Improved fish stunner

Abstract

An apparatus and method for stunning fish, the fish stunner has a conveyor along which live fish are transportable along the length of a conduit in a first direction of travel. An electrical circuit is provided with a first electrode, a second electrodes and a conducting fluid which is extendable between the first and second electrodes to complete the electrical circuit. The conducting fluid flows from the first electrode to the second electrode, such that, when a voltage is applied across the first and second electrode, the conducting fluid may apply a shock to stun a fish in the path of the conducting fluid.

Description

[0001] Improved Fish Stunner

[0002] Field of Invention

[0003] The present invention relates an apparatus and method for fish stunning apparatus and method suitable for use in fish or other animal stunning, particularly for example, saltwater fish stunning.

[0004] Background of the Invention

[0005] Fish farming is a type of aquaculture, which is the controlled cultivation and harvesting of aquatic animals such as fish, crustaceans, molluscs and so on, in natural or pseudo-natural environments.

[0006] Global demand for dietary fish protein has increased, which has resulted in widespread overfishing in wild fisheries, resulting in significant decrease in fish stocks and even complete depletion in some regions. Fish farming allows establishment of artificial fish colonies that are provided with sufficient feeding, protection from natural predators and competitive threats, access to veterinarian service, and easier harvesting.

[0007] Humane slaughter techniques on land based farms have outpaced developments in aquaculture processing. Inhumane practices include, for example the use of CC and dropping live fish (principally seabass, bream, tilapia and salmon smolts) into tubs of ice where it can take an unacceptable duration for the fish to be killed.

[0008] Mechanised percussive machines have been used to kill larger fish, such as salmon and seatrout, however they do not cater for portion sized fish. Many animal welfare organisations do not explicitly endorse the use of electrical stunning because in the past it has been done very poorly and systems capable of humane stunning are relatively new.

[0009] The present applicant, Ace Aquatec Ltd, has previously made and sold a flow- through fish stunner designed for low power fresh water use with a first stage (stun station) in which 1 m long electrodes on opposing sides of the tube were provided with 1 000HZ AC voltage to deliver around 3- 11 V / cm transversely across the tube (depending on the current measured) and a second stun maintenance stage of around 16-18m comprising seven or more pairs of electrodes 2m long on opposing sides of the tube powered with a 50 Hz AC voltage to provide the required electric field.

[0010] A later recirculating fish stunner reduced the power demands by reducing the volume of water to be electrified and by using recirculating water and controlling the salinity, and hence conductivity, to be close to that of fresh water. Fish, including saltwater fish species, could then be stunned humanely within one second but in a fixed slow moving volume of lower conductivity water. This system works well but required regular cleaning of the system, regular water exchange, and additional fish handling to deliver these into the recirculating water supply.

[0011] PCT / GB2015 / 052809 describes a flow-through fish stunner for use in saltwater flow- through fish stunning. The device has an elongate stunner tube configured so that water can flow-through the tube in a flowthrough manner, at least three stunning electrodes spaced along the stunner tube configured to provide an electric field substantially longitudinally along the stunner tube a high power alternating voltage power supply which supplies Ov to at least one stunning electrode and a high power alternating voltage to at least one remaining stunning electrodes.

[0012] Summary of the Invention

[0013] It is an object of the present invention to provide an improved fish stunner.

[0014] In accordance with a first aspect of the invention there is provided, an apparatus for stunning fish, the apparatus comprising: a conveyor along which live fish are transportable along the length of a conduit in a first direction of travel; an electrical circuit comprising: a first electrode, a second electrode and a conducting fluid which is extendable between the first and second electrodes in one or more streams to complete the electrical circuit, wherein (e.g. in use) the conducting fluid flows from the first electrode to the second electrode, such that, when a voltage is applied across the first and second electrode, the conducting fluid may apply a shock to stun a fish in the path of the conducting fluid.

