Field of the Invention

The invention relates to fish stunning and, in particular, fish stunner apparatus e.g. (referred to as fish stunner(s)) for flow-through fish stunning and methods for use in same. In a further aspect the invention relates to power supplies, apparatus for stunning and methods of stunning for use in fish or other animal stunning, particularly e.g. in saltwater fish stunning. Flow-through fish stunning may also be referred to as pipeline fish stunning as the fish and transport water typically travel through a pipe.

This application claims priority from UK patent application No. GB151 1850.8 filed on 7 July 2015, the entire contents of which are here by incorporated by reference. In particular, if any subject matter or features are present in the priority application UK patent application No. GB151 1850.8 and are not, for whatever reason, present in this application, such subject matter and features are specifically incorporated by reference into this application and may be claimed. Such features, if any, can be precisely defined and are identifiable by comparison between this application and the priority application, and are thought to contribute to solving the technical problem underlying the invention in at least one or more embodiments.

Background to the Invention

Humane slaughter techniques on land based farms have outpaced developments in aquaculture processing. While some common inhumane practices have been banned by EU legislation, for example the use of C02, many farms in Europe still drop 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. 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.

The present applicant, Ace Aquatec Ltd, has previously made and sold a flow-through fish stunner (HS1) 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 1000HZ AC voltage to deliver around 3- 1 1 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. The area of these electrodes in this arrangement meant that it could not be used with saltwater which has a significantly higher conductivity and so current demand than fresh water. In a flow-through fish stunner, the water is not re-circulated and the speed of the flow of water is preferably sufficient to overcome motion of the fish against the flow of the water so that fish are swept along in the direction of flow of the water. A later recirculating fish stunner (HS2) 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 low 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. Nevertheless, the power requirements of this system were not too onerous because of the limited (low) volume and controlled salinity.

However, the recirculated fresh water supply pipeline fish stunner has several drawbacks: it increases the fail rate of stunning due to the detritus that builds up in the water, it limits the quantity of fish that can be stunned per hour (around 10 tonnes per hour), and it stuns at the end of the fish transportation process leading to greater stress in the fish and therefore only modest quality improvements over existing methods. Alternative electric stunners have been built in Norway for salmon which remove the fish from the water but this method increases stress and introduces damage to the fish at the point of contact with the electrodes. At present therefore saltwater species including seabass and seabream remain outside the scope of humane slaughter.

There is, therefore, a need to provide apparatus, systems and methods capable of stunning saltwater species in saltwater in a flow-through system.

There is also a need to provide improved apparatus, systems and methods capable of stunning species in fresh water, or water of any type, in a flow-through system.

GB879314 KREUTZER describes an electrical device which provides a series of short duration electrical pulses in water which stun fish in water. Use in saltwater is not described.

US5327854 SMITH describes electric fish shocking devices for use as fish barriers and fish collectors using programmable output waveforms and, in particular, a power inverter to deliver a variety of voltage levels and supply enough current at each voltage level to electrify sufficient volume of water. A voltage selector provides a means of changing the output voltage to accommodate a wide range of water conductivity. A wide variety of pulse derived waveforms can be produced. The difficulties of providing a power supply for use in saltwater are not mentioned or addressed.

GB2417408 ACE-HOPKINS describes a device for electronically slaughtering fish comprising a stunning station for stunning fish using an electric current in water and a stun maintenance station to maintain the fish in an unconscious state in air after stunning until they leave the stun maintenance station.

GB2502816 MCKIMM describes a method and apparatus for slaughtering fish providing an elongate passage and generating a linear electric field in a first region of the passage to stun fish and applying a further electric field downstream to kill fish. No details of the power supply used are provided. The difficulties of providing power supplies for use in saltwater are not mentioned or addressed. WO2001/95732 ROBB describes a method and device for stunning and killing aquatic animals so that during a first period an electric current with a first current intensity is generated in the animal such that it is stunned and conditioning the water such that the animal remains stunned during a second period.

CA2637860 MOHR describes apparatus for applying electro narcosis to fish in which a transportation means, such as an endless belt, moves fish through a guide means exposing the fish or fishes into contact with current application means such as a plurality of current transmission elements pivotally mounted and freely movable. During fish transport the fish touch the current plates and are exposed to the voltage of each plate. Fish exposure to the voltage intensity required for fish sedation is directly related to fish exposure time to the voltage. This arrangement has the disadvantage that the fish are in physical contact with the belt and/or the current plates potentially risking damage.

LAMBOOIJ et al describe "Evaluation of electrical stunning of sea bass (Dicentrachus labrax) in sea water and killing by chilling: welfare aspects, product quality and possibilities for implementation" in Aquaculture Research, 2008 39, 50-58.

KNOWLES et al describe "Effect of electrical stunning at slaughter on the carcass, flesh and eating quality of formed sea bass (Dicentrachus labrax)" in Aquaculture Research, 2007 38, 1732-1741 .

LINES et al describe "Safeguarding the welfare of formed fish at harvest" in Fish Physiol. Biochem DOI 10.1007/S10695-01 1 -9561 -5.

The European Food Safety Authority has issued "Species-specific welfare aspects of the main systems of stunning and killing formed Atlantic salmon" in The EFSA Journal (2009) 2012, 1 -77, and has "Species-specific welfare aspects of the main systems of stunning and killing of formed seabass and seabream" in The EFSA Journal (2009) 1010, 1 -52.

ROBB et al describe "Brain Activity of Atlantic Salmon (Salmo salar) following electrical stunning using various field strengths and pulse durations" in Aquaculture 2051 (2003), pp 363-369.

LINES et al describes "Electrical Stunning of Fish: The relationship between the electric field strength and water conductivity" in Aquaculture 241 (2004) 219-234.

US5551377 SHARBER describes an apparatus and method for electro-anesthetising fish, in which an electronically insulated water containable member has a first electrode and a pair of second electrodes bracketing the first electrode.

KESTIN describes "Welfare of fish at harvest" in Trout News, No 17, December 1993, Ministry of Agriculture, Fisheries and Food, UK.

COWX et al: Fishing with Electricity, published 1990 by Fishing News Books (a division of Blackwell Scientific Publications Ltd)

BIRD et al describe "The selection of suitable pulsed current for electric fishing in fresh waters" in Fisheries Research 18 (1993) 363-376. HUDY describes "Rainbow Trout and Brook Trout Mortality from High Voltage AC Electrofishing " in the North American Journal of Fisheries Management 5:475-479, 1985.

HOLLENDER et al describe "Injury to Wild Brook Trout by Backpack Electrofishing" in the North American Journal of Fisheries Management 14: 643-649, 1994

WO2006130017 KJOLAAS describes a method and arrangement for applying electronarcosis to fish in which two electrodes are arranged in a channel, which come into contact with fish that move through the channel.

WO0038530 MOLLER describes an apparatus and process for slaughtering fish wherein electronarcosis is induced by exposing the fish to an alternating electrical field having a frequency of greater than 20Hz for a predetermined duration wherein if the frequency is less than 200Hz, the duration is less than 2 seconds and wherein the fish are subsequently killed while unconscious.

JOHN ACE HOPKINS describes "Humane Slaughter of Fish" in Finfish News 7, Winter/Spring 2009.

Previous sources have often relied on low voltage battery or generator power or mains power at its nominal frequency and voltage, which is not optimal, limiting applicability to more general use.

Indeed, the need for commercial electric stunning of saltwater species is well recognised (see recommendations 8 and10 of the EFSA Report (2009) 1010, 1 -52: recommendation 8 -"The opportunity to develop new methods for slaughtering fish is considerable and should be encouraged' and recommendation 10 - "Development of commercial stunning methods to induce immediate (or rapid) stunning methods unconsciousness in sea bass and sea bream is urgently required' .

There is therefore a need to develop a saltwater electrical stunner for rendering fish, e.g. salmon, seabream and seabass, unconscious prior to slaughter, preferably for rendering fish unconscious prior to slaughter consistently, swiftly and humanely.

Further, there is, therefore, a need to develop a high power electric saltwater stunner in line with the fish transport pipe in a flow-through arrangement.

Further there is a need to develop apparatus and methods for producing better quality fish carcasses from harvesting processes.

Statement of Invention

In one aspect the invention provides a fish stunner comprising a high power alternating voltage power supply, stunning electrodes and transportation means configured to create electric fields in transported water, preferably saltwater for the purpose of stunning fish, preferably saltwater, fish unconscious. Preferably the fish stunner comprises: a high power alternating voltage power supply; a plurality of stunning electrodes; and a stunner tube; and means for transporting fish through the stunner preferably comprising at least saltwater; whereby the fish stunner is configured to create electric fields in transported (salt)water for the purpose of stunning (salt)water fish unconscious. Preferably the fish stunner comprises: an elongate stunner tube; a plurality of stunning electrodes along the tube; a high power alternating voltage power supply configured to supply OV (e.g. with respect to ground potential) to at least one stunning electrode and at least one high power alternating voltage to at least one stunning electrode; means for transporting fish through the stunner tube preferably comprising at least (salt)water; whereby the fish stunner is configured to create alternating electric fields in transported (salt)water within the stunner tube for the purpose of stunning (salt)water fish unconscious.

In a first aspect of the invention there is provided a flow-through fish stunner for use in saltwater flow- through fish stunning comprising: an elongate stunner tube configured so that water can flow, e.g. by pumping, through the tube in a flow-through manner; at least three stunning electrodes spaced along the stunner tube configured to provide, when powered, an electric field (preferably substantially longitudinally along the stunner tube); a high power alternating voltage power supply configured to supply Ov to at least one stunning electrode and further configured to supply at least one high power alternating voltage to at least one remaining stunning electrode; whereby high power alternating voltage electric fields are provided along part or substantially all of the stunner tube (e.g. between the first stunning electrode and the last stunning electrode).

