain the fish in an unconscious state in air after stunning and until they remain unconscious when they leave the stun maintenance station.
2. A device according to claim 1, wherein the stunning station comprises a tube of substantially circular cross section.
3. A device according to claim 1, wherein the stunning station comprises a tube of substantially rectangular cross section.
4. A device according to claim 1, wherein the stunning station comprises a plurality of electrically conductive curtains.
5. A device according to any of the preceding claims, wherein the stun maintenance station comprises electrically conductive curtains.
6. A device according to any of the preceding claims, wherein the stun maintenance station comprises a conveyor belt.
7. A device according to any of the preceding claims, wherein the stun maintenance station comprises means which apply an electrical stun maintaining field substantially only to the head of the fish.
8. A device according to any of the preceding claims, wherein the electric field in the stun maintenance station is applied for a period of at least 28 seconds.
9. A device according to any of the preceding claims, wherein the electric field in the stun maintenance station is of a frequency of at least 500Hz. - 9 -
10. A device according to any of the preceding claims, wherein the electric field in the stun maintenance station is of a frequency about lOOOHz.
11. A device according to any of the preceding claims, wherein the stunning and/or the stun maintenance are controlled using a microprocessor.
12. A device for electrically slaughtering fish, the device being substantially as herein described with reference to the accompanying drawings.