Apparatus and method for the humane stunning of aquatic animals

Abstract

An apparatus for the humane stunning of aquatic animals comprises a support (6, Fig. 1) e.g., a tray on a belt conveyor, for supporting an aquatic animal and a stunning station (10) within which the s

Description

FIELD OF THE INVENTION This invention relates to apparatus and method for the humane stunning of aquatic animals and in particular to an apparatus and method for the humane stunning of aquatic animals suitable for use in water of high electrical conductivity (i.e. sea water). BACKGROUND OF THE INVENTION Currently there are two main high volume methods for the humane slaughter of fish and other aquatic animals, namely: A. Dry or semi-dry electric stunners; B. Inline flow through stunners. Dry or semi-dry electric stunners use vertical swinging tags (electrodes) which transfer electricity to the body of a fish lying on a metallic conveyor, the conveyor acting as an electrical earth. The fish pass under a number of these tags receiving an electric shock each time a tag contacts the body of a fish. The latter shocks are needed to increase the time to recovery. A water mist is sometimes used to keep the body of the fish body moist, enhancing the transfer of electricity into the fish. The latter is known as a semi-dry stunner. After dry / semi-dry stunning the fish are subsequently killed using a method such as immersion in ice or bleeding. Dry and semi-dry stunners have the benefit of being compact. However, the point contact of the tags / electrodes on the body of a fish can cause burn mark on the skin and the repeated muscular contractions caused by the electric shocks can lead to blood spots in the fillets. Furthermore, the fish are out of water for a period before they are stunned, which has poor welfare considerations. In an inline flow through fish stunner, an electric field is applied to water in which the fish are present via submerged electrode pairs, typically in a pipe through which the fish pass. This provides the best welfare, prior to slaughter, because the fish are always in water and it is possible to ensure a proper stun within a one second target by utilising specific electrical waveforms. The stun may be maintained for a number of seconds to extend the time to recovery. On exiting such a flow through apparatus, the stunned fish may be killed by insertion into ice slurry, bleeding or even by extending the pipeline allowing the stun maintenance time extend to over 60 seconds. The main drawback with existing inline flow systems is the power requirement, which, while not a significant issue in fresh water (typically having a conductivity of 50 - 500uS), becomes an increasing issue in water having a conductivity around 1000us and presents an almost insurmountable, and costly problem with full strength warm sea water (with a conductivity of over 55,000uS). Even with no fish in a sea water flow through apparatus, a huge amount of energy is consumed maintaining the required electrical field due to the high electrical conductivity of the salty water. This is not economical or sustainable for a fish farm and leaves a large carbon footprint with a massive cost. High DC currents typically used for inline flow through stunners in brackish and sea water systems cause extremely rapid corrosion of even the best marine grade stainless steel materials. Metallic electrodes with a positive polarity need to be replaced regularly and the resulting iron oxides introduced into the water may be detrimental in recirculating aquaculture systems. Pumps and fittings may also suffer significant corrosion, leading to pitting and leaks. An object of the present invention is to provide an apparatus for the humane stunning of aquatic animals that avoids the problems of direct contact dry stunners while being suitable for use in water of high electrical conductivity (i.e. sea water). SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided an apparatus for the humane stunning of aquatic animals as claimed in claim 1. Preferably said at least one first water outlet is arranged to supply water onto a head end of the animal and said at least one second water outlet is arranged to supply water onto a tail end of the animal when the support on which the animal rests is positioned in the at least one stunning station. Preferably the or each support is formed from an electrically non-conductive material The or each support may be water pervious to allow water to drain from the support. In one embodiment said at least one support may be adapted to laterally traverse the at least one stunning station such that an aquatic animal resting on the at least one support moves through the at least one stunning station. A plurality of said stunning stations may be arranged in side by side relationship, said at least one support being arranged to traverse said plurality of stunning stations such that an animal carried thereon is moved consecutively through each stunning station in turn. In one embodiment