[0015] Alternatively, the electrical circuit comprises: a first electrode and a second electrode, wherein a conducting fluid is extendable between the first and second electrodes in one or more streams to complete the electrical circuit.

[0016] Preferably, one or more streams of conducting fluid are configured to flow between the first and second electrodes with a restricted width, such that the current is provided in the conduit in a well-defined area along its length. For example, the width of the one or more streams of conducting fluid is measured in the same direction as the length of the conduit.

[0017] Preferably, the or each stream (or the or each fluid flow) has a width of less than 5 cm, more preferably of less than 4 cm, still more preferably of less than 3 cm, for example of less than 2 cm.

[0018] Preferably, the stream has a width of more than 0.5 cm, more preferably of more than 1 cm, still more preferably of more than 1 .5 cm, for example of more than 2 cm.

[0019] Preferably, the electrical circuit is positioned such that the conducting fluid flows in a direction across the first direction of travel.

[0020] Preferably, the electrical circuit is positioned such that the conducting fluid flows in a direction substantially orthogonal to the first direction of travel.

[0021] For example, the electrical circuit is positioned such that the conducting fluid flows in a downward direction (e.g. under gravity) across the first direction of travel. In one option, the electrical circuit is positioned such that the conducting fluid flows (e.g. at least in part) in a waterfall or waterfall-like manner. Preferably, the apparatus further comprises a fluid inlet positioned at or near or proximal to the first or second electrode. For example, the apparatus is configured such that conducting fluid that flows from the fluid inlet contacts the first or second electrode, e.g. before or prior to reaching the conveyor (or fish to be stunned).

[0022] Preferably, the apparatus further comprises a fluid outlet positioned remote from (and, optionally, generally opposite to) the fluid inlet to receive fluid which has flowed from the first to the second electrode.

[0023] Optionally, the one or more streams of conducting fluid may be jets of fluid and / or sheets of fluid.

[0024] Preferably, the fluid inlet creates a jet or stream or sheet of fluid which is extendable between the first and second electrodes.

[0025] Preferably, the apparatus comprises a plurality of fluid inlets each of which create a jet or stream or sheet of fluid.

[0026] Preferably, a set of fluid inlets are arranged in a plane substantially orthogonal or substantially parallel to the first direction of travel.

[0027] Preferably, a plurality of sets of fluid inlets are spaced along the length of the conduit.

[0028] Preferably, a controller is provided to selectively switch on (and off) one or more electrical circuit and, optionally, fluid inlet (e.g. the corresponding fluid inlet).

[0029] Preferably, a camera is provided to detect the position of fish within the conduit.

[0030] Preferably, the camera is connected to the controller such that the electrical circuit and (e.g. corresponding) fluid inlet may be switched on (and off) in response to information on the detected position of the fish. Alternatively, the fluid inlet creates a sheet (or sheets) of fluid which is extendable between the first and second electrodes across the first direction of travel.

[0031] Preferably, the sheet of fluid extends substantially over (or substantially occludes) the cross sectional area of the conduit.

[0032] Preferably, the fluid outlet provides a recirculation path to the fluid inlet.

[0033] Preferably, the apparatus comprises: a fluid inlet positioned at or proximal to or near the first or second electrode; a fluid outlet positioned remote from the fluid inlet to receive fluid which has flowed from the first to the second electrode; and a recirculation path (e.g. a recirculation path means) for recirculating fluid received by the fluid outlet back to the fluid inlet (e.g. for re-use). The fluid inlet and / or the fluid outlet may be as further defined above.

[0034] Preferably, the recirculation path (or recirculation path means) comprises a pump means for recirculating the fluid. Optionally, the recirculation path (or recirculation path means) comprises a filtration means (e.g. including grates, grids, grills, sieves and / or other filters), e.g. for filtering the conducting fluid before re-use.

[0035] Optionally, the conveyor comprises rollers. Optionally, the conveyor is a gravity feed. Optionally, the conveyor is a liquid stream.

