Abstract:
A device for stunning fish comprising: an elongate member comprising an open channel through which a fish can pass; a pneumatically operated gun pivotally mounted in said channel, said gun comprising an impact cylinder and piston, wherein said piston is connected to a cylinder striker which is retractably extendable from a sleeve on said cylinder, and wherein said gun can pivot between a lowered firing position where said striker can stun said fish at a set point in a channel and a raised position where said fish can pass beneath said gun; a vertical guide plate pivotally mounted on the internal surface of each wall of said channel and having extended (outward) and retaracted (inward) positions, wherein the end of a guide plate distal the pivotal mounting is at or near said set point and the pivotal mounting is between said set point and the channel entry; a mechanism for pivoting said gun between said lowed and raised positions; a mechanism for pivoting each said guide plate between said extended and retracted positions; a trigger for firing said gun when said lowered position and activating said pivot mechanism to pivot said gun to said raised position, and activating said guide plate pivot mechanism to pivot said plates to said retracted position; and a sensor for detecting passage of said fish out of said channel and activating said pivot mechanism to return said gun to said lowered position, and activating said guide plate pivot mechanism to pivot said plates to said extended position.

Description:
TECHNICAL FIELD  
       [0001]     The invention described herein relates to devices and methods for stunning fish. In particular, the invention is directed to a device and method for the automated stunning of fish although the scope of the invention is not necessarily limited thereto.  
       BACKGROUND ART  
       [0002]     Processing of animals for food usually involves the initial slaughter of the animal. In the processing of larger animals such as cattle, this is typically done by a blow to an animal&#39;s head using a pneumatically- or cartridge-powered gun with a captive bolt or piston in place of a projectile.  
         [0003]     Processing of some fishes also requires slaughter as an initial step in the process. For example, salmon are typically “stunned” by a blow to the head before processing as food. In many instances, the blow is applied with a simple club, there being no readily available apparatus for the procedure.  
         [0004]     Any apparatus must be capable of delivering a blow to the head of fish in such a way that stunning can be done humanely. For most processing needs, the apparatus must also be capable of delivering blows quickly and repetitively so that large numbers of animals or fish can be processed.  
         [0005]     Pneumatically powered apparatus are used for larger animals because they meet the needs set out in the previous paragraph However, such apparatus are not suitable for use with smaller animals or fish. Smaller hand-held pneumatic devices are known—for example, pneumatically powered nail guns—but these are not suitable for use as a fish or animal stunning device because of their configurations. Such devices are nevertheless capable of delivering an adequate force.  
         [0006]     A pneumatically-powered device suitable for stunning small animals and fish is described in International Application No. PCT/AU01/00745 (Publication No. WO 01/97621) by the present applicant. While this device can be efficiently used for the stunning of large numbers of fish, it has the limitation that it cannot be used in an automatic, flow-through fashion as each fish has to be presented to the device manually.  
         [0007]     It is an aim of the invention to provide a stunning device which can be used in an automated-manner or at least provide the consumer with a useful choice.  
       SUMMARY OF THE INVENTION  
       [0008]     In a broad format, the invention provides a device for stunning fish, the device comprising:  
         [0009]     an elongate member comprising an open channel through which a fish can pass;  
         [0010]     a pneumatically-operated gun pivotally mounted in said channel, the gun comprising an impact cylinder and piston, wherein the piston is connected to a cylindrical striker which is retractably extendable from a sleeve on said cylinder, and wherein said gun can pivot between a lowered firing position where said striker can stun said fish at a set point in said channel and a raised position where-said fish can pass beneath the gun;  
         [0011]     a vertical guide plate pivotally mounted on the internal surface of each wall of the channel and having extended (outward) and retracted (inward) positions, wherein the end of a guide plate distal the pivotal mounting is at or near the set point and the pivotal mounting is between the set point and the channel entry;  
         [0012]     a mechanism for pivoting said gun between said lowered and raised positions;  
         [0013]     a mechanism for pivoting each said guide plate between said extended and retracted positions;  
         [0014]     a trigger for firing said gun when in the lowered position and activating said pivot mechanism to pivot said gun to the raised position, and activating said guide plate pivot mechanism to pivot said plates to the retracted position; and  
         [0015]     a sensor for detecting passage of said fish out of said channel and activating said pivot mechanism to return said gun to the lowered position, and activating said guide plate pivot mechanism to pivot said plates to the extended position.  
