Introduction to Electrofishing

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INTRODUCTION TO ELECTROFISHINGELECTROFISHIIUG PRIITICTPTESLOW CONDUCTIVITY WATERDistilled water is a very good insulator. It has aconductivity range of 0.5 to 5.0 microSiemens/A fish will receive the maximum shock through its body whencc. If a normal voltage is applied in distilledthe conductivity of the water is the same as the conductivity ofwater, very little cunent will flow. Power flow isthe fish's flesh. Unfortunately, this is rarely the case.too low to be effective for electrofishing.Fish flesh conductivity ranges from 500 to 1,500 microSiemens/The current passing through a fish decreasescc. Each species has a different conductivity. This affects theiras the power flow decreases. To get the samesusceptibility to electric cunent.response from fish, the cunent can be maintainedConductivities for some fish species are:by either increasing the voltage, or by keepingTrout I,220 microSiemens/ccthe resistance low.Perch I,089 microSiemens/ccIf a higher voltage is used, up to 1,200 volts mayCarp 870 microSiemens/ccbe necessary. High voltages create three problems,Grudgeon 814 microSiemens/ccspecial electrical equipment is required, safetyE. Halsband - Vilbert 1967is reduced for the operators, and conditions are FISH SIZElethal for fish close to electrodes.Among fishTheof the sameresistancespecies,canthe largerbe keptfishlow by increasingare more sensitivetheto electrical currents. Fishsizeabsorb powerof the electrodes. Theasonly limitationsa functionto thisof bodysurface area. This isare the availabilityimportanto rememberof largerif youelectrodes,areand theshockingfor small fish and largeweightfish areof electrodealso present.thatThecan be handledlargebyfishthearegoing to receive a much greateroperator.shock than the small fish.HIGH CONDUCTIVITY WATERFISH CONDUCTIVITYTEMPERATUREWater conductivityHighandconductivityeffective fishisconductivityover 2,000 microSiemens/increase withhigher temperature.cc. If a high voltage is applied, most cunent willConductivities reportedflowforeasily throughCarp:the water and the fish will50 372hardlymicroSiemens/ccbe affected. The electric current follows10" 543the pathmicroSiemens/ccof least resistance and bypasses the15'7r4 microSiemens/ccfish completely. Therefore use low voltages and20'1,026highmicroSiemens/cccurrents. Currents as high as 60 amps are25" 1,969 microSiemens/cccommon, the limiting factor being the rating ofWhitney andthe power-supply.Pierce 1957Some brackish water and industrial waste water SUBSTRATEhave conductivities over 10,000 microSiemens/Certain bottom substrates will conduct electrical cunent. Thesecc. Here smaller power-supplies are unable to weaken the electric field in the water, making fish capture lessdeliver enough power to stun fish. Waters in thiseffective.range can only be electrofished effectively withthe larger model GPPs.ADJUSTING THE VOLTAGEThe Smith-Root 7.5 GPP outputs 62 amps By adjusting the output voltage, the effects of the water'sthrough 8 gauge stranded cables. This unit can conductivity on electrofishing can be reduced.stun large fish in the interface between fresh and The current flowing through the water is directly related to thesalt water. For example, Striped Bass can be voltage applied. The higher the voltage, the greater the cunentstunned for taking brood stock.will be.Theoretically high conductivity could be dealt When adjusting the output voltage the major consideration is thewith by using smaller electrodes, but this would power being used. This is especially true for battery poweredreduce the range and also create damaging current electrofishers. Power is equal to the voltage multiplied by thedensities near the awww. smith -root.com ,17
INTRODUCTION TO ELECTROFISHINGELECTROFISHIIUG PRIIUCIPLEScurrent. When figuring the power for an electrofisher, The switch gives several on-off pulses per second. Thethe fact that it is usually putting out pulsed DC must number of pulses per second (pulse frequency) and thebe taken into consideration. The instantaneous power on time (pulse width) have different effects on differentduring a pulse may be quite high, but if the electrofisherspeciesfish.is only producing pulses ata257o duty cycle, the averageIn a pulsed DC field a fish's body flexes with each pulse,power would be approxim ately 257o of the instantaneous and returns to normal between pulses. This flexing andpower.straightening accentuates the involuntary swimmingtowards the anode. called galvanotaxis.ALTERNATING CURRENT6 " 0z2'FAlternating Current (AC) is an electrical current in whichthe direction of current flow reverses a number of timesGalvanotaxis: In pulsed DC a fish's bodyper second.flexes with each pulse.In an AC field, the fish takes a position transverse tothe electrical field lines and attempts to face the anode Smith-Root Programmable Output Waveforms give youand cathode successively, in rhythm with the AC cycle. complete control over your electrofisher output. ThisWhen the field strength increases, tetany occurs, and the patented method of synthesizing waveforms makes itfish is stunned. Strong contractions of the body musclespossibleto produce virtually any waveform, so you canmake the fish feel rigid.select the one that is safest for the fish. POW allows youAt high voltages, the larger fish may be killed, the to create nanow pulses to achieve the same results asmuscular contractions being so severe that vertebrae are wide pulses. Narrower pulses put less power into thefractured and the brain damaged. HenceAC electroflshingwater.This has three benefits: you have less chance ofis only successful with small fish in low conductivitydamageto the fish, your battery or fuel lasts longer, andwater.you can work in very conductive water that overloadsconventional electrofi shers.DIRECT CURRENTstraight strarght straight ''"'RESPONSE OF FISH TO DC FIELDSDirect Cunent (DC) is the term given to electrical currentthat flows only in one direction. The current flows from An electric field in water can be considered to have threethe negativelectrode (cathode) to the positive electrodeseparateareas. The outer peripheral area is a weak field(anode).that the fish is indifferento. The next area, closer to theThe reaction offish to direct current is quite different from electrodes, has a stronger electrical field, but not enoughtheir reaction to alternating cunent. The first reaction of to stun the fish. In this area, the involuntary swimmingthe fish is to turn toward the anode and start to swim action will occur and the fish will swim towards thetoward it until it reaches an electrical field strong enough anode. The innermost area has the strongest electricalto stun it. Being stunned is called galvanonarcosis. The field, and the fish within it are immobilized.severe muscle contractions caused by AC do not occur,and the fish recover much faster. Mortality rate is much Zone of Indifferencelower with direct cunent.When electrofishing first starts fish are usually hiding upto three meters away, so high power is required to attractPULSED DIRECT CURRENTthem out of hiding. But as the fish nears the anode, highEven greater anode attraction is possible with pulse direct power can injure it.current. Pulsed direct current is made by intenuptingsteady DC with an electronically controlled switch.18 www.smith- root.com1Iflqtqrlq rlc1q qqqqolqt''1qo1rlrlqGlGlclFtFtFtGl14de4G1clC1r,1
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Introduction to Electrofishing

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