In one embodiment there is provided a flow-through fish stunner in which the elongate stunner tube is configured so that (salt)water and fish, preferably a predetermined species of fish, can flow through the tube in a flow-through manner at sufficient speed to overcome any motion of the fish against the flow of water; and comprising at least four stunning electrodes spaced along the stunner tube configured to provide, when powered, an electric field substantially longitudinally along the stunner tube; and, a high power alternating voltage power supply configured to supply OV to at least two stunning electrodes and further configured to supply at least one high power alternating voltage to the remaining stunning electrodes; and in which at least the first and the last electrode in the direction of flow being at OV. This facilitates provision of high power alternating voltage electric field along part or substantially all of the stunner of sufficiently high field strength to stun a predetermined species of fish, preferably saltwater fish, transported in the water, preferably saltwater, unconscious.

Preferably, the high power alternating voltage power supply is configured to supply at least one high power alternating voltage to all the remaining stunning electrodes.

Preferably, the high power alternating voltage power supply, is configured to supply Ov to at least two stunning electrodes.

Preferably, the at least two electrodes at Ov comprise at least one upstream (e.g. the first) stunning electrode and/or at least one downstream (e.g. the last) stunning electrode in the direction of flow.

Preferably, high power alternating voltage electric fields are provided between each neighbouring pair of stunning electrodes along part or substantially all of the stunner tube (e.g. between the first stunning electrode and the last stunning electrode). Preferably the upstream and downstream stunning electrodes held at OV by the power supply are preferably also the first and last stunning electrodes in the direction of flow. Preferably the upstream and downstream stunning electrodes held at OV by the power supply are also the first and last electrodes in the elongate tube.

Preferably the electric field is substantially symmetrical about a central longitudinal axis of the tube. The electric field(s) are preferably substantially longitudinal along the stunner tube but may be transverse and/or diagonal. Preferably the electric field is substantially uniformly distributed across the cross-section of the stunner tube.

It will be understood by those skilled in the art that one or more further (non-stunning) electrodes, e.g. connected to ground, may be provided upstream of the first stunning electrode, and/or one or more further (non-stunning) electrodes e.g. connected to ground may be provided downstream of the last stunning electrode.

In a further aspect of the invention there is provided a method of stunning fish comprising: providing an elongate stunner tube configured so that water preferably saltwater can flow-through the tube in a flow-through manner; providing at least three stunning electrodes spaced along the stunner tube configured to provide, when powered, an electric field substantially longitudinally along the stunner tube; providing a high power alternating voltage power supply, configured to supply Ov to at least one stunning electrode and, further configured to supply at least one high power alternating voltage to at least one remaining stunning electrode; providing high power alternating voltage electric fields along part or substantially all of the stunner tube; flowing water bearing fish through the stunner tube preferably in a flow-through manner; stunning fish in the high power alternating electric field.

Preferably the speed of the flow of water through the apparatus is sufficient to overcome any motion of that species of fish in a direction against the flow, so the net direction of motion of the fish, is in the same direction as the flow of water.

Optionally, the method comprises flowing (e.g. pumping) water bearing fish through a stunner tube in a flow-through manner; stunning the fish in a stun station using a first high power alternating electric field; maintaining the stun in a stun maintenance station using a second high power alternating electric field, preferably from the same power supply; preferably removing water from the stunner tube for disposal and fish for further processing. Optionally, transport of the fish may be via the water flow and/or by conveyor means.

In a further aspect of the invention there is provided a power supply for use in flow-through fish stunner apparatus and methods, e.g. especially in saltwater, configured to deliver at least one high power alternating voltage for stunning fish e.g. stunning fish unconscious swiftly and maintaining the stun until death (which may be via other means e.g. ice or bleeding). The power supply may be used in various flow-through arrangements and also be used in batch (tank based) and re-circulation fish stunning methods, and may also be used in other animal stunning apparatus and methods. In a further aspect there is provided use of a power supply according to any of the claims, and/or as described herein, for stunning fish and/or other animals.

In a further aspect there is provided a method of stunning fish or other animals comprising: using a power supply according to any of the claims, and/or as described herein, to stun fish and/or other animals.

In a further aspect there is provided a method and a stunner for stunning fish or other animals comprising:

- stunning, or means for stunning, fish (or other animals) using at least one high power

alternating electric field; wherein the electric field is configured to alternate at <125Hz, and/or <100Hz, and/or <50Hz, and/or <25Hz and/or between 10 to 50Hz, and/or between 20 to 40Hz, and/or between 25 to 50Hz, and/or at 25Hz, and/or at 50Hz.

Any feature of any embodiment of any aspect may be used in any embodiment of any other aspect of the invention as would be understood by someone skilled in the art.

Preferably the fish stunner comprises at least four stunning electrodes or at least five stunning electrodes. Preferably the stunning electrodes are annular stunning electrodes.

Preferably the first electrode and at least the second electrode in the direction of flow form a stun station. Preferably the last electrode and at least the next to last electrode in the direction of flow form a stun maintenance station. Preferably the fish stunner comprises a stun station and a stun maintenance station and the stun station is upstream of the stun maintenance station. Preferably in the direction of flow, the last electrode of the stun station forms the first electrode of the stun maintenance station. Preferably, the electric field at the upstream end (e.g. in the stun station) has a higher strength electric field able to render a fish rapidly unconscious and an electric field at the downstream end (e.g. in the stun maintenance station) which is of lower strength and so able to maintain the state of unconsciousness but not typically strong enough to render a conscious fish rapidly unconscious. Where provided a stun station is preferably adjacent, and more preferably contiguous with a follow on stun maintenance station. Preferably the same stunning tube provides both.

Preferably at least two neighbouring stunning electrodes in the direction of flow within the stun station are at a first predetermined separation L1 and at least two neighbouring stunning electrodes in the stun maintenance station in the direction of flow are at a second predetermined separation L2, and in which L2 is greater than L1 . Preferably, L2 is in a predetermined ratio to L1 whereby the electric fields in at least part of the stun station have a predetermined ratio to the electric field in the stun maintenance station (e.g. to provide a lower electric field). Preferably the length of L2 is over one times, two times or three times or four times the length of L1 . This arrangement facilitates the use of a limited number of alternating voltage(s) from the same high power alternating voltage power supply to be used over larger lengths of stunner tube by varying the distances between stunning electrodes to produce different electric fields e.g. a lower stun maintenance field. Optionally at least two neighbouring stunning electrodes in the stun maintenance station are at a third predetermined separation L3. For example, L2 may be greater than L3, particularly when the stunning electrodes defining L2 have greater voltage difference than those of separation L3. It will be understood that it is the electric field strength developed in the volume that is important for stunning and stun maintenance and this depends on a number of factors including number of stunning electrodes, applied voltage and phase of the voltage as well as electrode separation. It will be understood that the speed of water flow in a flow-through stunner is necessarily quite swift and so to ensure sufficient duration of stun e.g. in a stun station and in a later stun maintenance section, the fish stunner must be quite long. Therefore to ensure sufficient duration of stun (stun conditions and timings depend upon species) e.g. 2-30s, 5- 30s, 2-25 s, 10-30s, 15-30 s and so on, for example in the stun maintenance section, the stunner tube must be commensurately long in total, even if the stunner tube is presented in two stunner tube sections one after the other. This requirement for a lengthy stun presents unique challenges for stunning in water in general and saltwater in particular, which the present invention seeks to address.

Preferably the fish stunner comprises stunning electrodes in the stun maintenance station which are equi-spaced. This is particularly effective when using an odd number of stunning electrodes.

Preferably an alternating electric field is provided between each stunning electrode (e.g. by providing it with Ov, V1 , V2 or different phases) and its neighbouring electrode upstream and/or its neighbouring electrode downstream. Preferably for an even number of stunning electrodes, each electrode between first and last is powered differently from its neighbours (optionally with different voltages and/or different phases) so as to provide an alternating electric field along part or substantially all of the length of the stunner tube.

Preferably the stunning electrodes are grouped into groups; a first group with stunning electrodes at Ov, and at least one further group with stunning electrodes at a first alternating voltage so as to provide an alternating field between each pair of neighbouring stunning electrodes.

Preferably the fish stunner comprises an odd or even number of stunning electrodes and comprises a first group of two or more stunning electrodes at Ov, a second group of stunning electrodes at a first alternating voltage and a third group of one or more stunning electrodes at a second alternating voltage.

Preferably an odd number of stunning electrodes are provided and the first group at Ov comprises the first and last stunning electrodes and each alternate electrode between first and last stunning electrodes.

Preferably the high power alternating supply comprises one or more transformers.

Preferably the high power alternating voltage power supply is powered by a single phase power supply and comprises one, two or three single phase transformers. Preferably the high power alternating voltage power supply is provided by a three phase supply and comprises a three phase transformer and/or at least two single phase transformers.

Preferably an odd or even number of four or more stunning electrodes are provided and neighbouring stunning electrodes are connected to different phases and/or Ov so that each pair of neighbouring stunning electrodes are provided with an alternating electric field therebetween and/or so that no two neighbouring stunning electrodes are provided with the same voltage at the same time.

Preferably the power supply supplies two different high power alternating voltages. One of these may be for the stun station and one for the stun maintenance station provided e.g. by different single phase transformers or different phases and/or taps from a three phase transformer.

Preferably the power supply comprises two single phase transformers of different power ratings (e.g. so that one transformer can deliver more, e.g. a multiple (e.g. twice) the current than that of the second transformer).

Preferably the distance between stunning electrodes in the stun station is less than that between stunning electrodes in the stun maintenance station so that when the same alternating voltage is used in each of the stations, the electric field (voltage gradient) is commensurately different between their respective stunning electrodes.

Preferably the high power alternating voltage power supply is configurable so that the peak output voltage and/or RMS output voltage and/or frequency and/or output voltage waveform can be selected, and comprises an output inverter configured to provide at least one predetermined alternating voltage.