a plurality of supports may be defined on a conveyor arranged to convey the supports, and any animals carried thereon, through said at least one stunning station. Said conveyor, which may comprise a belt conveyor, may be formed from a water pervious and electrically insulating material. Transversely extending spacers may be located on said conveyor to separate the supports from one another and to define side walls of the supports. In one embodiment a row of said stunning stations may be arranged along an upper region of said conveyor such that each support, and an aquatic animal located thereon, is moved consecutively through each stunning station in turn. The first water supply of said at least one stunning station may comprise a first electrically conductive pipe adapted to deliver water to said least one first water outlet, said second water supply comprising a second electrically conductive pipe adapted to deliver water to said at least one second water outlet, said power supply being electrically coupled to said first and second pipes. Said at least one first water outlet of said first water supply may comprise a respective upper outlet nozzle arranged to deliver water downwardly onto a first end of said at least one support when located in the at least one stunning station, said at least one second water outlet of said second water supply comprising a respective upper outlet nozzle arranged to deliver water downwardly onto a second end of said at least one support, opposite said first end, when located in the at least one stunning station. The first and second water outlets of said first and second water supplies may each further comprise a respective lower outlet nozzle arranged to deliver water upwardly towards the respective upper outlet nozzle. Each of said first and second water supplies of said at least one stunning station may include a respective sump for collecting water exiting the respective pipe and a pump for circulating water collected in the respective sump back into the respective pipe. The sumps of the first and second water supplies are preferably electrically isolated from one another. According to a further aspect of the present invention there is provided a method of stunning aquatic animals as claimed in claim 15. In one embodiment the support comprises a conveyor formed from a water pervious and electrically insulating material, spacers being located on said conveyor to define a row of separate side by side parallel supports thereon, said method comprising driving said conveyor to convey animals carried thereon through said at least one stunning station. In one embodiment the method may comprise driving said conveyor to traverse said supports and any animals located thereon past a series of stunning stations arranged in side by side relationship. BRIEF DESCRIPTION OF THE DRAWINGS An apparatus for the humane stunning of aquatic animals, in particular fish, in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figures 1 and 2 are perspective views of an apparatus for the humane stunning of aquatic animals in accordance with an embodiment of the present invention; Figure 3 is a plan view of the apparatus of Figures 1 and 2; Figure 4 is a side view of the apparatus of Figures 1 and 2; Figure 5 is a sectional view on line B-B of Figure 4; Figure 6 is a detailed perspective view of one stunning station of the apparatus of Figures 1 and 2; Figure 7 is a side view of the stunning station of Figure 6; and Figures 8a to 8c are perspective views of alternative nozzle designs for use with the stunning station of Figure 6. DETAILED DESCRIPTION OF THE DRAWINGS As illustrated in the drawings, an apparatus for the humane stunning of aquatic animals, in particular fish, in sea water in accordance with an embodiment of the present invention comprises an endless belt conveyor 2 formed from a water pervious and electrically insulating material and having transversely extending spacer bars 4 located thereon to define a row of separate side by side, parallel supports 6 thereon upon which supports 6 fish 1 may be placed, preferably in common head to tail alignment resting on the belt conveyor 2 and extending between adjacent pairs of spacer bars 4. While embodiments of the present invention have been described below in relation to the stunning of fish, it is envisaged that an apparatus and method in accordance with the present invention may be suitable for stunning numerous other aquatic animals. The belt conveyor 2 is driven by a suitable drive motor to convey fish 1 carried thereon through a row of stunning stations 10. Each stunning station 10 comprises at least one first water outlet adapted to deliver a first flow of water from a first water supply onto one end of a fish as it passes through the stunning station and at least one second water outlet adapted to deliver a second flow of water from a second water supply onto a second end of the fish, a power supply 12 being coupled to the first and second water supplies to generate a