[0036] In a preferred option, the conveyor is configured for transporting the live fish along the length of the conduit out of water. In this case, for example, where the conducting fluid is a conducting liquid, the fish will only come into contact with a liquid when in a path of conducting liquid. Preferably, the apparatus further comprises a dewatering station upstream of the conveyor. Preferably, in this option, the conveyor does not use a liquid (e.g. water), e.g. a flow of liquid, for transporting fish in the first direction of travel.

[0037] In a further preferred option, the conveyor is a liquid stream. For example, the live fish are transported along the length of the conduit in a flow of liquid (e.g. in water, such as seawater or brackish water). Preferably, the first electrode is configured to form an electrical circuit with the second electrode (e.g. through or via the liquid stream) without directly (or physically) contacting the fish. For example, the first electrode may be disposed on or define at least a portion of an inner surface of the conduit.

[0038] Preferably, the second electrode is configured to directly (or physically) contact the fish as they are transported (or pass) through the conduit in the liquid stream. Preferably, in use, the second electrode is configured to be at least partially (or fully) submerged in the liquid stream. For example, the second electrode may comprise one or more conductive elements / members (e.g. metal plates or chains) that hang down (or dangle) in the conduit. In another example, the second electrode may comprise a surface or slide that, in use, is disposed / submerged within the liquid stream and along which the fish travel (or generally slide against) while remaining in the liquid stream. For example, the slide may be a continuous and / or non-flexible conductive surface. In another example, the slide may be a resilient and / or flexible conductive surface, e.g. by comprising a plurality of chains (e.g. arranged lengthwise with respect to the conduit) or chainmail. At least a portion of (or at least one region of) the length of the conduit may comprise the first electrode and / or the second electrode.

[0039] Preferably, the fluid is a conducting liquid. Optionally, the conducting liquid is sea water. Preferably, the conducting liquid is brackish water.

[0040] In accordance with a second aspect of the invention there is provided a method for stunning fish, the method comprising: transporting a live fish along the length of a conduit in a first direction of travel through a region of the conduit which contains an electrical circuit, the electrical circuit comprising: a first electrode, a second electrode and a conducting fluid which is extendable between the first and second electrodes in one or more streams to complete the electrical circuit wherein (e.g. in use) the conducting fluid flows from the first electrode to the second electrode, such that, when a voltage is applied across the first and second electrode, the conducting fluid may apply a shock to stun a fish in the path of the conducting fluid. Alternatively, the electrical circuit comprises: a first electrode and a second electrode, wherein a conducting fluid is extendable between the first and second electrodes in one or more streams to complete the electrical circuit.

[0041] Preferably, one or more streams of conducting fluid are configured to flow between the first and second electrodes with a restricted width, such that the current is provided in the conduit in a well-defined area along its length. For example, the width of the one or more streams of conducting fluid is measured in the same direction as the length of the conduit.

[0042] Preferably, the or each stream (or the or each fluid flow) has a width of less than 5 cm, more preferably of less than 4 cm, still more preferably of less than 3 cm, for example of less than 2 cm.

[0043] Preferably, the stream has a width of more than 0.5 cm, more preferably of more than 1 cm, still more preferably of more than 1 .5 cm, for example of more than 2 cm. Preferably, the electrical circuit is positioned such that the conducting fluid flows in a direction across the first direction of travel.

[0044] Preferably, the electrical circuit is positioned such that the conducting fluid flows in a direction substantially orthogonal to the first direction of travel.

[0045] Preferably, the method further comprises introducing the conducting fluid via a fluid inlet positioned at or near or proximal to the first or second electrode.

[0046] Preferably, the method further comprises removing the conducting fluid from the conduit via a fluid outlet positioned remote from (and, optionally, generally opposite to) the fluid inlet to receive fluid which has flowed from the first to the second electrode.

