MORTALITY OF SALMON FINGERLINGS

EXPOSED TO PULSATING

DIRECT CURRENT

BY GERALD B. COLLINS, CHARLES D. VOLZ

AND PARKER S. TREFETHEN

FISHERY BULLETIN 92

UNITED STATES DEPARTMENT OF THE INTERIOR, Douglas McKay, Secretary

FISH AND WILDLIFE SERVICE, John L. Farley, Director

ABSTRACTInfluences of voltage gradient, current density, pulse frequency, and

duration of exposure on the mortality of salmon fingerlings exposed topulsating direct current were examined experimentally in relation to thelength of fish, water temperature, and pulse duration, using a current ofsquare-wave form.

The experiments indicated that mortality increased with an increasein voltage gradient, in current density, or in both. The effect of voltagegradient increased with the duration of exposure. The total voltage towhich the fish were subjected (fish length X voltage gradient) was theeffective factor in mortality, rather than the voltage gradient, and theeffect of total voltage on mortality was actually greater on shorter fishwhen the exposure was only 30 seconds. Pulse duration was not a lethalfactor, and there was no direct relation between mortality and the totalenergy applied per UnIt of time. Under the conditions of these experi­ments' mortality increased with the pulse frequency, and the effect ofpUlse frequency on mortality increased with the length of the fish andthe duration of exposure.

The mortality of the fingerlings exposed to pulsating d. c. increased withthe duration of exposure, and the effect of duration of exposure increasedwith the length of the fingerlings. Mortality increased with the watertemperature, and the effect of water temperature on mortality increasedwith the duration of exposure. The effect of water temperature onmortality was greater on fish of greater length.

,..;,

UNITED STATES DEPARTMENT OF THE INTERIOR, DOUlllas McKay, Secretary

FISH AND WILDLIFE SERVICE, John L. Farley, Director

MORTALITY OF SALMON FINGERLINGS

EXPOSED TO PULSATING

DIRECT CURRENTBy GERALD B. COLLINS, CHARLES D. VOLZ, and PARKER S. TREFETHEN

FISHERY BULLETIN 92

From Fishery Bulletin of the Fish and Wildlife Service

VOLUME 56

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON: 1954

For sale by the Superintendent of DQCuments, U. S. Government Printing OOice, Washington :lS, D. C.

Price 30 cents

II

CONTENTSPage

Historical background_ __________________________________________ 61Mat.erials and methods:

Met.hod_____________________________________________________ 62Apparat.us__________________________________________________ 62~Ieasurcrncnts______________________________________________ 63Procedllre__________________________________________________ 63Controls___________________________________________________ 64Experimental lirnit.at.ions_ ___ ______ _____ __ __ ___ __ __ __ 64Graphs and computations. ___________________________________ 66

Experirnents:Volt.agc gradient and current density__________________________ 66Pulse frequency_____________________________________________ 70Pulse duration_ __ __ __ ____ __ _ _ ________ 72Fish length and duration of exposurc__________________________ 78Tcrnpcrature________________________________________________ 78

])iscussion ~___________ 78Sunlrnary______________________________________________________ 80Literature cited - _- - - - - - - _- - - - - - - - - - - ___________ 81

MORTALITY OF SALMON FINGERLINGS EXPOSED TO PULSATINGDIRECT CURRENT

By GERALD B. COLLINS, CHARLES D. VOLZ, and PARKER S. TREFETHEN, Fishery Research Biologists

HISTORICAL BACKGROUND

Protectioil of salmon fingerlings on their down­stream migrations is one' of the major problemsto be solved if the salmon fishery of the PacificNortll\vest is to be maintained at its presentlevel. Water resources are being developed forpower, irrigation, navigation, and flood control ata ra.pidly accelerating pace, and the cumulativeeffect of many dams and water diversions seriouslythreatens this important natural food resource.

Mechanical' screening is used nt some of thesmaller installations to prevent fingerlings frombeing swept into turbine intal.:es or into water

. diversions, but it is expensive to install nnddifficult to maintain. At la.rger dams, wherehuge volumes of water are involved, mechanicalscreens a·re generally eonsidered impractical.

Electric screens have bee.1 in use for more than30 years, with most applications endeavoring toestablish an electrical field as a barrier or "fence"to prevent entrance of fish into a given area.These have generally been llnsatisfactory withmigrating fisb, and particularly so with dow./).­stream-migrating salmon. The fingerlings seemunable to avoid the electrical field and are stunnedor even killed rather than diverted.