         [0016]     The operating principle of the stunning device according to the invention is similar to that of the WO 01/97621 device in that the fish is killed by a blow to the head administered by the piston of the gun. Activation of the piston results from the head of the fish contacting the trigger. The trigger and cylinder are configured such that when the piston is activated, it strikes the fish just behind and/or between the eyes. This impact is sufficient to kill the fish due to the shock to the brain. However, the device according to the present invention differs substantially from the WO 01/97621 device in that with the former device, the fish passes through the device rather than having to be manually inserted into and withdrawn from the device.  
         [0017]     With regard to the components of the device, the channel typically comprises sheets of material forming the walls and floor of the same. Cross-pieces can be provided along the open (top) side of the channel plus strengthening members where device components are mounted to the channel.  
         [0018]     The pivoting of the gun is typically effected by providing a mounting for the gun which is connected to the channel at an appropriate point by a shaft which spans the channel walls. The pivot mechanism is advantageously associated with the gun mounting. For example, a crank can be provided on the shaft of the mounting to which crank a pneumatic ram is connected. Any means of pivoting the gun can be employed however.  
         [0019]     The trigger typically comprises a contact plate having at least one micro-switch associated therewith. The contact plate is contacted by the nose of the fish when at the set point while the at least one micro-switch activates the gun and the pivot mechanism.  
         [0020]     It will be appreciated that guide plates—which, as a consequence of being on opposite sides of the channel, in effect form a chute—aid presentation of the fish to the gun in that they maintain the verticality and centrality of the fish. The mechanism for pivoting the guide plates can be an integral part of, or at least associated with, the gun pivot mechanism, or can be a separate mechanism.  
         [0021]     The sensor for detecting passage of the fish out of the channel can be any sensor which will respond to movement of the fish through the sensor point. However, for consistency with other aspects of the devices to be described below, the sensor is advantageously a gate or flap which pivots upwardly when contacted by the fish. This pivoting signals the gun pivot mechanism to return to the lowered (firing) position.  
         [0022]     A device according to the invention can also include a lateral and upwardly angled plate which is abutted by the chin of the fish when at the set point. To allow passage of the fish past the set point after firing of the gun, the plate can pivot between raised and lowered positions. In the raised position, the plate supports the chin of the fish while in the lowered position, the plate rests flat against the floor of the channel allowing the fish to be carried on through the channel.  
         [0023]     A mechanism is provided for pivoting the chin plate between the raised and lowered positions. Like the guide plate pivot mechanism, the chin plate pivot mechanism can be an integral part of, or at least associated with, the gun pivot mechanism.  
         [0024]     The device of the invention can optionally include an entry control module. This module includes an entry sensor that permits only one fish at a time to be at the set point or approaching the set point. The module either has its own channel which is connected to the entry of the device channel or can be mounted into an extended device channel.  
         [0025]     The entry control module principally comprises at least one gate or flap pivotally mounted at the top of the channel at or near the mouth thereof. The gate can sense the presence of a fish in the device at or near the set point. On sensing a fish, the gate is locked thereby preventing entry of a further fish. Sensing of the exiting of the fish that has just been stunned results in the unlocking of the entry control module so that the next fish can enter the device and advance to the set point.  
         [0026]     The elements and operation of the entry control module will be explained in greater detail below.  
         [0027]     It will be appreciated by one of skill in the art that the various mechanisms of a device according to the invention can be operated by any suitable means. Typically however, mechanisms are pneumatically operated in the same manner as the gun. Control of mechanisms is also typically pneumatic.  