Preferably the power supply provides an alternating voltage with a sinusoidal, and /or square, and/or smooth square, and/or quasi-square waveform. Preferably the alternating voltage has a frequency of 5Hz to 10000Hz and/or 5Hz to 2000Hz and/or 5Hz to 1000Hz and/or 5Hz to 250Hz and/or 100Hz to 200Hz and/or <125Hz. More, preferably the alternating voltage has a frequency lower than 125Hz. More preferably, the alternating voltage has a frequency of 10 to 50Hz and/or 20 to 40 Hz, and/or 25 to 50Hz, and/or 10Hz, or 20 Hz or 25Hz. It is thought these lower frequencies may be particularly suitable for certain embodiments of this invention. Preferably the alternating voltage alternates about Ov.

Preferably the peak voltage of the voltage output is between 100V and 600V or is between 200V and 600V or is between 250V and 600V or is between 300V and 600V. Preferably the rms voltage per meter is between 12 Vrms/m and 800 Vrms/m or is between 15Vrms/m and 500Vrms/m, or is greater than or equal to 12Vrms/m or is greater than or equal to 15Vrms/m or or is greater than or equal to 15Vrms/m or is less than or equal to 800Vrms/m or is less or equal to 500Vrms/m or is less than or equal to 400Vrms/m.

Preferably the high power alternating voltage power supply is configured to deliver at least 3kW and/or at least 5kW and/or at least 7 kW and/or at least 12kW and/or at least 14kW and/or at least 15kW and/or at least 16kW or 5kW to 40kW or 5kW to 25kW or 7kW to 20kW. Preferably the elongate stunner tube comprises a pipe (or two or more, or preferably several, in-line pipe sections). Optionally, the elongate stunner tube may comprise multiple separate sections, e.g. pipe sections that are adjacent and contiguous with one another to form the pipe or which are in line but not contiguous forming two separate stunner tube sections. Typically, the pipe forming the stunner tube may have for example a continuous periphery (e.g. closed pipe). Preferably the elongate stunner tube is circular in cross section. Preferably the elongate stunner tube has a substantially fixed cross- sectional area, or average cross-sectional area e.g. when corrugated, along part or all of its length (e.g. between the first and last stunning electrodes).

It will be understood by those skilled on the art that saltwater can have various salinities and associated conductivities. For example, Wikipedia ("Fresh Water" retrieved 23 Sept 2015) describes fresh water as less than 500ppm (<0.05%) of dissolved salts, brackish water as 500-30, OOOppm (0.05%-3%) which is roughly equivalent to conductivity of around 800-50,000 με/αη, saline water as 30, 000-50, OOOppm (3-5%) which is roughly equivalent to conductivity of around 50,000-80,000 μβ/ατι and brine as more than 50, OOOppm (>5%) which is roughly equivalent to conductivity of greater than around 80,000 με/ατι. Salinity is ^use d by oceanographers as a measure of the total salt content of seawater. Practical salinity, symbol S, is determined through measurements of the electrical conductivity and iernperature of seawater, which are interpreted by an algorithm developed by the United Nations Educational Scientific and Cuiturai Organization (UNESCO). The measure of practical salinity (psu although strictly this is a unit-less quantity) was originally developed to provide an approximate measure of the total mass of salt in one kilogram of seawater. Seawater with S equal to 35 contains approximately 35 grams of salt and 965 grams of water, or 35 ppt (35 psu).

So for example, tap water is typically 20 - 560 ppm, and this is equivalent to 0.02 - 0.56 psu and conductivities of 30 - δθθμε/ατι at 10°C. The salt concentration limit in the US for drinking water is 10OOppm which is 1 psu or equivalent to a conductivity of 1400μ5/ατι at 10°C. The typical limit for agricultural irrigation is 2000 ppm which is 2 psu or equivalent to a conductivity of 2700 με/ατι at 10°C. Sea water is typically 35,000 ppm and this is equivalent to 35 psu and conductivity of

380υΌμ8/αη at 10°C.

In this application the term saltwater is, unless the context indicates otherwise, intended to exclude water having those ranges of dissolved salts and conductivities attributable to fresh, or useable agricultural, water. Thus saltwater is intended to cover water having salinity and corresponding conductivity which starts to present a problem for stunning in that type of water (at the temperature at which it is expected to be used). Therefore, the term saltwater water includes more brackish water, saline and brine water, unless the context indicates otherwise, having dissolved salts and associated conductivities over generally accepted limits for fresh water, and optionally also over generally accepted limits for agricultural water, for example having conductivities of greater than around 3000 με/ατι at 10°C. Preferably the fish stunner, and/or stunner tube, is adapted for use with saltwater of conductivity greater than 300C^s/cm, or greater than δΟΟΟμε/αη, or greater than Ι Ο,ΟΟΟμε/οηι, or greater than 20,00C^s/cm or greater than 30,00C^s/cm or greater than 40,00C^s/cm or greater than δΟ,ΟΟΟμε/οηι.

Preferably the fish stunner, and/or stunner tube, is adapted for use with saltwater of salinity between 10 to 50psu, or between about 10psu to about 50psu. The power requirements are now significant to have an effective stun, and preferably also maintenance of stun, in a flow through fish stunner.

It will of course be understood that conductivity of water varies greatly with temperature, but that salinity and temperatures of water sources, e.g. sea water, sea lochs, fresh water lochs, do not vary significantly over the course of a day, month, or year (except in some more unusual geographic situations), therefore in a particular location the conductivity of the water can be predicted to be generally the same. It is intended that the conductivities for which the fish stunner is adapted will provide for, or preferably encompass, the typical conditions e.g. salinity and temperature of a particular location, since it is preferred that the water in which the fish are found is the same water that is used in the fish stunner so as to stress the fish less.

Preferably the stunner tube comprises an elongate tube of diameter 200mm, 250mm, 300mm or 8" 10" or 12" or 14" or 15". The greater the length or width of the stunner tube, then the greater are the power requirements. Preferably, the fish stunner is configured to cooperate, preferably, in-line, with an inlet of a fish pump. Alternatively or in addition, the fish stunner is configured to cooperate, preferably, in-line, with an outlet of a fish pump. Thus, the stunner tube may be adapted to connect directly to the inlet and/or outlet pipes of a fish pump. Alternatively or in addition fish pump (vacuum pump) could be configured to allow the fish to be stunned early in the transportation process, so that fish will be unconscious at the point they enter the pump, reducing stress and improving quality.

Preferably the stunning electrodes are located in an internal recess about the internal surface of the elongate stunner tube. Preferably the stunning electrodes are substantially perpendicular to the direction of water flow through the passage.

Preferably the fish stunner comprises: a stun station of a first predetermined length having a first predetermined alternating electrical field therein for stunning fish into an unconscious state; and, a stun maintenance station of a second predetermined length and a second predetermined alternating electric field therein for maintaining fish in an unconscious state.

Preferably, the method comprises any of the features of described herein and/or in any of features of the claims.

Preferably, the method comprises: providing an elongate stunner tube configured so that water can be flowed (e.g. pumped) through the stunner tube in a flow-through manner; providing at least three stunning electrodes, more preferably four or five stunning electrodes, at least one of the stunning electrodes being at Ov (e.g. the first and/or last): the first and second stunning electrodes in a direction of flow forming a stun station; at least the next to last and last stunning electrodes in a direction of flow forming a stun maintenance station; providing and powering a high power alternating voltage power supply to power the stunning electrodes so as to provide an alternating (preferably

substantially longitudinal) electric field along part, or substantially all, of the tube; and powering the stunning electrodes to provide the said alternating electric field so as to cause the fish to be rendered unconscious in the stun station and maintained in an unconscious state in the stun maintenance station.

Preferably the power supply comprises at least one transformer configured to deliver at least 3kW, or at leats 5kW, or at least 7kW or at least 10kW or indeed 12kW or at least 14kW or at least 16kW. Preferably the power supply comprises a single phase power supply and one, two or three single phase transformers. Preferably, the power supply comprises a three phase supply and a three phase transformer and/or at least two single phase transformers.

Preferably the power supply comprises: an AC to DC rectifier module configured to convert at least one industrial supply (mains AC and/or generator AC/DC supply) to low voltage DC output; an isolated DC to DC converter configured to step up the low voltage DC input to a high voltage DC output; and, an output inverter module configured to convert DC to at least one predetermined alternating voltage (e.g.AC) waveform.

Preferably the power supply is configurable and can supply at least one alternating voltage of varying configuration (configurable in e.g. peak voltage and/or rms voltage and/or frequency and/or waveform).

Preferably the power supply comprises any of the features of described herein and/or in any of the claims. The power supply(ies) of one or more embodiments of the invention can be used in various stunning applications e.g. as described herein.

A flow-through fish stunner is one in which water (preferably bearing fish to be stunned) is flowed, e.g. pumped, from an entrance of a stunner tube to an exit after which it is disposed of e.g. at a de- watering station. Thus, water is not recirculated. Optionally, further fish transporting means (e.g. a conveyor belt) may be provided but this is less preferred. To avoid fish swimming out of the stunner tube, preferably the flow of water is quite fast, so the tube is necessarily quite long to ensure sufficient stun time, increasing the power requirements drastically. Some de-watering before the flow-through fish stunner may take place. Preferably, the stun maintenance station is from the second to the last electrode but it may be from a later electrode to the last electrode in the direction of flow. A fish pump may be provided before or after the fish stunner, i.e. before or after the elongate stunner tube. This may be an air pump, vacuum pump, centrifugal pump or similar pump. The stunner tube is preferably in line with the pump inlet/outlet pipes. The stunner tube may be provided by one or more circular plastic pipe(s) e.g. flexi-pipe of PVC or HDPE). Typically the pipe is of consistent diameter along the stunning length. It may be of 50-300mm in diameter and is preferably 150-250mm or more or preferably 200mm in diameter. Preferably, some of the water after transportation (or removal from a fish farm etc) and immediately before the fish stunner is removed to reduce the volume of water going into the stunner.