Attention has been turned to the use of thedirectional properties of electric fields as a meansof diverting the downstream migrants fromhazardous areas. For many years it has beenknown that under certain conditions when fishnre subjected to dire.ct current (d. c.), the fishtend to move toward the positive electrode.Advances in the field of electronics now make itseem likely that this behavior can he put topractical use in controlling the movements ofsalmon fingerlings. Toward this end the UnitedStates Fish and Wildlife Service has initiateda program of research on electrical fish guidingwhich includes basic laboratory studies as wellas large-scale field experiments. The material

presented here is a report on one aspect of theresearch in progress.

A prerequisite to field experiments on electricalfish guiding is a knowledge of the electrical con­ditions that are injurious or lethal to fish. Therange of electrical conditions to which fish canbe subjected safely should be defined in advllJ1ceto avoid the possibility of destroying large numbersof migrating fish during field tests.

Although the effect of electric current uponfish has been a subject of interest and researchfor at least 50 years, relatively little attentionhas been paid to its effect upon the morta.Iity offishes. Scheminzky (1924) outlined the reactionsof fish subjected to electric current that occurat successively higher energy levels as follolvs:(1) The threshold of sensory recognition, (2)electrotaxis, (3) electronarcosis, and (4) at thehighest energy level, death. Most of the researchhas been concerned with the responses at thethree lower levels, and observatio.as on mortalityhave been largely incidental.

Experimenting with electric fish screens, McMil­lan (1928) described tests using alternating current(a. c.), in which the mortality of salmon fingerlingsincreased with increases in voltage gradient andcurrent density. He also pointed out the directrelation of mortality to the duration of exposure.Groody, Loukashldn, and Grant (1950), investi­gating electrotaxis of sardines, reported a relationbetween current density and mortality that de­pended upon the size of the fish and the durationof exposure, which relation they found to be "espe­cially true whea nonpulsating current was used."Similar observations by research workers studyingthe effects of electric fish screens and elect.ric fishshockers were usually based on reactions to con­tinuous d. c. or to a. c. In general, the observa­tions on mortality which were made during inves­tigations of recognition thresholds, electrota..~is, orelectronarcosis, were inadequate for the purposesof the present study on electrical guiding of salmon

61

62 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

fingerlings. A more detailed understanding of thefactors affecting the mortality of salmon fingerlingsexposed to pulsating or interrupted d. c. wasneeded. I.l the laboratory experiments describedin the following pages, the mortality of salmonfingerlings subjected to pulsating d. c. was meas­ured in relation to factors such as the voltagegradient, current density, pulse frequency (pulserepetition rate), pulse duration (pulse width),water temperature, size of fish, and duration ofexposure.

Charles Ellis, supervisor of hatcheries, State ofWashington, and Lewis Garlick, regional super­visor, Branch of. Game Fish and Hatcheries, Fishand Wildlife Service, made available the supplyof salmon fingerlings used in this study: Thecooperation of persollllel at the Green River, Issa­quah, and Samish hatcheries of the State of Wash­ington and the Leavenworth hatchery of the Fishand Wildlife Service is gratefully acknowledged.Fishery aids Robert H. Lander and Gene D. Chardof the Fish and Wildlife Service carried out manyof the tests and assisted in compiling the data andin preparing the material for publicn.tion. Pro­fessor Lorne Kersey, University of British Colum­bia, Professor George Hoard and Leon Verhoeven,University of Washington, and Harlan Holmesand Elizabeth Vaughan, Fish and Wildlife Service,critically reviewed the manuscript and offeredmany helpful suggestions.

MATERIALS AND METHODS

The experiments were conducted from May toAugust 1952, at the laboratory of the UnitedStates Fish and Wildlife Service in Seattle, Wash.Chinook fingerlings (0. tsha'WIJtscha) which wereused in all tests (the one exception is noted) weretransported in milk cans from the WashingtonState hatcheries at Green River, Issaquah, andSarnish, and from the Federal hatchery at Leaven­worth, Wash., and were placed in circular, woodenholding tanks 4 feet in diameter and 3 feet indepth. The maximum holding period at the lab­oratory before the fingerlings were used in theexperiments was 4 days.