         [0028]     Other features of a device will be detailed in the following exemplification of a device as will the operation of the device. Briefly however, devices according to the invention can be operated in “hands on” and “hands off” modes. In the former case, an entry control module is not required and an operator merely places fish, individually, into the channel of a device. The operator will of course await the exit of a stunned fish before presenting a further fish to the device.  
         [0029]     Inclusion of an entry control module allows operation of a device in a “hands off” manner. However, to facilitate such an automatic operation of the device, a chute is generally provided so that fish are presented to the mouth of the entry control module channel one at a time. Inclusion of an entry control module also ensures that every fish which passes through the device is stunned.  
         [0030]     Passage of fish through a device does not require a earner fluid as mucous on the surface of a fish acts as a lubricant. However, a stream of water passing through the device—which may occur during automated operation when a chute supplies fish to the device—does not adversely effect operation of the device provided that the stream does not interfere with sensor function.  
         [0031]     Since gravity provides the energy for movement of the fish through the channel, tilting of the channel downwardly from mouth to exit is advantageous. Preferably, the device is tilted at an angle of at least 3°.  
         [0032]     Components of the device can be manufactured from any suitable material but are typically manufactured from metals, or plastics where the latter is more appropriate. Preferred metals are stainless steel and brass. Stainless steel components are preferably electro-polished to provide superior corrosion resistance.  
         [0033]     Devices according to the invention can be conveniently used with fish of commercial weight such as salmon, trout and sea bass. Devices are most particularly suited for the stunning of salmon during the commercial processing thereof.  
         [0034]     With devices according to the invention, fish to be processed can be rapidly and efficiently stunned with minimal risk of injury to an operator since operation of devices can be automated. An additional advantage of devices according to the invention is that the external appearance of the animal or fish is not affected by the killing process. This is particularly important for sale of whole fish. The quality of fish is also enhanced through more rapid and humane killing at the point of harvest.  
         [0035]     In order that the invention may be more readily understood and put into practice, one or more preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]      FIG. 1  is a perspective side view of a device according to the invention.  
         [0037]      FIG. 2  is a further perspective view of the device shown in  FIG. 1  in which the opposite side of the pneumatic gun can be seen including the gun trigger.  
         [0038]      FIG. 3  is a perspective view from above of the device of  FIG. 1  in which the gun assembly mounting can be seen in greater detail.  
         [0039]      FIG. 4  is a perspective view of the device of  FIG. 1  from the entry end of the channel in which a guide plate and its pivot mechanism are visible.  
         [0040]      FIG. 5  is a further perspective view of the device of  FIG. 1  from the entry end of the channel in which a chin plate and its pivot mechanism is visible.  
         [0041]      FIG. 6  is a perspective view of the gun trigger.  
         [0042]      FIG. 7  is a perspective view of the device exit sensor.  
         [0043]      FIG. 8  is a perspective view from above of the entry sensor module.  
         [0044]      FIG. 9  is a perspective view of the entry sensor flap control switch activator.  
         [0045]      FIG. 10  is a schematic representation of the pneumatic control circuit of the exemplified device.  
         [0046]      FIG. 11  is a perspective close-up view of a variant of the device exit sensor showing detail of the sensor valve.  
         [0047]      FIG. 12  is a partial perspective view of the exit sensor showing optional components associated with the sensor flap. 
     
    
       [0048]     For simplicity, air supply lines have been omitted from the drawings showing the device and device components. In drawings showing particular device components other components have been omitted for clarity.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0049]     The device to be described in the following paragraphs includes the optional entry control module. It will be appreciated however that inclusion of this module is not an essential component of the invention.  
         [0050]     With reference to  FIG. 1 , there is shown device  1  comprising channel  2 , gun assembly  3 , and exist sensor  4 . An entry sensor module  5 , not shown in the drawing but to be described below, is fitted at the mouth of channel  2 . Gun  3  is shown in the raised position—that is, post firing. Proximal side wall  6  of channel  2  can be seen in the drawing.  