It will be understood by those skilled in the art that fish may be stunned along their bodies from head to tail (preferably head first) or across their bodies. In a flow-through fish stunner with pumped water flowing through a stunner tube, elongate fish typically travel with their elongate body in-line with the longitudinal axis of the stunner tube and preferably head first. Where conveyors are used, e.g. with flat fish, this is not necessarily the case, so a longitudinal field along the stunner tube may provide a transverse field across a fish if the fish is lying transverse to the long axis of the conveyor belt.

Optionally, the invention comprises various aspects and embodiments of the invention, such as the fish stunner, stunner apparatus, method(s), power supply(ies), in which any feature which cannot, explicitly or implicitly, be directly and unambiguously derived using common general knowledge from the priority application GB151 1850.8 as filed, is expressly excluded from that aspect or embodiment of the invention as claimed.

In a further aspect of the invention, the fish stunner(s), stunning method(s) and power supply(ies) as described and claimed herein may be used or configured for use with fresh water. This configuration may be minimal as the power requirements for fresh water are so much less onerous.

Brief Description of the Invention

The invention will now be described by way of example only with reference to the following Figures in which like reference numerals refer to like features. It will be understood by those skilled in the art that the following descriptions represent examples of how the invention may be carried out in practice and other embodiments can be envisaged from the description herein. Any feature from any one or more aspects of the invention may be combined with any other feature in any one or more aspects and/or embodiment of the invention.

Figure 1 shows a schematic view of a flow-through fish harvest production line illustrating a flow- through fish stunner operating in line with the fish transportation pipe in a harvest production process (here, on-site adjacent a fish farm).

Figure 2 shows a schematic diagram of a fish stunner with a fish stunner passage, in the form of an elongate electrifiable stunner tube comprising a tube and three stunning electrodes spaced along it and powered using a three phase supply, a three phase transformer and two conductor arrangement.

Figure 3 shows a schematic diagram of a three electrode flow-through fish stunner powered by a single phase supply and a single transformer using two conductors.

Figure 4 shows a schematic diagram of a four electrode flow-through fish stunner comprising a power supply powered by a three phase supply and comprising a three phase transformer for powering four stunning electrodes using three conductors. Figure 5A shows a schematic diagram of a flow-through fish stunner with five stunning electrodes comprising a power supply powered by a three phase supply and comprising a three phase transformer for powering the five stunning electrodes using three conductors.

Figure 5B shows a similar arrangement to Figure 5A but using a three phase transformer (not shown) to power five stunning electrodes using two conductors (cf. also to Figure 2).

Figure 6 shows a schematic diagram of a flow-through fish stunner with four stunning electrodes and a power supply powered by a three phase supply and comprising two single phase transformers to power the four stunning electrodes via three conductors.

Figure 7 shows a schematic diagram of a five electrode flow-through fish stunner having a power supply powered by a three phase supply and comprising two single phase transformers for powering the five stunning electrodes using two conductors.

Figure 8 shows a schematic diagram of a five electrode flow-through fish stunner having a power supply powered by a single phase supply and comprising a single phase transformer to power the five stunning electrodes using two conductors.

Figure 9 shows a schematic diagram of a five electrode flow-through fish stunner comprising a power supply powered by a single phase supply and comprising two single phase transformers to provide power to the five stunning electrodes using three conductors.

Figure 10 shows a schematic diagram of a fish passage, in the form of an elongate stunner tube 90 for a five electrode flow-through fish stunner comprising spaced annular stunning electrodes and illustrating alternating electric field lines between the stunning electrodes along substantially the entire length of the tube.

Figure 1 1 shows a schematic of a configurable high power alternating voltage power supply for powering stunning electrodes in a flow-through fish stunner, according to one or more aspects of the invention.

Figures 12A and 12 B show example waveforms capable of being delivered by the one or more embodiments of the high power alternating voltage power supply of the invention for use in flow- through fish stunner(s) and method(s) of the invention.

Detailed Description of the Invention

Most commercial fish harvesting methods do not make use of electric stunning. Depending on species and other factors, methods of harvesting include asphyxiation, exsanguination, C02 and percussive stunning. Large fish can be percussively stunned with mechanical apparatus, but smaller fish are more difficult to handle and are often put straight into ice buckets. Supermarkets and consumers consider this unethical. Electric stunners are available but typically for limited volumes of water. Batch methods using small tanks with a limited volume of water are unsuitable for commercial harvesting. Electric stunners designed to render fish unconscious in 1 second, prior to a slaughter method, such as ice or bleeding, are considered more humane.

Precise electrical parameters (in terms of electricity type (AC and/or DC), frequencies (Hz) and voltages must be applied to the fish to render them unconscious. In batch methods in a small tank, the required voltage and currents can be easily applied because the power required to electrify that volume of water is relatively small. As the system is up-scaled to include larger quantities of water, then the power requirements go up drastically. Furthermore, if the tank is inappropriately designed, fish closer to the stunning electrodes may be heavily stunned whilst those further away may only be lightly stunned.

The present applicant developed the first electrical pipeline stunner in 2004 to stun trout - a fresh water fish. In a flow-through process, a pump moves fish from cages and passes these into a specially constructed pipe with opposing stunning electrodes providing transverse electric fields across the diameter of the pipe. Because of the low conductivity of fresh water, low power suffices and the stunning electrodes can be powered with a class D amplifier or multiple class D amplifiers. This works for low power stunning in fresh water.

To slaughter fish in saltwater is an entirely different proposition in terms of power, the conductivity of fresh water being in the range typically of δθμε/ατι to δθθμε/ατι whereas the conductivity of sea water can be in the range typically of δΟ,ΟΟΟμε/ατι to δΟ,ΟΟΟμε/αη, an increase of 2 to 3 orders of magnitude (100 to 1000 times greater). Higher conductivity means that for the same electric field, more current will flow, increasing the power requirements drastically.

A D class amplifier approach would require multiple such amplifier units attached to a great many stunning electrodes to provide the required electric fields in saltwater of very high conductivity. To get round this, one embodiment of the present invention proposes using industrial single or industrial three phase power, which requires more skill and knowledge to manipulate into the appropriate voltages and frequencies to render the particular fish species unconscious in the particular conductivity of the transporting water.

In one or more embodiments, the present invention does not rely on recirculating water supply of limited volume nor on controlled salinity to reduce the power required to generate the precise electrical voltages and frequencies required between the stunning electrodes. In at least one embodiment the present invention creates the required electric field in whatever water supply the fish are pumped.

One or more embodiments of the present invention provide high power modules that meet the low voltage and electromagnetic induction (EMI) regulations as well as providing a robust system capable of managing high voltages (e.g. 600 volts) and currents (e.g. 50 amps).

Thus, in one embodiment, a high power alternating voltage power supply provides voltages of the required parameters to render species unconscious within 1 second in saltwater, and to maintain the stun period to create the required lengths of insensibility for them to be killed humanely e.g. in ice. In at least one embodiment the invention will be flexible enough to be extended to other larger fish species, (salmon, seatrout, yellowtail etc.) bringing the fish stunner apparatus into direct competition with percussive stunners. In at least one embodiment, flexible power input will allow the systems to operate in many countries, using for example pulse width modulation (PWM) electrical conversion and controls to enable a vast range of parameters (AC, DC, frequency, voltage and timing controls) to be applied to help improve quality after stunning.

To date the transportation and stunning of fish has been a two stage processes, with the latter occurring subsequent to pumping into the harvesting station and dewatering; however fish are inevitably stressed, which has a knock on effect for quality. The present invention proposes a stunning system to offer a strategy for stunning fish as soon as they leave the holding pen, stunning them quickly and in water, making it an attractive system for all commercial fish species and to welfare legislators.

KNOWLES et al (2007) "and LAMBOOIJ et al. (2008), provide comment on the parameters required to stun seabass and bream both in small tubs using modest power amplifiers, and in a recirculation system where the conductivity of the water is carefully controlled.

In at least one embodiment the present invention proposes scaling up the power of the system significantly so that the same electrical parameters can be achieved across a 200mm pipe in saltwater drawn from a fish pen along a 30m transport pipe. In at least one embodiment the present invention provides for a 15Kw system to supply voltages for insensibility to two stunning electrodes and power to a further three stunning electrodes supplying the required maintenance field. Typically, a series of alternative electric fields supply AC electricity to stun fish; however in at least one embodiment the present invention uses a range of DC (e.g. pulsed DC) and/or AC options for specific species.

Figure 1 shows a flow-through fish harvest production line 100 incorporating an in-line flow-through fish stunner 32 situated part way along the fish transport pipe(s) 22, 28 (here before a fish pump 24). Fish production line 100 is provided on working platform 40. The in-line nature of the fish stunner 32 enables the production line 100 to be located adjacent to a body of water 21 , such as a fresh or sea water loch or the sea, in which fish are farmed. The production line 100 comprises a pump inlet hose 22 leading to fish stunner 32 and then fish pump 24 (although the fish stunner could be provided after the pump). Fish 20 are pumped from a body of water 21 via pump inlet hose 22 and via flow-through fish stunner 32 and fish pump 24 into a pump outlet hose 28. A further portion of pump outlet hose 28 leads to a dewatering box 36. Water is not re-circulated, although the power supplies described herein may find application in re-circulating fish stunners and other stunning apparatus and methods. Once stunned in the flow-through fish stunner 32, fish may be dispensed onto a working platform 34 or straight into bins 38 loaded with ice water. A generator or a mains power supply (not shown) may be used to provide power to flow-through fish stunner 32. Examples of flow-through fish stunners are shown in Figures 2 to 1 1 comprising mains or generator powered high power alternating voltage power supplies and various numbers and configurations of stunning electrodes arranged into groups so as to be powered by a given number of conductors 54 (54A, 54B, 54C). Each flow-through fish stunner 32 comprises a stunner tube 90. Stunner tube 90 is elongate and comprises at least part of or substantially all of an elongate tube 42 and at least three or more preferably at least four or five stunning electrodes 10 (numbered in the direction of flow as stunning electrodes 1 , 2, 3, 4, 5, etc.) spaced longitudinally along tube 42 to form an electrifiable stunner tube 90. Elongate tube 42 may be formed from a single (e.g. plastic circular) pipe or from a series of joined plastic pipe sections. Elongate tube 42 (forming stunner tube 90) is shown linearly in Figures 2 to 1 1 . Nevertheless, it would be understood by someone skilled in the art and as shown in Figure 1 that elongate tube 42 may be curved and may follow a circuitous route. For example, elongate tube 42 may comprise a number of generally horizontal loops superimposed one upon the other. The loops may be circular as shown in Figure 1 or indeed may be oval or elliptical or spiral etc. The entrance to elongate tube 42 may be low down and the exit e.g. into fish pump 24 may be high up or vice versa although this is less preferred. Thus, elongate tube 42 may thus be looped to provide a smaller footprint.