METHOD

A direct experimental approach was used inwhich two or three of the factors whose influencewas to be examined were each varied while otherfactors were maintained relatively constant. The

influence of voltage gradient, current density, pulsefrequency, and duration of exposure upon themortality of salmO!l fingerlings exposed to pulsat­ing d. c. was examined directly in relation to thelength of the fish, water temperature, and pulseduration. Fingerlings were held in uniform aline­ment with reference to the direction of the electri­cal field and were subjected for a specified timeto a pulsating d. c. field with defined characteris­tics. The fingerlings were then held 1 hour afterexposure, and the number of mortalities wasrecorded.

Mortality was interpreted to include any fishthat had not completely recovered equilibriumwithin 1 hour after exposure to the electrical field.This arbitrary definition was based on explora­tory tests in which 96 percent of the fish that hadnot recovered equilibrium within 1 hour afterexposure died within the ne.~t 6 hours.

APPARATUS

The experiments were performed in a rec­tangular plastic tank (fig. 1) in which two flat,stainless-steel, screen electrodes were suspendedperpendicular to the long R.'l:is. The electrodesexactly fit the inside dimensions of the tank toensure a uniform electrical field. Vertical stalls,2 em. deep, 1.5 cm. wide, and 12 cm. long, made ofthin pinstic were placed between the electrodes,parallel to the long axis of the tank, to keep thefish in alinement parallel to the field. In thetests in Which fish were alined across the field,stalls made of plastic screening were used. Plasticscreening at the end of the stalls and a plasticcover on the top prevented the fingerlings fromjumping out when electric current \Vas applied.The sides of the tank were marked in centimeterunits for convenience in establishing the distancebetween the electrodes.

Throughout the experiments, a current ofsquare-wave form was used (fig. 2). The pulsat­ing, or interrupted, d. c. was supplied by a spe­cially constructed ;quare-wave generator (fig. 3)which was made up of seven units. Unit 1, thepulse-rate frequency generator, used a .gas triode(6D4) as a relaxation oscillator, producing a saw­tooth wave of variable frequency (2 to 15 pulses asecond.) The flyback of the saw-tooth was dif­ferentiated by an RC network, and the negativepull;les produced were amplified and inverted by apentode (6AC7) pulse amplifier, unit 2. The

Ji'IGUHI; l.-Expcrilllcnl,al lank, 60 cnl. x 15 CIIl. x :I 1 CIIl.

FIG HE 2.-PhoLograph of WIW forlll on oscjllo~copc.

MORTALITY OF SALMON IN PULSATING CURRENT 63

(I)0. C. ,# D. C. POW ER

YOLTAGE /-/"~_-1 SUPPLY

CONTROL UNIT

J1f1fL

f5)

POWER

AMPLIFIERDRIYER

"'--'14""'t,-'" .J1J1JL121 ..t-.l\..I\. r---=CJ)=----" 1I1fU"PULSE MONOSTAlLE

1---+---1 AMPLIFIER- I--~--I 1---'--1GENERATOR INYERTER MULTIYI8RATOR

t __ .- J... J_ _ l_"""_Jt1.An R_ s.!!!'p.!-y_JI ONLYI

l;t I l;r ~

"'---':(1'""1-.., ..LI&:1..R R.E

FREQUENCYCONTROL

171POWERSUPPLY

UNIT

OURATIONCONTROL

GATE-LEYELCONTROL

LOADEUCTRODEI

INTROUIIH)

FIGURE a.-Block diagram of square-wave generator.

positive pulses from unit 2 trigge.red unit 3, twodual t.riodes (6SN7) as a monost~ble multivi­brator with It variable pE'riod of 5 to 300 milli­seconds, which controlled the duration of thepulse. The negative square wave from unit 3controlled the power pentode (6L6) driver stage,which inverted the pulse to produce a positivesquare wave to drive the power amplifier (unit 5),two dual triodes (6AS7G). The gate-level con­trol on stage 4 controlled the cutoff bias of thepower-amplifier stage and was used as a zero-setand fine-voltage control for the output. Theplate supply for the power amplifier containedtwo mercury-vapor rectifiers (872-A). The pri­mary voIt.age of the plate transformer was con­trolled .to provide output-voIt.age control, variablefrom 0 to 600 voIt.s, at a maximum drain of 1.25amperes. The square-wave output of unit 5 wastaken across It resistor in the cathode returns ofthe 6AS7G tubes. Plate, bias, and heater volt­ages were supplied by a separate power unit (7),which had power·.rectifier (5V4G), bias-rect.ifier(6X4), and voltage-regulator tubes (2-QD3,l-QB3, and 1-0A2), plus the necessary trans­formers, chokes, capacitors, and resistoI'8.