         [0051]     Gun assembly  3  has an impact cylinder  7  and a sleeve  8  from which a striker extends (see below) for stunning a fish on firing. The assembly is pivotally mounted to a shaft  9  across channel  2  by a pair of rails  10  and  11 . Pivoting is effected by a double-acting pneumatic ram  12  which is connected between a crank  13  associated with rail  10  and an arm  14  pivotally connected to a plate on side wall  6 . The position of arm  14 —and hence the position of the gun piston at firing—is set by an adjusting screw  15  between distal end  16  of arm  14  and a fixed member  17  extending upwardly from side wall  6 .  
         [0052]     The other components of device  1  referred to above will be described in greater detail below.  
         [0053]     The reverse side of gun assembly  3  as visible in  FIG. 1  is shown in  FIG. 2 . Rails  10  and  11  of the pivotal mounting of the gun can between. A trigger assembly  18  is pivotally mounted to the rails. This assembly includes a contact plate  19  which is pivotal within the assembly and an arm  20  to which trigger valves are mounted. The last mentioned and other components of the trigger will be described below.  
         [0054]     Striker  21  can be seen extending from sleeve  8  of gun assembly  3  in  FIG. 2 . The position of contact plate  19  relative to striker  21  can be set by an adjusting screw  22  between an end  23  of trigger assembly  18  distal the contact plate and an arm  24  on rail  11 .  
         [0055]     Elements of the device for effecting pivoting of the pair of guide plates (see  FIG. 4 ) and chin plate (see  FIG. 5 ) present in the device can be appreciated from  FIG. 3 . A shaft  25  is provided across rails  10  and  11 . The ends of shaft  25  are located in slots in the ends of links  26  and  27  to the chin plate. (The slots allow for the variable positions of rails  10  and  11  with adjustment of gun assembly  3 .) Springs  28  and  29  are connected between a point on links  26  and  27 , respectively, to a second shaft  30  spanning rails  10  and  11 . These springs bias the chin plate downwards to the ready to fire position and override the play resulting from the slots in the ends of links  26  and  27 .  
         [0056]     Springs  31  and  32  on shaft  9  counterbalance the weight of gun assembly  3 . Ends  33  and  34  of shafts on guide plates within channel  2  (see  FIG. 1  and the description of  FIG. 4  to follow) are also visible in  FIG. 3 , these being journalled to bearings  35  and  36  at the top of the channel and bearings in the floor of the channel (not visible in the figure).  
         [0057]     One of the guide plates of the pair of plates referred to above is visible in  FIG. 4 . Guide plate  37  is connected to shaft  38  which is journalled to bearing  35  (see also  FIG. 3 ) and bearing  39 . A crank  40  on shaft  38  is pivotally linked to a crank  41  on shaft  9  of the gun assembly pivot (see  FIG. 1 ) by a coupling  42 . A spring  43  is also provided to bias guide plate  37  to the outward position. Guide plate  37  when in the inward position, in conjunction with the opposite guide plate, holds the fish upright and centrally as it approaches the gun assembly for firing of the gun.  
         [0058]     The operation of a guide plate is as follows. On pivoting upward of the gun assembly after firing; shaft  38  is rotated by the linkage to the gun assembly via coupling  42  and cranks  40  and  41 . The rotation of shaft  38  thus also rotates guide plate  37  until it lies close to parallel with side wall  6  of the channel of the device. Pivoting of the gun assembly to the lowered (firing) position forces the guide plate to return to its inward position. The guide plate opposite to guide plate  37  operates in an identical manner. Adjustment of the distance between the ends of the guide plates distal their shafts is effected by a screw  44  which sets the position of crank  41  on shaft  9  (see  FIG. 3 ). Such adjustment is necessary to accommodate fish of different widths. Crank  41  can actually freely rotate on shaft  9 . Co-rotation of crank  41  with shaft  9  is effected by a fixed member  45  on the shaft which contacts the crank through adjustment screw  44 . As a result of this the guide plates always open to be parallel to the sides of the channel but without restricting the upward pivoting of gun assembly  3 .  