Nevertheless, even if stunner tube 90 (elongate tube 42) is formed into loops, it is possible to define a longitudinal central axis substantially equally spaced from the inner walls of stunner tube 90.

Preferably, the electric field(s) will be a longitudinal electric field along the longitudinal central axis and substantially symmetrically (and more or less evenly) dispersed about this axis in a plane transverse to it, e.g. by the provision of annular stunning electrodes. When stunner tube 90 is curved, or formed into loops, its central longitudinal axis is similarly curved or formed into loops. Stunner tube 42 is preferably continuous about its periphery and also preferably circular in cross section although other shapes of cross section such as oval or square or rectangle can be envisaged. Whilst less preferred, elongate tube 42 of stunner tube 90 may be provided by open passages or channels such as U or V shaped channels or pipes, but preferably with a lid to prevent inadvertent human access to the (relatively) high voltages present within. Thus, the stunner tube may comprise a fish channel or fish passage or other water carrying channel or passage of any suitable shape of cross-section capable of carrying water (especially saltwater) and fish or other animals to be stunned in a flow-through manner. The term "tube" should therefore be interpreted in a broad manner. Nevertheless, a preferred embodiment of the stunner tube and in particular the elongate tube of stunner tube 90, is a pipe (or pipe sections) having a continuous circumference. Any shape of cross-section of pipe may be used, but circular is preferred. The pipe typically has a constant diameter (or average diameter). The pipe may be corrugated to facilitate the formation of curves and loops.

Stunning electrodes 10 (stunning electrodes 1 , 2, 3, 4, 5, etc.) are preferably annular stunning electrodes e.g. formed from rings of conductive material such as metal. Preferably, the annular stunning electrodes have a constant cross sectional area and shape around the annulus, and are continuous about the circumference of the tube 42. Alternatively, annular stunning electrodes may be provided by multiple spaced stunning electrodes placed in an annular fashion about the circumference or periphery of elongate tube 42 e.g. a pair of crescent shaped stunning electrodes connected together or stunning electrodes on opposing side walls of the tube 42, also connected together electrically to form a single electrode. Stunning electrodes 10 are typically recessed into electrode housings 44 on elongate tube 42 (typically circular pipe) to provide stunner tube 90.

In a further aspect, the power supply(ies) of the present invention may be used with other types of stunner (e.g. re-circulation stunners or fresh water stunners) or with stunners such as those comprising partly, or substantially, transverse electric fields across the tube (between more or less directly opposing stunning electrodes). Indeed, in a further aspect the power supply(ies) of the invention could be used with a diagonal electric field within the tube (with transverse and longitudinal, perhaps even substantial longitudinal, components) between longitudinally spaced apart opposing (facing but not directly opposite) stunning electrodes on the opposing internal side walls of the tube. In a further aspect the power supply(ies) of the invention could be used with batch (tank based) and/or recirculation stunning apparatus for stunning other types of fish such as flat fish which would typically need to be conveyed on an endless belt (conveyer) belt through water e.g. in a tank or recirculation apparatus.

Preferably, stunning electrodes 10 (1 , 2, 3, 4, 5, etc.) are configured so that when powered a substantially longitudinal electric field is provided along part, most or substantially all the stunner tube 90. This is shown in more detail in Figure 10. Typically, the longitudinal electric field runs along substantially all of the elongate tube 42 with minimal or few gaps. This can be achieved by preferably ensuring all the stunning electrodes 10 (1 , 2, 3, 4, 5, etc.) are all continuously powered and interlinked so that electric fields are always present between each neighbouring pair of stunning electrodes.

Nevertheless, as can be seen in Figure 10, regions of low electric field (fewer field lines) around the centre of the annular electrodes can be seen. Preferably, the annular electrodes are configured so that these regions of low field round their centre are not so long (along the tube), and/or so wide (across the tube) and/or so numerous that fish are likely to regain consciousness as they pass through these. Indeed, it is conceivable that there might be other short gaps of reduced or minimal field along the stunner tube 90. For example, neighbouring stunning electrodes powered by the same output from the power supply will, if provided, have no electric field between them. Preferably, any such gaps are sufficiently small in length along the tube that that in passing through any such regions, the fish do not have time to regain consciousness. For example, if one intermediate (or end) electrode has a closely spaced electrode next to it, and both of these electrodes are connected to the same output of the power supply (e.g. V, or V1 or V2 or Ov) then no alternating field is provided between these closely spaced neighbouring electrodes. Preferably, the alternating field is provided along sufficient length of the stunner tube 90 that at typical flow speeds and fields for that species, fish do not have time to regain consciousness as they travel through the tube from entrance to exit, even if one or more short regions of the tube have low or no field present along it. The length of time during which the absence of an electric field may allow fish to regain consciousness will depend on the species and the initial stunning electric field, and any later stun maintenance electric field, and other factors. In this way, alternating electric field sufficient to stun fish for their journey through the stunner tube is therefore provided preferably along at least part or substantially all of stunner tube 90. The stunning electrodes may be configured so as to provide a swift stun in 1 -2 seconds in a stun station and a maintenance stun of for example, 5-25s, or 10-30s, or 15-30s, or 15-20s, or similar in a downstream stun maintenance station.

It will be understood by those skilled in the art that by "alternating voltage" is meant a varying voltage that oscillates in a time varying manner between at least two voltage levels of any polarity, including, but not limited to, AC and pulsed DC. Examples of this include the voltage waveforms described herein. Similarly, an "alternating electric field" is an electric field that oscillates in a time varying manner, for example between two electrodes; the alternating electric field being generated by an alternating voltage oscillating between at least two voltage levels of any polarity, the alternating voltage applied to one electrode with, typically, the other electrode earthed at Ov or oscillating at a different phase between at least two voltage levels of any polarity. By "alternating voltage power supply" is meant a power supply capable of delivering at least one varying voltage that oscillates in a time varying manner between at least two voltage levels of any polarity. By "high power alternating voltage power supply" is meant a power supply capable of delivering 3kW to 40kW or more preferably 5kW-40kW.

It is desirable that the electric fields between each pair of neighbouring stunning electrodes is alternating and of predefined voltage and frequency as it is this alternating field which induces a stunning seizure in the fish to render them unconscious swiftly and humanely.

Referring now to the figures, it can be seen from Figures 2 to 1 1 that a high power alternating voltage power supply 70, 170 may be powered by single phase or triple phase supply and may comprise 1 , 2 or 3 transformers and/or a power inverter module (preferably configurable) for delivering specific predetermined voltages and frequencies to the stunning electrodes 10 (1 , 2, 3, 4, 5, etc.). Whilst only 5 stunning electrodes are shown, the principles of the present invention can be extend to 6, 7 or more stunning electrodes to ensure sufficient stun over longer distances.

By providing a stunner tube 90 comprising an elongate tube 42 (even when circuitously arranged in loops) and annular stunning electrodes disposed therealong, alternating electric fields can be provided which have electric field lines substantially evenly and symmetrically dispersed across the tube so that fish are within the presence of the electric field no matter their location with respect to the side walls of the tube.

Preferably the stunning electrodes are arranged into a stun station 60 comprising at least two stunning electrodes and a stun maintenance station 62 comprising at least two or three or more stunning electrodes. Typically, one electrode (e.g. electrode 2) is common between the stun station and the stun maintenance station 62.

Typically, the first stunning electrode (e.g. electrode 1 connected to the power supply 70, 170 in the stunner tube 90) is the first electrode in the fish stunner e.g., the first electrode in the elongate tube (in the direction of water flow). However, one or more further electrodes (not shown) may be provided upstream of the first stunning electrode 1 may be provided. This may be connected to ground.

Similarly, the last stunning electrode (e.g. electrode 3, 4 or 5 connected to the power supply 70, 170 in the stunner tube 90) is the last electrode in the fish stunner e.g., the last electrode in the elongate tube (in the direction of water flow). However, one or more further electrodes (not shown) may be provided downstream and may be connected to ground. These further electrodes, typically not connected directly to the power supply, may be provided to sweep up any stray currents.

Turning to the drawings in more detail now, in Figure 2, a flow-through fish stunner apparatus 32 is shown. This stunner apparatus 32 comprises a three phase transformer, adapted to receive power from a three phase supply, two conductors 54 (54A, 54B), an elongate tube 42 having spaced electrode housings 44 spaced there along with individual stunning electrodes 1 , 2, 3 located within and form an electrified stunner tube 90. In this case, a fish pump 24 delivers transport water and fish (not shown) in direction 200 into the entrance of tube 42 passing first electrode 1 and electrode 2 and electrode 3 before exiting the elongate tube 42 into a de-waterer 36 and on to further processing. Typically, this further processing may include for smaller fish asphyxiation whilst lying unconscious in ice water whereas larger fish may be bled and gilled. In Figure 2, three stunning electrodes are provided although preferably four or more stunning electrodes are provided. Having four or more stunning electrodes is helpful to provide the required electric fields over the long stunner tubes needed in flow-through designs, but it is problematic to provide alternating electric fields between multiple especially four or more stunning electrodes, e.g. especially when for safety reasons the first and last stunning electrodes connected to the power supply are at Ov.