[0047] Optionally, the one or more streams of conducting fluid may be jets of fluid and / or sheets of fluid.

[0048] Preferably, the fluid inlet creates a jet or stream or sheet of fluid which is extendable between the first and second electrodes. Preferably, the method comprises using a plurality of fluid inlets each of which create a jet or stream or sheet of fluid.

[0049] Preferably, a set of inlets are arranged in a plane substantially orthogonal or substantially parallel to the first direction of travel.

[0050] Preferably, a plurality of sets of fluid inlets are spaced along the length of the conduit.

[0051] Preferably, the one or more electrical circuit and (e.g. corresponding) inlet are selectively switched on (and off).

[0052] Preferably, a position of fish within the conduit is detectable using a camera.

[0053] Preferably, the camera is connected to a controller such that the electrical circuit and (e.g. corresponding) inlet may be switched on (and optionally off) in response to information on the detected position of the fish.

[0054] Alternatively, the conducting fluid comprises a sheet of fluid which is extendable between the first and second electrodes across the first direction of travel.

[0055] Preferably, the sheet of fluid extends substantially over (or substantially occludes) the cross sectional area of the conduit.

[0056] Preferably, the fluid outlet provides a recirculation path to the fluid inlet.

[0057] Preferably, the method comprises recirculating the conducting fluid from a fluid outlet to a fluid inlet, e.g. wherein the fluid outlet is positioned remote from a fluid inlet and / or wherein the fluid outlet is configured to receive fluid which has flowed from the first to the second electrode.

[0058] Optionally, the fish are transported on a conveyor which comprises a plurality of rollers. Optionally, the fish are transported on a conveyor which comprises a gravity feed.

[0059] Optionally, the fish are transported on a conveyor which comprises a liquid stream.

[0060] Preferably, the fluid is a conducting liquid

[0061] Optionally, the conducting liquid is sea water.

[0062] Preferably, the conducting liquid is brackish water.

[0063] Where the context allows, any features of the first aspect may be incorporated into the second aspect (and vice versa).

[0064] Brief Description of the Drawings

[0065] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which:

[0066] Figure 1 is a schematic drawing of a first example of an apparatus in accordance with the present invention;

[0067] Figure 2 is a cross section of a conduit which shows an example of a conducting fluid in accordance with the present invention;

[0068] Figure 3 is a cross section of a conduit which shows an example of a conducting fluid in accordance with the present invention;

[0069] Figure 4 is a flow diagram which shows an example of a method in accordance with the present invention;

[0070] Figures 5a to 5c is a schematic diagram which shows a second embodiment of an apparatus in accordance with the present invention; Figure 6 is a perspective view of a third embodiment of an apparatus in accordance with the present invention; and

[0071] Figure 7 is a schematic diagram which shows a fourth embodiment of an apparatus in accordance with the present invention.

[0072] Detailed Description of the Drawings

[0073] The following embodiments of the present invention show a fish stunner which has been designed to humanely and efficiently stun fish, particularly farmed fish such as salmon. In this and other examples, the fish is conveyed along a conduit in a first direction of travel and the fish is stunned by an electrical signal which is provided by an electrical circuit which is, in part, formed from a conducting fluid coupled to a positive and a negative electrode. Conveniently, the conducting fluid is water such as sea water or brackish water.

[0074] Advantageously, the conducting fluid extends over the cross section of the conduit along which the fish is conveyed and the electric shock is applied when the fish passes through the conducting fluid. Accordingly, one or more streas of conducting fluid are configured to flow between the first and second electrodes with a restricted width, such that the current is provided in the conduit in a well-defined area along its length. For example, the width of the flow may be between 3cm and 5 cm. In this and other embodiments of the present invention, example, the purpose is to limit length along the conduit over which the current is applied.