         [0059]     A chin plate  46  is shown in  FIG. 5 . Chin plate  46  is connected to a shaft  47  journalled to bearings not shown in the drawing in the side walls of the channel. A crank extends away from each end of the shaft, one of which cranks is item  48 . Crank  48  is pivotally connected to an end of link  27  (see  FIG. 3 ).  
         [0060]     On upward rotation of the gun assembly, it will be appreciated that chin plate  46  is rotated because of the action of link  27  on crank  48 . This causes the chin plate to lie essentially flat against the floor aiding passage of a fish beyond the set point after firing of the gun. As noted above, the slots in the links compensate for the different position of shaft  25  (see  FIG. 3 ) relative to chin plate  46  with adjustment of the position of gun assembly  3 .  
         [0061]     With reference to  FIG. 6 , there is shown portion  49  of trigger assembly  18  included in  FIG. 2 . In portion  49 , contact plate  19  and arm  20  can be seen. A normally open valve  50  and normally closed valve  51  are mounted to arm  20 . The rollers  52  and  53  of valves  50  and  51 , respectively, are acted on by a ramp  54  which extends from contact plate  19 . The trigger is in fact shown in the “fired” configuration. That is, contact plate  19  has been pivoted towards the rest of the assembly such that ramp  54  engages rollers  52  and  53  thus actuating valves  50  and  51 . Contact plate  19 —and hence also ramp  54 —is held in the fired position by an over-centre magnetic “spring”, the components of which are items  55  and  56 . This spring conversely holds the trigger in a cocked position when the device is reset to a “ready to fire status” (see below). Since spring  55 / 56  holds contact plate  19  in a fired position once firing has occurred, multiple firing is not possible. The trigger is thus a “dead trigger” which has to be reset.  
         [0062]     Ramp  54  can be seen to be bilateral. The portion  57  of the ramp that contacts roller  52  of valve  50  is steeper than the portion  58  that contacts roller  53  of valve  51 . Consequently, valve  50  is activated before valve  51 . Conversely, there is delayed activation of valve  51 , albeit by milliseconds. The function of the delayed actuation of valve  51  will be explained below.  
         [0063]      FIG. 7  shows the exit sensor  4  of device  1  of  FIG. 1 . This comprises a flap  59  on a shaft  60  the ends of which are journalled into bearings on the side walls of channel  2  of device  1  (see  FIG. 1 ). An arm  61  extends inwardly of shaft  60  and is positioned so that its end can contact the roller of roller lever valve with idle return  62 . Valve  62  is orientated so that actuation only occurs (momentarily) on return of flap  59  to its normal position after the fish has completely exited the device. That is, the valve is not actuated when arm  61  contacts the valve during the rotation caused by the fish passing under the exit sensor and is only momentarily actuated on return of flap  59  to its rest position.  
         [0064]     To allow for variable resetting of the device after firing of gun assembly  3 , the angle between arm  61  and flap  59  is adjustable. The lower portion  63  of flap  59  can comprise a removable section to adjust the sensor for fish of different heights.  
         [0065]     The entry control module  5  referred to above in connection with  FIG. 1  is shown in detail in  FIG. 8 . The module comprises a first flap  64  and a second flap  65 , both of which are pivotally mounted across the top of the channel  66  which comprises the module. Both flaps can be independently pivoted and are biased towards rest positions in which the flaps are vertical.  
         [0066]     Flap  64  has associated therewith a cam clutch  67  which incorporates a disk  68 . There is a caliper  69  included in the module which when activated acts on the disk to brake the cam clutch. When braked, cam clutch  67  prevents pivoting of flap  64  inwardly although it can still return to its rest position. A pneumatic cylinder under constant pressure can optionally be linked to gate  64  to aid return of the gate to its rest position.  