Particularly in flow through fish stunning apparatus, stunner tube 90 is typically very long, for example over 12m or more preferably over 14m or more preferably over 16m or more preferably over 18m long. The flow of water through stunner tube 90 is typically quite high to ensure that fish cannot swim upstream and escape from the apparatus. Therefore, to ensure sufficient duration within the fish stunner 32, and therefore sufficient time within the stun maintenance fields 64 in stun station 60 and stun maintenance station 62 to ensure unconsciousness, stunner tube 90 is typically much longer than in recirculation fish stunners. In a stun station, a volume of water is provided with a high electric field sufficient to generate rapid onset of insensibility. In a stun maintenance station, a volume of water is provided with an electric field sufficient to maintain insensibility and prolong duration of unconsciousness so that it persists after leaving the electric field (as explained elsewhere herein).

Even for the flow through arrangement a shorter stunner tube may be provided e.g. by removing some of the water before stunning. Preferably, the stunner tube has a minimum length of 5 - 7 m. In a recirculating fish stunner, the stunner tube may be quite a lot shorter.

Preferably, the fish stunner apparatus is arranged to provide from 1 -2s to 30s, preferably 5 to 30 sec of exposure depending on the species and post stun treatment (in the stun maintenance station), so for a water speed range of 1 to 2 m/s, the stunner tube may be 5 m to 60 m. However, preferably, the stunner tube is 5 to 30 m in length. Typically the initial stun rendering the fish unconscious happens within 1 -2s, preferably within 1 s. For various species, preferably the fish stunner apparatus and stunner tube are configured to provide between 12V rms per meter and 800V rms per meter, or more preferably between 15 V rms per meter and 500V rms per meter (from the AC components). Typically, 400V rms per meter may be used.

To extend the stun duration or increase the field, shorter distances between the stunning electrodes may be used and/or a slower water flow and/or a longer stunner tube (using more pipes or more conjoined pipe sections).

In the stun station 60, high fields of up to 500 or up to 800 V/m may be required with the aim to expose the fish to this for only 1 or 2 seconds and then the field strength may be reduced by a factor of 2 or 3 (preferably not more than 3) in the stun maintenance station 62. The stun maintenance station may have 1 , 2, 3, or 4 or more of these longer tubes (e.g. 42 optionally lengths of pipe) to make up the remaining length of stunner tube 90.

In one example, 400V rms over the first 3m may be provided, then three more lengths of 9m each offering 400V rms along the 9m length (400V/9m). The total stunner tube length would be 30m.

In another example, 600V over the first 1 .2m may be provided followed by 3 lengths of about 3m also with 600V rms along each 3m length. The total stunner length may be 10.2m.

In another example, 80V rms over the first 4m may be provided and then 1 or 3 more lengths of 8 to 10m with 80V rms along each 8 or 10m length. The total stunner length may be 12m or 28m or 13m or 31 m or 14 or 34m or even 15m or 35m or preferably 12m or 14m or 28m or 34m.

Whilst less, preferred, in one particular embodiment, stunning in stun station 60 can take place in water, and stun maintenance in stun maintenance station 62 could take place in air (after passing a dewatering) station.

Additional or alternative transport means (to water), such as a conveyer belt, may be provided in, for example, the stun maintenance and/or stun maintenance station to co-operate with stunner tube 90 for transporting fish within it. Thus, whilst flow-through fish stunners may typically use water alone for transporting fish, some embodiments (e.g. for flat fish) may use a conveyer belt as an alternative or in addition to water as a transport medium. For flow-through fish stunners, the fish are transported through it in flowing water and water is not recirculated. For flat fish, the stun and maintenance section, or just the stun section, would typically be provided in a fish passage (e.g. stunner tube 90) with a conveyor belt lying in slower flowing electrified water.

In Figure 2, a three phase supply 46 is converted by power supply 70 comprising a three phase transformer 48 into two voltage lines namely conductors 54A and 54B. Conductor 54A powers a first group of stunning electrodes, here the first and last stunning electrodes 1 and 3, of stunner tube 90. Conductor 54B powers a middle electrode 2 at a varying alternating voltage V. Thus, first and last stunning electrodes 1 and 3 are held at zero volts and middle electrode 2 varies in a predetermined alternating manner (peak voltage and/or rms voltage and/or waveform and/or frequency) depending upon the species of fish to be stunned. It is preferred that first and last stunning electrodes in the direction of flow are held at Ov. Optionally, the first and last stunning electrodes are substantially at or very near to (<0.5m) to the end of the elongate tube 42. Alternatively, the first and last stunning electrodes are spaced apart from the entrance and exit of the elongate tube 42. The stunner tube 90 comprises that part of the elongate tube 42 that is provided with stunning electric field(s). Elongate tube 42 may extend beyond stunner tube 90. Elongate tube 42 may comprise one or more non- stunning electrodes (not shown) upstream and/or downstream of and spaced apart from the stunning electrodes. The one or more non-stunning electrode(s) may be attached to ground, so as to stop stray currents e.g. near the open ends of elongate tube 42.

In Figure 3, a stunner tube 90 similar to that shown in the Figure 2 having three stunning electrodes 10 is provided. However, here a single phase supply 50 is converted by a single transformer 52 to provide the required voltage difference. The voltage on one output is set at zero volts by earthing it. This is connected by conductor 54A to the first and last stunning electrodes 1 and 3. The voltage on the other output is connected by conductor 54B to middle electrode 2.

Figures 4, 5A, 5B and 6 to 12 show further embodiments of the invention. In Figure 4, a stunner tube 90 comprising an elongate tube 42 of substantially constant circular cross section is provided between fish pump 24 and dewatering station 36, although as described elsewhere the fish pump may be provided after the fish stunner. Elongate tube 42 may be wound into loops to provide a smaller footprint shown in Figure 1 . Spaced along elongate tube 42 are four stunning electrodes 1 , 2, 3, and 4 housed in electrode housings 44 forming stunner tube 90. A first pair of neighbouring stunning electrodes 1 and 2 forms a stun station 60. These are neighbouring in the direction of flow. Stunning electrodes 1 and 2 are spaced by distance L1 . The last three stunning electrodes 2, 3 and 4 form two pairs of neighbouring stunning electrodes each pair may be spaced at a distance L2. Alternatively, stunning electrodes 2 to 3 may be spaced differently than stunning electrodes 3 to 4. By providing extra tapping in the transformers, different voltages may be provided for use with different spacings of stunning electrodes to produce the same fields, or with the same spacings to produce different fields. Stunning electrodes 2, 3 and 4 provide a stun maintenance station 62. Typically, fish passing through stun station 60 experience a relatively high alternating electric field (voltage gradient) so as to render them immediately unconscious (via an epileptic-type seizure). Stun maintenance station 62 typically provides a lower alternating electric field to maintain the fish in an unconscious state. Typically, the stun maintenance station retains the fish in an unconscious state during their transport through the stun maintenance station 62 but also for a period of time after they exit. This ensures that if fish are subsequently placed in ice water for example they do not regain consciousness before expiring.

By providing stunning electrodes at one or more predetermined but different distances, e.g. L1 and L2, then a more limited number of voltages can be used to provide different electric fields (voltage gradients) along stunner tube 90. As the number of stunning electrodes 10 increases this becomes more important as stunning electrodes can be grouped together (e.g. 1 +3, 1 +3+5, 2+4, 2, 4) to receive particular voltages from particular conductors, but fewer voltages overall are needed to be provided. This facilitates provision of different electric fields in the stun station and in the stun maintenance station without requiring additional voltages to be provided by the power supply as the different physical arrangements if the stun and stun maintenance station allows the voltages to be used in both to provide the desired different electric fields.

In Figure 4, a specially wound three phase transformer 48 provides three voltages to four stunning electrodes. This is achieved by grouping the stunning electrodes; in this case a first group is formed from first and last stunning electrodes 1 and 4 which are held at zero volts. These are preferably near the entrance and exit of the elongate tube 42. Thus, conductors 54A provide zero volts to stunning electrodes 1 and 4. Conductor 54B provides a first alternating voltage V1 to second electrode 2. Conductor 54C provides a second alternating voltage V2 to third electrode 3. Whilst the peak voltages of alternating voltages V1 and V2 may be the same, these are not in phase and therefore there will be a potential difference between stunning electrodes 2 and 3 providing an appropriate alternating electric field for the stun maintenance station. Stunning electrodes 2 and 3 and 3 and 4 may be equally spaced as this is the simplest arrangement or may be differently spaced one from the other (e.g. to provide the same or different electric fields between each pair of neighbouring stunning electrodes). By selection of distances L2 with respect to L1 , lower electric field may be provided between later stunning electrodes 2, 3 and 4 in stun station 62 than between stunning electrodes 1 and 2 in stun station 60. This arrangement advantageously reduces the number of voltages that need to be supplied. A higher alternating electric field can be provided between stunning electrodes 1 and 2 whilst a reduced electric field (voltage gradient) can be provided between stunning electrodes 2 and 3 and 3 and 4 by using similar voltages but extending the length of the section in a predetermined manner. Thus, for particular species and particular flow rates and salinity of water, the distance ratio of L2 to L1 may be predetermined to provide a predetermined ratio of stun station electric field to stun maintenance station electric field.

