it is well known to biologists that fish have two groups of muscles . a first group , known as red muscles , are disposed along opposed sides of the body of the fish . these muscles are the swimming muscles . they are alternatively contracted to effect undulation and swimming motion by the fish . these muscles are relatively small sized but have great stamina and can be continuously active for long periods of time . the remaining muscles in a fish are referred to as white muscles . these muscles perform all the remaining body functions . they are generally large sized , very powerful and rapidly responding to a triggering impulse . generally , they are pairs of muscles located on opposed sides of a fish . when paired groups of muscles are triggered , a contracting reaction occurs . normally , cessation of the triggering impulse whether internally or externally induced , permits relaxation of the muscles . when the paired groups of muscles are overwhelmed by triggering impulses which preclude alternating relaxation , epileptic seizure occurs . because of the substantial power of the white muscle groups , severe damage to the fish occurs during such seizure . the power of the muscles is sufficient to break or dislodge the spinal column ; this injury is often fatal . a tearing of secondary muscles and tissues occurs which produce massive hematomas which are often fatal . epileptic seizure of the white muscles can cause both short term and long term damage or injury to organs and may result in immediate or delayed death . many of these injuries are not immediately visually apparent . usually , x - ray films must be analyzed or autopsies must be performed to learn the extent of the injuries . for years it has been thought that the red muscle tissues , which are responsible for the sustained swimming motion , were overwhelmed by electrical impulses due to a high field strength proximate an electrode during electrofishing . that is , it was believed that the degree of injury to fish was a function of the power level used during electrofishing and that the damage and injury was due to contractions of the red muscle groups . based upon information supplied by biologists , it is generally accepted that the red muscle tissues are insufficiently powerful to break the spinal column or cause massive organ and tissue damage which has been found in fish injured by electrofishing . the white muscle tissues are , however , sufficiently powerful to cause the fatal or near fatal injuries . one must therefore conclude that the white muscle tissues are responsible for a significant part of the injuries caused during electrofishing . since field strength , for any given power input , is to some extent a function of the anode size , it was believed that modification of the electrode configuration would have a salutary effect in reducing the injury rate from approximately 50 % to a very acceptable rate of less than 10 %. experiments indicate that a reduction in field strength due to a particular electrode configuration had little effect upon reducing the injury rate . the main difference appears to be that the distance at which electrotaxis resulted was substantially reduced . as fish transition from electrotaxis to narcosis , the muscles relax and the fish essentially stop swimming . depending upon the direction of the water current and other factors , migration of the fish toward the anode electrode may occur . such migration will subject the fish to more intense or higher power level field strength . tetanus may result with attendant severe or fatal injuries . to prevent injury to fish during electrofishing , apparatus must be developed which affects the red muscle tissues to induce electrotaxis without simultaneously or subsequently causing contraction of the white muscle tissues . based upon substantial experimentation and testing , a pulse train has been developed which includes high frequency pulses for stimulating the red muscle tissues and a sufficiently low repetition rate to permit the white muscle tissues to relax between contractions and thereby prevent epileptic seizure . a circuit for developing such a pulse train is illustrated in fig1 . operation of this circuit has been effective at various power levels tested . at different power levels , only the distance at which electrotaxis is first induced varies ; the injury rate does not seem to be a function of the power level . moreover , different electrode configurations to modify the maximum field strength to which the fish may be subjected has had no significant effect upon the injury rate and has only affected the distance at which electrotaxis first occurs . the pulse train transmitted by the circuit illustrated in fig1 includes a plurality of packets , each packet having a plurality of high frequency pulses , which packets are repeated at a low frequency rate . the high frequency pulses will stimulate the red muscle tissues . the low repetition rate permits any contracted white muscle tissues to relax between contractions . with such relaxation , the white muscle tissues will not suffer epileptic seizure . without epileptic seizure , significant damage to the fish will not occur . referring to fig1 there is shown a circuit 10 for generating a plurality of packets of high frequency pulses repeated at a low frequency rate to produce a high voltage direct current for use in electrofishing . the circuit includes three sections . a power supply , designated by block 12 , provides plus and minus 12 volts dc to the various circuit components . a high voltage dc section , designated by block 14 , provides the output signal to a load r l representative of the anode electrode used in electrofishing . a timing / scr drive section , designated by block 16 , controls the shape and frequency of the pulse train present at the electrode anode ( r l ). power supply 12 may be a conventional power supply wherein the primary coil 18 of transformer 20 is connected across an alternating current power supply 22 . secondary coil 24 provides power to a bridge rectifier br2 . the dc output of the bridge rectifier is smoothed by capacitor c 4 and regulated by voltage regulator vr 1 . a + 12 volt dc output is provided between conductor 26 and ground 28 . a second bridge rectifier br3 is connected across secondary coil 30 of transformer 20 to provide a dc output . the dc output is smoothed by capacitor c5 and regulated by voltage regulator vr2 . a - 12 volt dc voltage is provided between conductor 32 and ground 28 . referring to high voltage dc section 14 , a full wave bridge rectifier br1 is connected across power supply 22 to provide a high voltage direct current between conductor 40 and ground 28 and across series capacitors c1 , c2 . when silicon controlled rectifier scr1 is turned on , power is applied across the load r l . silicon controlled rectifier scr2 turns off scr1 via commutating capacitor c 3 . the voltage level at the anode electrode ( r l ) is adjusted by a phase control