         [0067]     Braking is controlled by a mechanism depicted in  FIG. 9 . In this figure, cam clutch  67  of  FIG. 8  has been omitted for clarity. A rod  70  extends from a pivotal connection on a crank  71  on flap  65  through a supporting sleeve  72 . Supporting sleeve  72  is fixed at the end distal flap  65  to a plate  73  which carries a normally closed roller valve  74 . Plate  73  is pivotally connected to a crank  75  on flap  64 . The free end  76  of rod  70  is beveled and with both flaps  64  and  65  in their rest (vertical) positions is near roller  77  of valve  74  but not in contact therewith. However, extension of rod  70  causes beveled end  76  to contact roller  77  thereby actuating valve  74 . Actuation of valve  74  can only occur when flap  65  has been rotated inwards to a-greater degree than flap  64 .  
         [0068]     Flap  57  of exit sensor  4  and flaps  64  and  65  of entry control module  4  typically comprise a sheet of stainless steel. Rather than comprising a sheet, any one of these flaps can comprise a plurality of cross-pieces or a panel of mesh material or a grille fixed between a frame. Such a flap is not affected by a flow of water through the device.  
         [0069]     The device components described above are controlled and operated pneumatically. Device  1  thus includes a regulator for supplying air to the various components of the device at a suitable pressure (typically 400 to 700 kPa).  
         [0070]     The channel of the device is typically covered when in use to prevent operator injury through contacting the moving parts of the device. The cover is advantageously pivotally mounted to the channel and includes a safety lock which shuts off air supply to the device but fires gun assembly  3  when the cover is lifted.  
         [0071]     The pneumatic control circuitry of the device is depicted in  FIG. 10 . The circuitry comprises an air supply  78  which supplies air to impact cylinder  8 , valves  50  and  51  of trigger assembly  18 , valve  62  of exit sensor  4 , valve  74  of entry control module  5 , and five-way memory valve  79 . These components are supplied by lines  80  to  84 , respectively. Actuation of valves  50  and  51  through movement of contact plate  19  of trigger  18  closes of air flow to impact cylinder  8  but allows air to flow to memory valve  79  via lines  85  and  86 , respectively. The stoppage of air to impact cylinder  8  fires the gun while the supply of air to memory valve  79  sets the valve so that air can flow via line  87  to the end  88  of ram  12  to effect pivoting of gun assembly  3  ( FIG. 1 ) to the raised position. Air can also flow to OR valve  89  via line  90  to actuate brake cylinder  91  via line  92  which operates brake caliper  69  of the entry sensor module  5  (see  FIG. 10 ). Air can also flow to OR valve  89  via line  93  when valve  74  is open.  
         [0072]     On exiting of a fish, valve  62  is actuated causing a pulse of air to be directed via line  94  to the side of memory valve  79  opposite the side to which air is supplied by line  86 . This causes a resetting of the memory valve so that air is directed to end  95  of ram  12  via line  96 . This results in a reversal of ram  12  action which pivoted gun assembly  3  into the raised position so that the assembly returns to the lowered (firing) position. The actuation of valve  62  also allows a pulse of air to flow via line  97  to single acting pneumatic ram  98  which resets contact plate  19  of trigger assembly  18  (see  FIGS. 2 and 6 ). When contact plate  19  is reset, valve  50  causes air to flow to impact cylinder  8  which causes striker  21  to retract into sleeve  8  and the gun to be recharged.  
         [0073]     It will be appreciated from the above by a person skilled in the art that OR valve  89  allows supply of air to the brake cylinder via two paths. Consequently, closure of valve  74  alone will not allow release of the brake. Such release can only occur when exiting of the stunned fish has been detected by exit sensor  4 . This detection results in shut-off of the air supply to the OR valve via line  90 .  
         [0074]     A variant of the exit sensor  4  (see  FIG. 1 ) is depicted in  FIGS. 11 and 12 . In the former figure, valve  62  can be seen as well as an arm  99  extending from shaft  60 . Arm  99  has at its distal end a plate  100  which gives a longer signal on contacting roller  101  of valve  62 . Valve  62  is rotated relative to its position in  FIG. 7  to allow the correct geometry with regard to contact plate  100 .  