Figure 5A shows a similar system to that of Figure 4 using a three phase supply and a three phase transformer but providing power to five stunning electrodes 10 (stunning electrodes 1 , 2, 3, 4 and 5). Here, stunning electrodes 10 are formed into three groups, a first group comprising stunning electrodes 1 and 5 held at zero volts and a second group (stunning electrodes 2 and 4) provided with alternating voltage V1 and a third group comprising a single middle electrode 3 held at an alternating voltage V2. Conductors 54A are earthed and provide zero volts to stunning electrodes 1 and 5.

Conductors 54B are common to another phase of the three phase transformer 48 to provide alternating voltage V1 . Finally, conductor 54C is connected to another phase of three phase transformer 48 to provide alternating voltage V2. Stunning electrodes 2, 3, 4 and 5 are equi-spaced at a predetermined distance L3 which is between 1 and 2 times the distance L1 between stunning electrodes 1 and 2. This is unlike Figure 4 in which distance L2 is over twice L1 .

In Figure 5B an alternative arrangement is shown in which only two phases from three phase transformer 48 are used (as in Figure 2) . In this embodiment stunning electrodes 1 , 3 and 5 are grouped together and powered by earthed conductor 54A from one phase of transformer 48 and stunning electrodes 2 and 4 are grouped together and powered at alternating voltage V1 by another phase of three phase transformer 48. Figure 6 shows an alternative embodiment of flow-through fish stunner apparatus 32 comprising two single phase transformers 52 (52A and 52B) and/or stunning electrodes 10 in elongate tube 42 (forming stunner tube 90), stunning electrodes 1 and 2 forming stun station 60 and stunning electrodes 2, 3 and 4 forming stun maintenance station 62. Here, stunning electrodes 2 and 3 are spaced at a distance L4 which is less than a distance L5 between stunning electrodes 3 and 4 although it may be more. Alternatively, stunning electrodes 2, 3 and 4 may be equi-spaced a distance L4. A first single transformer 52A is connected to a single transformer 52B and provides, at a common electrode, an earthed conductor 54A for first and last stunning electrodes 1 and 4. Second electrode 2 is powered by the other phase from first transformer 52A via conductor 54B. A third electrode 3 is powered by the other phase of second single phase transformer 52B via conductor 54. Thus, stunning electrodes 2 and 3 are at respective alternating voltages V1 and V2 which may have similar peak voltages but which are out of phase with respect to one another.

Figure 7 shows a three phase supply being used to power a flow-through fish stunner apparatus 32 comprising two single phase transformers 52A and 52B. Here, first, third and last electrode 1 , 3 and 5 are connected to a common conductor from first and second transformer 52A and 52B and are held at zero volts. The other phase of first single phase transformer 52A powers second electrode 2 at first alternating voltage V1 , and the other phase of second single phase transformer 52B provides second alternating voltage V2 to electrode 4. Voltages V1 and V2 may have the same or similar, or indeed different, peak voltages but in any case are out of phase with one another thereby providing alternating electric fields in the corresponding section of stunner tube 90.

Figure 8 shows a flow-through fish stunner comprising a single phase transformer 52 powered by a single phase supply 50 delivering power to five stunning electrodes 1 , 2, 3, 4 and 5. A first group of conductors 1 , 3 and 5 are connected together to one end of transformer 52 by conductors 54A and are grounded at zero volts. The other end of transformer 52 is connected to a second group of stunning electrodes 2 and 4 by conductors 54B and are provided with a predetermined alternating voltage V. Different alternating electric fields are provided in stun station 60 and stun maintenance station 62 by stunning electrodes 1 and 2 being differently (more closely) spaced than stunning electrodes 2, 3, 4 and 5. A variable voltage may be provided by providing an alternate or variable voltage tap via conductor 154B or multiple taps on the transformer may be provided to offer a variety of voltages.

Figure 9 shows further alternative arrangements for a transformer based solution of a flow-through fish stunner apparatus 32. Here, apparatus 32 comprises two single phase transformers 52A and 52B connected to a single phase supply 50 and arranged to power five electrode stunner tube 90.

Conductors 54A are provided grouping stunning electrodes 1 , 3 and 5 to a common ground between first and second single phase transformers 52A and 52B. The other phase of 52A is connected to electrode 2 to provide a first alternating voltage V1 . The other phase of second single phase transformer 52B is connected to fourth electrode 4 by conductor 54C to provide a second alternating voltage V2. The arrangements described above provide the ability to offer bespoke solutions for particular species of fish and salinities (conductivities of water) by varying one or more of the power supplied, and/or the distances between stunning electrodes in the stun station, and/or the distance between one or more pairs of neighbouring stunning electrodes in the stun maintenance station, and/or the separation of stunning electrodes in the stun station with respect to separation of stunning electrodes in the stun maintenance station 62.

For illustration purposes, examples of field lines 64 developed between neighbouring stunning electrodes are shown in Figure 10. Here, five annular stunning electrodes are shown. Electrode 1 has one neighbouring electrode. Electrode 2 has two neighbouring stunning electrodes that is electrode 1 and electrode 3. Electrode 3 similarly has two neighbouring stunning electrodes that is electrode 2 and electrode 4. Electric field lines 64 are substantially continuous and substantially longitudinally arranged along elongate tube 42 of stunner tube 90. Furthermore, the annular nature of stunning electrodes 10 (1 , 2, 3, 4 and 5) ensure that the electric field is substantially symmetrical (about a central longitudinal axis) and substantially evenly distributed across the cross section of elongate tube 42 through which water and fish pass.

Single phase power: Where single phase power is available one or two single phase transformers can be used with a single phase supply to provide the required voltage steps for the species of interest. Single phase ac power comprises a pair of conductors where the voltage of one conductors oscillates from +310 to -310 V relative to the other (assuming normal 220 V rms power). By setting the voltage of one of these conductors to zero the other is forced to oscillate between +310 and -310 [N.B.220 x V2 = 310].

One or more embodiments of the present invention uses a stun tube with an odd number of stunning electrodes, the first and the last connected Ov and the middle one connected to the oscillating voltage (when the number of stunning electrodes = 3, 7, 1 1 , etc.) or to Ov (zero volts) (when the number of stunning electrodes = 5, 9, 13, etc.). Therefore at the start of the tube, between the outside world and the 0 V electrode there is no voltage gradient (electric field). This is therefore safer.

Between the first and the second stunning electrodes the voltage rises from 0 V to the voltage of the second electrode. There is therefore a voltage gradient between these two. Between the second to last and last stunning electrodes the voltage drops from the oscillating voltage back to 0 V. There is therefore a voltage gradient between these two. Between the last electrode and the end of the tube which is at 0 V there is no voltage gradient. This is therefore safer. To make the system longer, two more stunning electrodes can be added. The second to last electrode is again at the osculating voltage and the first and last stunning electrode(s) are preferably at 0 volts.

Three Phase Power: Where three phase power is available three phase transformer or two single phase transformers can be used with a triple phase supply to provide the required voltage. In three phase power systems there are 4 conductors, one of which is set to 0 V and the other three that all carry an oscillating voltage as with single phase. However the voltages of these three conductors reach +310 and -310 v at different times. They are each separated by a phase lag of 120 degrees. This means that while there is a voltage difference of between +310 and -310 v between any one of them and the 0 v conductor, there is also a voltage difference between any two of the three power conductors which oscillates between +538 and -538 V [N.B. 220 x V2 x V3 = 538]. In this

implementation, it is possible therefore to have a first and last stunning electrode set at 0 V and then any number of intermediate stunning electrodes attached to the other three conductors ensuring that no two adjacent stunning electrodes are attached to the same conductor (otherwise their voltage is the same and so voltage gradient between them is zero).

Using transformers is a very simple way to achieve the "power" required on the stunning electrodes for a narrow and precise set of parameters - but it is not very flexible. In an example embodiment of a further aspect, a highly flexible alternative is provided (see Figure 1 1) which uses switches (e.g. IGBT (insulated-gate bipolar transistors) or MOSFET switches) to provide pulse width modulation to create precise electrical waveforms in which all aspects of the waveform, voltage and frequency can be adjusted.

Preferably, in both approaches, feedback for conductivity changes, and/or density or crowding of fish in the tube, and/or change of flow rate, can be used to adjust the alternating voltage output e.g. on the fly during processing. Thus, preferably monitoring in real time is provided and the power supply can make the adjustments accordingly, either automatically (e.g. in during the next offline period or more preferably in real time e.g. within 30 seconds), or manually (e.g. during set -up). Typically the transformer power supply would be switched off, adjusted and switched on again.

Turning now to Figure 1 1 , another aspect of the invention is shown. Here a configurable high power alternating voltage power supply 170 is shown. The configurable high power alternating voltage power supply 170 has been designed to be configurable to provide varying alternating voltages of one or more required parameters (peak voltage, rms voltage, frequency, waveform etc.) for use in stunning e.g. a flow through fish stunner for particular species in salt (typically >50000μ5/ατι conductivity) and/or fresh water (typically δθμε/ατι to more brackish Ι ΟΟΟμε/αη). Typically, power supply 170 will be capable of providing up to 14 or even 16kW or more but in another embodiment at least 5kW or at least 7kW or at least 10kW or indeed 12kW may be provided. Whilst this is less desirable, one or more configurable high power alternating voltage power supplies 170 may be provided.

Configurable power supply 170 comprises an AC protection control module 172, an AC-DC rectifier module 174, an isolated DC-DC converter 176, an output inverter module 178 (converting DC to AC) and a control module 180. Control module provides overall control but local control is typically pushed down to individual modules 172, 174, 176 and 178.

AC protection and control module 172 provides front end power correction and safety features for connecting to mains grid AC power supply (not shown). This module delivers an appropriate AC supply to AC-DC rectifier module 174. Most of the protection and control is provided by module 172 on the AC input side of AC-DC rectifier module 174. A 15kW system with PFC will require around 16 to 17kVA of power supply capability. AC and protection module 172 and AC-DC Rectifier module 174 may be provided by a single module (not shown) e.g. on a single PCB.