circuit . that is , potentiometer p 1 is adjusted to fire diac d 1 at a selected point of the 60 cycle alternating current input . when diac d 1 fires , triac tr 1 is turned on . choke l 1 provides di / dt protection for triac tr 1 . the timing cycle produced by timing / scr drive section 16 begins with low frequency oscillator u 1 . the frequency of this oscillator controls the repetition rate of the high frequency burst ( packet of pulses ). a high output at pin 3 of u1 is transmitted to pin 6 of flip flop u2 via conductor 45 . the wave form of this pulse is illustrated in fig2 a . the output of flip flop u2 at pin 1 is an extended pulse , as represented in fig2 b . it enables , via conductor 46 , high frequency oscillator u3 . an output at pin 2 of flip flop u2 enables counter u5 via conductor 48 . the frequency of oscillators u1 and u3 can be adjusted by potentiometer p 1 connected to pin 7 of oscillator u1 and by potentiometer p 3 connected to pin 7 of oscillator u3 . the output of oscillator u3 on pin 3 is transmitted along conductor 50 to the trigger input at pin 2 of a one shot multi vibrator u4 ; the pulse train is depicted in fig2 c . the output pulse width of one shot multi vibrator u4 is controlled by potentiometer p 4 connected to pins 6 and 7 . as shown in fig2 d , the pulse width of the pulse train at pin 3 of one shot multi vibrator u4 and conveyed on conductor 52 is , in example , approximately 2 . 9 milliseconds ( ms ). the repetition frequency of the pulses is approximately 4 . 17 ms ( 250 hz ), as is also indicated in fig2 c for the output of oscillator u3 . the output of one shot multi vibrator u4 is conveyed to pin 14 of counter u5 via conductors 54 , 56 . the leading edges of the pulses transmitted to the counter initiate the counting . in the example illustrated in fig2 a to 2h , the number of pulses per packet has been set at 3 . accordingly , the output of counter u5 occurs on conductor 58 at each third count , as illustrated in fig2 g . the output pulse from counter u5 is transmitted via conductor 58 to pin 4 of flip flop u2 . when pin 4 goes high , the flip flop is reset . the resetting disables the pulse train at output pin 1 and oscillator u3 is disabled . the commensurate output at pin 2 of flip flop u2 is transmitted via conductor 48 to pin 15 of counter u5 to reset / enable the counter . it may be noted that the number of pulses in each frequency burst is a function of the selected output pin of counter u5 to which conductor 58 is connected . the output of one shot multi vibrator u4 is buffered through transistors t1 , t2 and comparator u6 . the rising edge of the square wave present at collector 60 of transistor t2 is coupled to gate 62 of silicon controlled rectifier scr1 via capacitor c13 . the wave form at collector 64 of transistor t2 is depicted in fig2 e . transistor t3 inverts the wave form present at collector 60 . the resulting pulses at collector 64 of transistor t3 are depicted in fig2 f . the rising edge of each pulse at collector 64 is applied to gate 66 of silicon controlled rectifier scr2 via capacitor c14 and conductor 70 . when silicon controlled rectifier scr2 turns on , silicon controlled rectifier scr1 is turned off . similarly , when silicon controlled rectifier scr1 is turned on , silicon controlled rectifier scr2 is turned off . the resulting pulsed dc output across load r l is depicted in fig2 h . as noted , the individual pulses may be approximately 2 . 9 ms in width with a repetition frequency of 240 hz . the three pulses occur at the beginning of a 66 . 6 ms pulse train , which is equivalent to a low frequency of 15 packets per second ( 15 hz ). each pulse of the three pulse packet depicted in fig2 h is a relatively high frequency pulse sufficient to trigger contraction of the red muscles in a fish . the relative low frequency pulse train repetition rate of 15 hz has been well documented to be sufficiently low to permit relaxation of any contracted white muscles and epileptic seizure of such muscles is precluded . the number of pulses per packet is believed to be variable in the range of 2 to 5 pulses per packet without resulting in any substantial injury to most fish . the pulse width may be varied at least within the range of 5 to 25 packets per second . to summarize our understanding of the important features of our invention , the following conclusions are presented . spinal compression injury and other internal traumas are the result of over stimulation ( leading to an epileptic seizure ) of paired white muscle systems in the fish . low frequency pulses of dc current , e g ., 15 pps with a pulse width of 10 milliseconds , virtually eliminate the problem . however , low frequency does not stimulate good electrotaxis . using high frequency pulses of narrow width in packets at approximately 15 packets per second retains the low injury rate and causes good electrotaxis response . based upon experience to date , the shape , frequency , width and the ratio of the high and low components of the pulse train are all sensed by the physiological systems of the target fish more specially , the benefit of low injury and effective electrotaxis is dependent upon a ) low &# 34 ; packet of pulses &# 34 ; frequency ; b ) shape , width , and number of high frequency pulses in each packet ; and c ) the ratio of the packet frequency to the number of the high frequency pulses per packet . if the number of packets per second is reduced ( say from 20 to 10 ) then the number of high frequency pulses per packet needs to be increased ( say from 3 to 4 ) in order to have the best overall results . if the number of high frequency pulses per packet is too great , fish will be narcotized too far from the anode electrode for easy capture . if the number is too low , the catch efficiency will decrease . if the number of packets is too high , the incidence of injuries will increase ; if too low , the catch rate will be down . that is , there is an optimum ratio which our inventions allows the operator to choose to suit the type of fish and environment for a given electrofishing effort . while the principles of the invention have now been made clear in an illustrative embodiment , there will be immediately obvious to those skilled in the art many modifications of structure , arrangement , proportions , elements , materials and components used in the practice of the invention which are particularly adapted for specific environments and operating requirements without departing from those principles .
to minimize injury during electrofishing while inducing a high degree of electrotaxis , a packet of dc pulses having sharp leading edges and preferably an exponential or square decay are transmitted under water between an anode electrode and a cathode electrode several times each second to stimulate contraction of the red muscle tissues and bring about electrotaxis without inducing epileptic seizure of the white muscle tissues of fish and thereby avoiding injury to the fish .