[0075] Figure 1 is a schematic drawing of a first example of an apparatus in accordance with the present invention. Figure 1 shows a stunner 1 which comprises a conduit 3 through which fish 15 are conveyed in a first direction 5. The fish may be conveyed by any suitable means. A circuit 7 is connected across the conduit 3, the circuit 7 comprises first electrode 9 arranged at a first side of the conduit and a second electrode 11 at a second side of the conduit. The space between the first electrode 9 and the second electrode 11 is, in use, at least partially occupied by a conducting fluid 13 which forms part of the electrical circuit by providing a conduction path between the first electrode and the second electrode. Figure 2 is a cross section of a conduit which shows an example of a conducting fluid in accordance with the present invention.

[0076] In this example, the conduit cross section 21 shows a fluid inlet 23, a fluid outlet 25 and a sheet of fluid 27. The inlet and outlet are designed to allow the conducting fluid to cover substantially the entire cross sectional area of the conduit 21 . In this embodiment, an electric shock will be experienced by a fish crossing through the sheet of conducting fluid 27. Advantageously, this maximises the ability to ensure that each fish will be stunned when it goes through the conduit.

[0077] Figure 3 is a cross section of a conduit which shows an example of a conducting fluid in accordance with the present invention.

[0078] In this example, the conduit cross section 31 shows a fluid inlet 33, a fluid outlet 35 and a plurality of jets of conducing fluid 37. The inlets and outlets are designed to allow the conducting fluid to go between the inlets 33 and respective outlets 35. In this example, coverage of the cross section is partial and gaps arise between the jets. However, careful selection of the position of the jets ensures that an electric shock will be experienced by a fish crossing through the cross section occupied by the jets. In addition, the jets may be more electrically efficient.

[0079] Figure 4 is a flow diagram which shows an example of a method in accordance with the present invention.

[0080] The method 41 comprises transporting a live fish along the length of a conduit 43. The fish enters a region of the conduit which contains an electrical circuit comprising electrodes and a conducting fluid 45. A voltage is applied across the first and second electrode, such the conducting fluid may apply a shock to stun a fish in the path of the conducting fluid.

[0081] Figures 5a to 5c is a schematic diagram which shows a second embodiment of an apparatus in accordance with the present invention. The figures show a stunner 51 which has a conduit 53. In this example, the conduit has a rectangular cross section. Fish 65 are transported in a first direction 55 along the conduit toward a circuit 57. Circuit 57 comprises a first electrode 59, a second electrode 61 and a conducting fluid 63 which forms a conducting pathway of the circuit in the conduit 53.

[0082] In this example, the fish 65 are conveyed through the conduit on rollers 67. Tank 69 is positioned below the conduit to collect conducting fluid, which in this example is an ionic solution, typically salt water or brackish water. Cameras 71 are provided to locate the position of the fish as they are conveyed.

[0083] Figure 5a shows a single use of conducting fluid 63 to complete a circuit with electrodes 59, 61 . Fig. 5c shows an array of inlets 75 through which jets of conducting fluid may be provided across the cavity between positive and negative electrodes.

[0084] The control system 73 controls the power supply to the circuits, controls the switching on and off of jets of conducting fluid and receives data from the cameras on the position of the fish. This information may be used to selectively switch on circuits to target the provision of the electric current in the cavity.

[0085] Figure 6 is a perspective view of a third embodiment of an apparatus in accordance with the present invention. Fig.6 shows a stunner 81 , conduit 83 a first direction 85 in which the fish 93 travel into the conduit 83. A first electrode 89, second electrode 91 , tank 95 and rollers 97. This embodiment is similar to that of figures 5a to 5c, but with fewer inlets 99.

[0086] Figure 7 is a schematic diagram which shows a fourth embodiment of an apparatus in accordance with the present invention. Figure 7 shows a stunner 101 which comprises a conduit 103. The direction of travel 105 of the fish 115 being conveyed into the conduit 103. In some embodiments, the conduit may be at an angle to the horizontal with the entrance above the exit such that gravity acts to move the fish through the conduit.