potential difference between said first flow of water and said second flow of water whereby an electrical circuit is completed when said first and second flows of water impinge upon the body of the fish such that an electrical current flows through the fish to stun it. Preferably the fish 1 are placed on the conveyor 2 such that said at least one first water outlet is arranged to supply water onto a head end of the fish and said at least one second water outlet is arranged to supply water onto a tail end of the fish when the support 6 on which the fish rests passes through a respective stunning station 10. In the embodiment shown in the drawings and as best illustrated in Figures 5 to 7, the first water supply of each stunning station comprises a first pipe 14a, at least a portion of which is electrically conductive, adapted to deliver water from a respective sump 16a, via a pump 18a, to said least one first water outlet. The second water supply comprises a second electrically conductive pipe 14b adapted to deliver water from a respective sump 16b, via a pump 18b, to said at least one second water outlet. The power supply 12 is electrically coupled to electrically conductive (e.g. metallic) portions of the first and second pipes 14a, 14b. In the embodiment shown, the first and second water supplies of each stunning station comprises a respective upper outlet nozzle 20a,20b arranged to deliver water downwardly towards the body of a fish 1 on the conveyor 2 as its support 6 passes through the respective stunning station 10, and a respective lower outlet nozzle 22a,22b arranged to deliver water upwardly towards the respective upper outlet nozzle 20a,20b. Figure 8a, 8b and 8c illustrate different types of outlet nozzles having single or multiple outlets and different arrangements of multiple outlets. The sumps 16a, 16b of the first and second water supplies are electrically isolated from one another. There must not be any conductive material connecting each half of each stunning station to avoid electrical current flowing between the sumps other via than the power supply connecting cables from the power supply to the electrically conductive portions of the pipes 14a, 14b. Means may be provided for controlling the level of water in each sump 16a,16b. To maintain the quality, level or constant head of pressure of the water in the sumps of each stunning station, water, preferably from the source containing the aquatic animal prior to them being delivered onto the conveyor 2, may be added to the sumps from time to time. Each sump preferably includes an over flow to carry away surplus water to maintain the level in the respective sump. The level in each sump can be maintained by balancing the in &out flows or via a level sensor controlling a small feed pump (not shown). How the electricity, in an in-line flow through apparatus, tank, or even when using electric fishing equipment enters the fish still remains an unanswered question. Whether it is absorbed cell wise throughout the body, through the fish’s lateral line or simply as a head to tail electric field voltage is still debated. In all three theories it is generally agreed that the electric field is distorted according to impedance miss match between the fish and the water. Maximum power transfer should take place when the impedance of the fish matches the impedance of the power unit and water combination i.e. when the electric field is not distorted. In dry stunning and semi-dry stunning, the electricity enters the fish body through a point on the head area and passes through to an area of contact on side of the fish, roughly in the middle of the body i.e. the area that rests on the conveyor acting as an electrical earth. Even in this configuration the fish are still able to be stunned effectively, (eeg recordings are available as proof). The present invention provides a compliant, humane method of stunning of aquatic animals, primarily fish, at all voltages using minimum electric power in water of high conductivity. The apparatus may operate with water having a conductivity between 20uS and 65,000uS and may be particularly suitable for use with sea water, although it may also be used with fresh water. Each pump 18a, 18b of each of the first and second water supplies may draw water from the respective sump 16a, 16b through a flexible non-metallic tube portion and through a respective metallic pipe 14a, 14b and into and through the respective upper and lower outlet nozzles 20a,20b,22a,22b facing one another, preferably one above the other. A non-metallic drip tray 24, preferably with a central divider 26, may be provided beneath the conveyor 2, adjacent the stunning stations 10, to catch any splashes of water which might not fall back into a sumps when fish 1 pass between the outlet nozzles of the stunning stations 10 upon the supports 6 defined by the conveyor 2. The purpose of the divider 26 may be to minimise water contact between the two halves of each stunning station 10, minimising leakage