         [0075]     To give more positive control over the return of flap  59  (see  FIG. 7 ) of exit sensor  4  to its rest position, a pneumatic cylinder under constant pressure (to act as a spring) and a one-way damper can be linked to the flap. These items are shown (in part) as items  102  and  103 , respectively, of  FIG. 12 . Cylinder  102  has a rod  104  (which is connected to a piston within the cylinder) extending therefrom linked to shaft  60  of flap  59 . On opening of gate  59 , rod  102  is forced into cylinder  102 , the pressure therein forcing the rod in the opposite direction to rotate flap  59  to the vertical rest position. It will be appreciated that the force exerted by cylinder  102  is at a maximum when the flap is in the vertical rest position and at a minimum when the flap is fully open. This is the opposite of the force of gravity on the flap.  
         [0076]     The one-way damper  103  of  FIG. 12  is linked to shaft  60  by crank  105 . On opening of gate  59 , rod  106  (which is connected to a piston within the damper) is drawn out of the damper. On return of the flap to its vertical rest position, further rotation beyond that position is resisted by the damper. The presence of the damper also prevents oscillation of the gate about the vertical rest position on return thereto. In addition to flap  59 , a portion of side wall  107  of device  1  ( FIG. 1 ) can be seen in  FIG. 12 .  
         [0077]     The operation of the device is described in the following paragraphs. 
        a) Prior to admission of a fish, gun assembly  3  is in the lowered (firing) position and trigger assembly  18  is armed. That is, contact plate  19  is pivoted away from valves  50  and  51  so that ramp  54  is not in contact with the rollers of the valves. Flap  59  of exit sensor  5  is in the rest position as are flaps  64  and  65  of entry control module  5 . The guide plates (see, for example, item  37  of  FIG. 4 ) and chin plate  46  are in the inward and raised positions, respectively.     b) On entering the device, a fish advances to the set point which is where the nose of the fish meets contact plate  19  of trigger assembly  18 . Pivoting of the contact plate actuates valves  50  and  51  which results in: 
            i) firing of impact cylinder  8  so that striker  21  stuns the fish;     ii) resetting of memory valve  79  with actuation of ram  12  and hence pivoting of gun assembly  3 ; and     iii) coincidentally with the pivoting of gun assembly  3 , pivoting of the guide plates to their open positions (essentially parallel with the channel walls) and the lowering of the chin plate).    
            c) A fish at the set point is detected by entry control module  5  which locks flap  64  and prevents entry of a further fish.     d) Passage of the stunned fish past the set point (possible because of the pivoting of gun assembly  3  to the raised position, and the coincidental pivoting of the guide and chin plates) and out of the device is detected by exit sensor  4  which results in: 
            i) resetting of memory valve  79  with actuation of ram  12  and hence pivoting of gun assembly  3  to the lowered (firing) position;     ii) coincidentally with the pivoting of gun assembly  3 , pivoting of the guide plates to their inward positions and the raising of the chin plate;     iii) actuation of ram  98  and hence rearming of trigger assembly  18 ;     iv) recharging of impact cylinder  8 ; and     v) shut-off of air to brake cylinder  92  which releases the brake on flap  64  so that another fish can enter the device.    
               
 
         [0090]     It will be appreciated that steps (a) to (d) represent a complete cycle which is repeated for the stunning of further fish.  
         [0091]     The foregoing embodiments are illustrative only of the principles of the invention, and various modifications and changes will readily occur to those skilled in the art. The invention is capable of being practiced and carried out in various ways and in other embodiments. It is also to be understood that the terminology employed herein is for the purpose of description and should not be regarded as limiting.  
         [0092]     The term “comprise” and variants of the term such as “comprises” or “comprising” are used herein to denote the inclusion of a stated integer or stated integers but not to exclude any other integer or any other integers, unless in the context or usage an exclusive interpretation of the term is required.  
         [0093]     Any reference to publications cited in this specification is not an admission that the disclosures constitute common general knowledge in Australia.