[0087] The circuit 107 comprises a first electrode 109, a second electrode 111 and a conducting fluid 113 which forms the conducting path through the conduit between the first and second electrodes 109, 111. In this example of the present invention, the conducting fluid is provided to the conduit by inlets 117 which allow the formation of a sheet or plane of conducting fluid which extends substantially entirely over the cross section of the conduit. Fluid outlets 119 and a fluid return path 121 recirculate the conducting fluid to the inlet for re-use.

[0088] In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

[0089] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims

Claims1 . An apparatus for stunning fish comprising: a conveyor along which live fish are transportable along the length of a conduit in a first direction of travel; an electrical circuit comprising: a first electrode, a second electrode and a conducting fluid which is extendable between the first and second electrodes in one or more streams to complete the electrical circuit, wherein the conducting fluid flows from the first electrode to the second electrode, such that, when a voltage is applied across the first and second electrode, the conducting fluid may apply a shock to stun a fish in the path of the conducting fluid.

2. The apparatus as claimed in claim 1 wherein, the one or more streams are configured to flow in one or more stream between the first and second electrodes with a restricted width, such that the current is provided in the conduit in a well- defined area along its length.

3. The apparatus as claimed in claim 1 or claim 2 wherein, the or each stream has a width of less than 5 cm.

4. The apparatus as claimed in claim 1 or claim 2 wherein, the or each stream has a width of less than 3 cm.

5. The apparatus as claimed in any one of the preceding claims wherein, the electrical circuit is positioned such that the conducting fluid flows in a direction across the first direction of travel.

6. The apparatus as claimed in any one of the preceding claims wherein, the electrical circuit is positioned such that the conducting fluid flows in a direction substantially orthogonal to the first direction of travel.

7. The apparatus as claimed in claim 5 or claim 6 wherein, the electrical circuit is positioned such that the conducting fluid flows in a downward direction under gravity.

8. The apparatus as claimed in any one of the preceding claims which further comprises a fluid inlet positioned at or proximal to the first or second electrode.

9. The apparatus as claimed in any one of the preceding claims which further comprises a fluid outlet positioned remote from the fluid inlet to receive fluid which has flowed from the first to the second electrode.

10. The apparatus as claimed in claim 8 or claim 9 wherein, the fluid inlet creates a jet or stream or sheet of fluid which is extendable between the first and second electrodes.11 . The apparatus as claimed in any one of claims 8 to 10 comprising a plurality of fluid inlets each of which create a jet or stream or sheet of fluid.

12. The apparatus as claimed in any one of claims 8 to 11 wherein, a set of fluid inlets are arranged in a plane substantially parallel to the first direction of travel.

13. The apparatus as claimed in any one of claims 8 to 12 wherein, a plurality of sets of fluid inlets are spaced along the length of the conduit.

14. The apparatus as claimed in any one of the preceding claims wherein, a controller is provided to selectively switch on one or more electrical circuit and fluid inlet.

15. The apparatus as claimed in any one of the preceding claims wherein, a camera is provided to detect the position of fish within the conduit.

16. The apparatus as claimed in claim 15 wherein, the camera is connected to the controller such that the electrical circuit and fluid inlet may be switched on in response to information on the detected position of the fish.

17. The apparatus as claimed in claim 8 wherein the fluid inlet creates a sheet of fluid which is extendable between the first and second electrodes across the first direction of travel.

18. The apparatus as claimed in claim 17 wherein, the sheet of fluid extends substantially over the cross sectional area of the conduit.

19. The apparatus as claimed in claims 8, 17 and / or 18 wherein, the fluid outlet provides a recirculation path to the fluid inlet.