current. Each side of the drip tray 24 may have its own drain 28 (see Figure 7). Feed and overflow tubes of the sumps and drip tray drains should be of sufficient length, and be made of non-conductive materials and narrow bore, to increase the resistance of the water columns contained within them. The purpose of the length is to reduce the leakage current and make the apparatus more electrically efficient. The approximate resistance of the columns of water from the upper and lower outlet nozzles can be calculated using the formula R=pl / a where R is the columnar resistance in Ohms, p is the specific resistance of the water in ohms per cc and a is the tube internal cross sectional area in centimetres. The specific resistance of the water in Ohms is 1 / the conductivity of the water. Those trained in the art will understand that these columns of water, of sufficient length are necessary to reduce leakage current between the two halves of the station. However the raw water entrance of the inlet and exit of all outflow columnar tubes from each station, should be electrically inter-connected to eliminate leakage voltages between them. This can be achieved by passing the water columns through an electrically conductive manifold connecting the columns. This may be particularly important for safety if it is proposed to use the apparatus with very high voltages. Any number of stunning stations 10 may be cascaded to accommodate the user’s existing or proposed power supplies. For example, one embodiment may have a first stunning station followed by one or more stun maintenance stations. Another embodiment of the apparatus may consist of an anaesthesia station followed by a stunning station and further stun maintenance stations. A further embodiment of the apparatus using ultra high voltage pulses may require just a solitary stunning station. According to the size of the fish or other aquatic animals, and the rate of stunned aquatic animals required per minute, the dimensions of the or each stunning station and, style of outlet nozzle and the length or size can be established. The horizontal distance between the outlet nozzles at either end of each stunning station may be a particular dimension of any aquatic animal, in fish preferably a distance between the head and tail. The vertical distance (D, Figure 7) between the upper and lower outlet nozzles is preferably set to allow the aquatic animal to pass between the nozzles with sufficient clearances so as not to touch the nozzles. According to the size offish, a nozzle arrangement can be utilised to obtain the best results. In one embodiment only one nozzle pair in each stunning station may be required. In a further embodiment a pair of in-line of nozzles may be fed from the same pipe and could be used for a larger fish or other aquatic animals. The number of nozzles in any configuration may range from 1 to n. In a third embodiment a circular arrangement nozzles many be employed. It is possible, in other embodiments to use any other nozzle arrangements. The total internal cross sectional areas of these multiple nozzle arrangements should be designed to approximate to the internal cross sectional area of the respective supply pipe 14a, 14b. In one embodiment, a number of power supplies and water supply pipes, pumps and nozzles types may be associated with the sumps in any one or more stations. Those experienced in the art will know how to connect these power supplies with various voltages and waveforms into configurations to produce the required response. Examples might be but not exclusively a voltage ramp up or down to avoid myoclonic muscular jerks, or morphing from one waveform to another. The belt conveyor 2 may run continually or on a cyclic programme or a combination of both. In an embodiment where the belt conveyor 2 is running continually, the fish may pass steadily between the outlet nozzles of each stunning station. Dependant on the conveyor speed and the species and size of fish it may be necessary to use more than one upper and lower outlet nozzle in each stunning station to keep the aquatic animal in the electric field for the length of time required to obtain the required response In an embodiment where a cyclic motion of the belt conveyor 2 may be used, the movement of the belt 2 may be arranged such that each aquatic animal located in the belt 2 will be stationary under the outlet nozzles of each stunning station 10 for a predetermined dwell time before moving rapidly to the next station. The apparatus may be at least partially enclosed within a housing, preferably formed from a transparent material, to provide mechanical and electrical safety to protect the operator while allowing the operator to observe the reactions of the aquatic animals being processed. This observation may be required to ensure that the apparatus is working as designed. 5 The invention is not limited to the embodiments described herein but can be amended or modified without departing from the scope of the present invention.