AC-DC rectifier module 174 functions as an active front end to provide an adjustable, stabilised DC output with a very high power factor on the AC input side. Typically this is configured to convert a preselected mains supply (or more than one mains supply by swapping in and out modules 172 or providing a configurable input module 172 (e.g. 230 or 1 10 V 50 or 60 Hz input) into DC using a full wave rectifier. AC-DC rectifier module 174 (module A) may also provide an isolated DC supply to power the control system 180 (module D) as well as providing a DC link voltage to power DC to DC converter 176 (module B).

Module 176 is an isolated DC-DC converter to step up the voltage. The DC from module 174 is chopped into AC using switches to enable use of a transformer to increase the voltage. Then a DC bridge is provided on the secondary side of the transformer to produce high voltage DC. The high voltage DC (here 600V DC) is provided to output inverter module 178. Module 176 functions as an intermediate line converter to provide isolation from input to output so as to allow for a fully floating output stage minimising the risk of electric shock and unwanted earth currents. The output system may need to have one side tied to earth and galvanic isolation between the three phase AC input and the output of this module is virtually a necessity. Module 176 may be based on phase shifted full bridge topology for a high power, high voltage isolated converter. Isolated DC-DC converter module 176 may comprise one, two or more converters e.g. two 8kW converters running in parallel to provide full 16kW capability. For example, the primary side of each converter may comprise a full bridge on the primary side and a bridge rectifier on the secondary side which allows the transformer to use a single secondary winding. The converter bridge on the primary side typically may comprise MOSFETs and IGBTs. The secondary side may comprise a bridge rectifier. Isolated DC-DC converter 176 provides an isolated/regulated 600Vdc DC link to feed the output inverter stage.

A preferably configurable output inverter module 178 is provided at the output of the DC-DC converter module 176. The high voltage DC power (e.g. 600V) provided to an input of inverter module 178 is chopped into AC using further switches (such as MOSFETs or IGBTs) to create pulses and so form desired waveforms at at least one alternating voltage. Where one alternating voltage is provided this can be used (in the same way as the embodiments in Figures 2 to 12 with two conductors) in combination with a stun tube 90 and stunning electrodes 10, typically at predetermined distances along the tube, to provide the alternating electric field necessary to stun and preferably also maintain stun in particular species.

Thus, the function of the output inverter module 178 is to use the high voltage (e.g. approx. 600V) isolated DC link from module B (isolated DC to DC converter module 176) to create the custom output power profiles required typically using PWM techniques. The inverter output module 178 voltage will be controlled using closed loop digital control. Users will be able select pre-programmed parameters for particular species by selection of suitable control switches (not shown) which will be configured to arrange for delivery of pre-selected program parameters e.g. AC voltage output, and/or output frequency, which the inverter module 178 will then produce. The preferred wave forms include AC or pulsed DC with frequencies e.g. from 5Hz to 1000Hz or up to 2000Hz or even 10,000Hz and preferably around 125Hz or more preferably <125Hz e.g. 10 to 50Hz or 20 to 40Hz or 10Hz or 20Hz or 25Hz or 40Hz or 50Hz. The shape may be sinusoidal, square, smooth square or quasi-square wave. The maximum peak voltage developed across the output is 600V (limited by the DC link input voltage). The maximum average output power is around 14kW. The output RMF load current is typically a maximum of 50A _rm s.

Output inverter module 178 (module C) typically will keep the pulse width modulation (PWM) generation local to the power devices to avoid noise. Control of the system is preferably managed by control module 180 (module D) which will communicate via a bus (CANBUS). Preferably, all the inverter timing critical low level control and protection may be done directly on inverter module 178 (module C) with slower high level communications to the control system over CANBUS. All monitoring may be performed locally and then sent digitally to the host control module 180. Anticipating EMI at such voltage levels, to avoid noise, lower power control electronics will preferably all sit on one PCB. Control Module 180 (module D) will provide higher level control of the whole system and interface to the user interface front end (not shown).

Example wave forms that might be provided by high power alternating voltage power sources 70 in Figures 2 to 10 or using the configurable high power alternating voltage power source 170 of Figure 1 1 are shown in Figures 12A and 12B. In Figures 12A and 12B alternating voltage wave forms that may provide voltages V, V1 and V2 in Figures 2 to 1 1 are shown for saltwater species and fresh water species. Use of the quasi-square wave simulation may reduce the power demands on the system. Preferably the output impedance of the power supply 70, 170 is continuously monitored to provide feedback on the variation of the conductivity in the stunner tube 90.

In the present invention the inventor(s) propose two alternative approaches to developing a suitable high voltage power supply for the present invention, one series of embodiments generates narrow voltages and frequencies at high power (e.g. around 5 to 40kW, ) (see power supply 70), the other series of embodiments generating highly flexible control on the output at high power (see power supply 170 in Figure 1 1). Both approaches can be assisted by careful consideration of electrode design (size, shape, location), electrode spacing along the tube and electrode voltages required for the particular application.

In one example embodiment of the first approach, one or more single phase or three phase transformers are used to generate precise parameters (e.g. voltages) alternating between the first two stunning electrodes which are of known spacing and the lower parameters (e.g. voltages) in the remaining stunning electrodes which are also of known (usually larger) spacing. In one example embodiment a three phase transformer is used to give an isolated supply at the required voltage. In one example embodiment, the high voltage power supply is powered from single phase 230 Volt supply to provide a sine output of 5Hz to 10,000Hz or 5Hz to 2000Hz, or 5Hz to 1000Hz, or 125Hz to 1000Hz or as described elsewhere herein. As far as the present inventor(s) are aware a large transformer has never been used to generate a stunner for fish. Care is needed to ensure safety at these levels.

In an example embodiment of the second approach (see Figure 1 1). a new electronics arrangement in a newly designed configurable high power alternating voltage power supply is used to generate flexible control of voltage, waveform, and frequency. All controls and choices have implications for fish quality.

Input power supply: In at least one embodiment the present invention include options for operation on single phase 220/240 V operation; three phase 200 V; or three phase 380/415 V. 50 Hz or 60 Hz may be encountered. The unit may be operated from a generator so a stable voltage cannot be relied on.

Output: Whilst one preferred example embodiment uses alternating voltage at frequency 125 ± 5 Hz, other embodiments using other frequencies can be envisaged including the option to select a few other frequencies such as a e.g. 5Hz, 10Hz, 20Hz, 25Hz, 20 to 40Hz, 10 to 50Hz, 50Hz, 125Hz, 100 Hz, 300 Hz, 600 Hz and 1000 Hz is of interest or as described elsewhere herein.

In one example embodiment, the configurable high power alternating voltage power supply is capable of supplying maximum rms voltage of 600 V, a minimum rms voltage of 50 V, a maximum rms current of 50 A, and a maximum power of 15 kW. The expected load is resistive with a minimum 2.5 ohms and the output is to be floating or to have one pole tied to earth.

Control: The voltage to be generated is determined by parameters set before start up and may be modified by the output impedance (e.g. at the low end of the conductivity range for fresh or brackish water due to changes in conductivity of water and/or the number and/or clustering of fish, and/or for all water conductivities due to changes in volume of water) which may be continuously monitored. For example the output impedance across the stunning electrodes may be measured (e.g. 1 -2, 3-4 etc.) e.g. by measuring the voltage and knowing the current and the geometry, the impedance can be deduced. Nevertheless, it is not expected for saltwater in particular (with such high conductivity) that other factors will have any significant influence on conductivity requiring changes to be made during processing. The delivered voltage is preferably within 5% of the target voltage to ensure fish are appropriately stunned according to their species specific requirements. Following start up or changes to the impedance, the target voltage should be achieved within a short predetermined time e.g. 30 seconds. Impedance feedback is provided by measuring impedance directly across the stunning electrodes and/or by measuring conductivity and/or salinity, and feeding this to the control module. Preferably for the configurable approach at least, feedback on conductivity and flow rate is ongoing during operation, whereas for the transformer configuration these (conductivity and flow rate) may be manually measured and/or configured at set up so that appropriate electric fields are delivered for the species of interest under these conditions.

A user interface (not shown) is typically provided to enable the device to be started, stopped and controlled from a purpose built microprocessor based control unit. This facilitates basic system monitoring functions including voltage, current, electronic component temperature and reason for system emergency shut down.

In one aspect the present invention provides fish stunner apparatus and methods for particular use in stunning in a flow through fish stunner apparatus using saltwater. In further aspects the present invention provides bespoke high power alternating power supplies and configurable high power alternating power supplies for use in such fish stunners and methods of fish stunning.

By providing a high power system optionally configurable to different mains and/or optionally configurable to deliver different species specific voltage parameters e.g. for use in flow through saltwater systems, a more humane approach to fish harvesting is possible in a wider range of locations (e.g. loch side), with reduced handling, with a wider range of species in a wider range of water types (e.g. fresh water, or preferably saltwater- from salty brackish water, saline water and brine). Feedback measurements of water salinity either directly or via output impedance coupled with a configurable power supply capable of varying output voltage(s) relatively rapidly (within around 30s) can facilitate more continuous operation. The use of feedback can also assist so that preferably the voltage to be generated is continuously monitored and adjusted (e.g. adjusting one or more of peak voltage, rms voltage, waveform shape, frequency, AC content, ) to enable species specific electric fields to be maintained in the stunner tube during operation, e.g. to compensate for changes in conductivity and rate of flow of the fish transport medium (water).

High power means relatively high power of 5- 40kW or 4-25kW or 7kW-20kW or as described elsewhere herein typical voltage range of up to 1000V or more likely up to 800V or 600V. The frequency of the alternating voltage may be 5 -10,000Hz or 5-2000Hz or as described elsewhere herein.

Other embodiments will be apparent to those skilled in the art from the information contained herein and any feature from any embodiment of any aspect of the invention can be combined with any features from any other embodiment of any aspect of the invention as would be understand by a person skilled in the art from this disclosure.