20. The apparatus as claimed in any one of the preceding claims comprising: a fluid inlet positioned at or proximal to the first or second electrode; a fluid outlet positioned remote from the fluid inlet to receive fluid which has flowed from the first to the second electrode; and a recirculation path for recirculating fluid received by the fluid outlet to the fluid inlet.21 . The apparatus as claimed in any one of the preceding claims wherein, the conveyor comprises rollers or a gravity feed or a liquid stream.

22. The apparatus as claimed in any one of the preceding claims wherein, the fluid is a conducting liquid.

23. The apparatus as claimed in claim 22 wherein, the conducting liquid is sea water or brackish water.

24. The apparatus as claimed in any one of the preceding claims wherein, the conveyor is configured for transporting live fish along the length of the conduit out of water.

25. A method for stunning fish, the method comprising: transporting a live fish along the length of a conduit in a first direction of travel through a region of the conduit which contains an electrical circuit, the electrical circuit comprising:16a first electrode, a second electrode and a conducting fluid which is extendable between the first and second electrodes in one or more streams to complete the electrical circuit wherein the conducting fluid flows from the first electrode to the second electrode, such that, when a voltage is applied across the first and second electrode, the conducting fluid may apply a shock to stun a fish in the path of the conducting fluid.

26. The method as claimed in claim 25 wherein, the one or more streams are configured to flow in one or more stream between the first and second electrodes with a restricted width, such that the current is provided in the conduit in a well- defined area along its length.

27. The method as claimed in claim 25 or claim 26 wherein, the or each stream has a width of less than 5cm.

28. The method as claimed in claim 25 or claim 26 wherein, the or each stream has a width of less than 3 cm.

29. The method as claimed in any one of claims 25 to 28 wherein, the electrical circuit is positioned such that the conducting fluid flows in a direction across the first direction of travel.

30. The method as claimed in any one of claims 25 to 29 wherein, the electrical circuit is positioned such that the conducting fluid flows in a direction substantially orthogonal to the first direction of travel.31 . The method as claimed in any one of claims 25 to 30 wherein, the method further comprises introducing the conducting fluid via a fluid inlet positioned at or proximal to the first or second electrode.

32. The method as claimed in any one of claims 25 to 31 wherein the method further comprises removing the conducting fluid from the conduit via a fluid outlet positioned remote from the fluid inlet to receive fluid which has flowed from the first to the second electrode.1733. The method as claimed in claim 31 or claim 32 wherein, the fluid inlet creates a jet or stream or sheet of fluid which is extendable between the first and second electrodes.

34. The method as claimed in any one of claims 31 or 33 wherein, the method comprises using a plurality of fluid inlets each of which create a jet of fluid or stream or sheet of fluid.

35. The method as claimed in any one of claims 31 to 34 wherein, a set of fluid inlets are arranged in a plane substantially parallel to the first direction of travel.

36. The method as claimed in any one of claims 31 to 35 wherein, a plurality of sets of fluid inlets are spaced along the length of the conduit.

37. The method as claimed in any one of claims 31 to 36 wherein, the one or more electrical circuit and inlet are selectively switched on.

38. The method as claimed in any one of claims 25 to 37 wherein, a position of fish within the conduit is detectable using a camera.

39. The method as claimed in claim 38 wherein, the camera is connected to a controller such that the electrical circuit and inlet may be switched on in response to information on the detected position of the fish.

40. The method as claimed in any one of claims 25 to 32 wherein, the conducting fluid comprises a sheet of fluid which is extendable between the first and second electrodes across the first direction of travel.41 . The method as claimed in claim 40 wherein, the sheet of fluid extends substantially over the cross sectional area of the conduit.

42. The method as claimed in claim 32 wherein, the fluid outlet provides a recirculation path to the fluid inlet.1843. The method as claimed in any one of claims 25 to 42, the method comprising recirculating the conducting fluid from a fluid outlet to a fluid inlet, wherein the fluid outlet is positioned remote from a fluid inlet and wherein the fluid outlet is configured to receive fluid which has flowed from the first to the second electrode.19

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