Claims

1. An apparatus for the humane stunning of aquatic animals comprising at least one support for supporting an aquatic animal thereon, at least one stunning station within which the at least one support is located or through which the at least one support is adapted to traverse, said at least one stunning station comprising at least one first water outlet adapted to deliver a first flow of water from a first water supply onto a first region of an animal resting upon said at least one support and at least one second water outlet adapted to deliver a second flow of water from a second water supply onto a second region of said animal, distal from said first region thereof, a power supply being coupled to the first and second water supplies to generate a potential difference between said first flow of water and said second flow of water, whereby an electrical circuit is completed when said first and second flows of water impinge upon the body of an animal such that an electrical current flows through the animal to stun the animal, wherein said at least one support defines a trough or tray upon which an aquatic animal may rest.

2. An apparatus as claimed in claim 1, wherein said at least one first water outlet is arranged to supply water onto a head end of the animal and said at least one second water outlet is arranged to supply water onto a tail end of the animal when the support on which the animal rests is positioned in the at least one stunning station.

3. An apparatus as claimed in any preceding claim, wherein said at least one support is formed from an electrically non-conductive material4. An apparatus as claimed in any preceding claim, wherein said at least one support is water pervious to allow water to drain from the support.

5. An apparatus as claimed in any preceding claim, wherein said at least one support is adapted to laterally traverse the at least one stunning station such that an aquatic animal resting on the at least one support moves through the at least one stunning station.

6. An apparatus as claimed in claim 5, wherein a plurality of said stunning stations are arranged in side by side relationship, said at least one support being arranged to traverse said plurality of stunning stations such that an animal carried thereon is moved consecutively through each stunning station in turn.

7. An apparatus as claimed in claim 5 or claim 6, wherein a plurality of supports are defined on a conveyor arranged to convey the supports, and any animals carried thereon, through said at least one stunning station.

8. An apparatus as claimed in claim 7, wherein said conveyor is formed from a water pervious and electrically insulating material9. An apparatus as claimed in claim 8, wherein transversely extending spacers are located on said conveyor to separate the supports from one another and to define side walls of the supports.

10. An apparatus as claimed in any of claims 7 to 9, wherein a row of said stunning stations are arranged along an upper region of said conveyor such that each support, and an aquatic animal located thereon, is moved consecutively through each stunning station in turn.

11. An apparatus as claimed in any preceding claim, wherein said first water supply of said at least one stunning station comprises a first electrically conductive pipe adapted to deliver water to said least one first water outlet, said second water supply comprising a second electrically conductive pipe adapted to deliver water to said at least one second water outlet, said power supply being electrically coupled to said first and second pipes.

12. An apparatus as claimed in claim 11, wherein said at least one first water outlet of said first water supply comprises a respective upper outlet nozzle arranged to deliver water downwardly onto a first end of said at least one support when located in the at least one stunning station, said at least one second water outlet of said second water supply comprising a respective upper outlet nozzle arranged todeliver water downwardly onto a second end of said at least one support, opposite said first end, when located in the at least one stunning station.

13. An apparatus as claimed in claim 12, wherein the first and second water outlets of said first and second water supplies each further comprise a respective lower outlet nozzle arranged to deliver water upwardly towards the respective upper outlet nozzle.

14. An apparatus as claimed in any of claims 11 to 13, wherein each of said first and second water supplies of said at least one stunning station includes a respective sump for collecting water exiting the respective pipe and a pump for circulating water collected in the respective sump back into the respective pipe.

15. An apparatus as claimed in claim 14, wherein the sumps of the first and second water supplies are electrically isolated from one another.

16. A method of stunning aquatic animals comprising the steps of locating an aquatic animal on a support defining a trough or tray upon which an aquatic animal may rest, locating said support in or traversing said support through at least one stunning station, when said at least one support is in said at least one stunning station, delivering a first flow of water onto a first region of the animal from a first water supply via at least one first water outlet, delivering a second flow of water from a second water supply onto a second region of the animal from at least one second water outlet, and supplying electrical power to said first and second water supplies whereby an electrical circuit is completed by the body of the aquatic animal such that an electrical current flows through the animal to stun the animal.

17. A method as claimed in claim 16, wherein the support is formed from an electrically non-conductive material.

18. A method as claimed in claim 16 or claim 17, wherein the support comprises a conveyor formed from a water pervious and electrically insulating material, spacers being located on said conveyor to define a row of separate side by side parallelCMCM CMsupports thereon, said method comprising driving said conveyor to convey animals carried thereon through said at least one stunning station.

19. A method as claimed in claim 18, wherein said method comprises driving said 5 conveyor to traverse said supports and any animals located thereon past a series of stunning stations arranged in side by side relationship.

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