MEASUREMENTS

Voltage was measured with a calibrated cathode­ray oscilloscope. Voltage gradient was calculatedfrom the distance between electrodes and the totalvoltage across the electrodes, since measurementsmade with the plastic stalls and screens in placeshowed the field to be uniform within the limits ofthe measuring equipment.'

The specific resistance of the water was meas­ured by a conductivity bridge. Current densitywas computed from the resistance of the waterand the voltage gradient. Current-densit.y com­putations were checked against measurementsmade by reading voltage across a precision re­sistor (1 pereent).

Pulse frequeney was calibrated by a low-fre­quency oscillator and checked frequently bymeans of a stop watch at low rates, and by visualoscilloseope comparison with 60-cycle sine wavesat rates of from 5 to 16 pulses a second. Fre­quency stability was within 1 percent.

Pulse duration was calibrated against a low­frequency oscillator by use of a direct-coupledelectronic switch. The accuracy and stabilitywas 1.0 millisecond.

Fish lengths are total lengths from. tips ofsnouts to extreme ends of tails.

All measurements of electrical characteristicswere accurate to within 10 percent and most t.owithin 5 percent.

PROCEDURE

Fingerlings, in groups of 10, were placed in thestalls in the area between the electrodes in the

64 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

plastic tank. No attempt was made to head thefish toward either electrode after exploratorye.~periments failed to reveal any significant. dif­ference in mortality between fingerlings headedtoward the positive electrode and fingerlings fac­ing away from it. A cover was placed over thetop to prevent the fish from jumping out, then theelectric current was turned on, and the duration ofe~posure was timed by a stop watch. Immedi­ately after exposure the fingerlings were placed inaerated glass bowls where they were held for 1hour. At the end of that time the dead fish andthose that had not completely recovered equi­librium were removed, and their number andlengths recorded. The number and lengths ofthe remaining fish ,vere also recorded.

During most of the tests, to minimize the needfor adjustment to new water conditions, the waterused in the experimental tank and in the aeratedbowls for holding the fish after exposure wastaken from the large holding tank when the fishwere brought into the laboratory. The temper­ature and resistance of t,he water were usuallymeasured every fourth exposure; hO\vever, duringtests examining the effect of current density, theresistance of the water was measured before eachexposure and the ,vater was adjusted to the de­sired resistance by the addition of dist.illed wateror an NaCI solution.

During tests examining the influence of watertemperature, fingerlings were placed in largeaerated containers, and temperatures were gradu­ally raised or lowered at a rate of change less than2° C. per hour until the desired temperature wasreached. The fish were exposed to the electricalfield at the desired temperature and were heldfor 1 hour after exposure at the same temperature.

Throughout these experiments fingerlings weree.~posed to an electrical field only once (a fishsurviving one test was never used in another) toavoid any possible effect due to conditioning.

CONTROLS

To ensure that mortality was not the resl~lt ofhandling, confinement, temperature change, etcetera, with each new supply of fishes, a controlgroup was subject,ed to the same treatment a.s theexperimental fish with the exception that powerwas not turned on. Among 3,800 fingerlings usedas controls the mortality was only 0.5 percent.

EXPERIMENTAL LIMITATIONS

Lack of control over witter temperatures inholding tanks and wat,er sources for experiments(except in the circumstances described in Pro­cedure) resulted in experiments being cltrried outunder a rather wide range of temperatures. Theexperiments began in May and continued untilAugust with water temperatures increasing from10° to 19° C.

The procedure followed in the experimentstended to minimize the effect of variation oftemperature upon the slope of the curves shown.Fingerlings in groups of 10 were subjected to acomplete range of the variables being examinedeach time the tests were run. The entire experi­ment was then repeated several times at a laterdate until the numbers of fish were sufficientlylarge. Thus one part of the curve ,vas notdetermined at one temperature and another partat a different temperature. The curves representthe effect at the median temperature of the rangesho,vn.

The experiments began with fingerlings in the·sma.Iler size ranges, and a.s the season progressedthe sizes inc.reased. Usually only a limited rangeof le.ngth was available at one time. The fishwere taken from four different hatcheries through­out a period of 4 months. They were transportedand held under a v8.riety of conditions, andundoubtedly som~ groups were in better physicalcondition than others. An attempt was made toe~pose the fish from each group to the entirerange of all the variables being examined. Forthe experiments ill which large numbers of fishwere used, the data ineIude the reactions of severalgroups of fish, and the curve represents the effecton fish of the average physical condition.

Fluctuations in ,vater temperature and thephysical condition of the fish are probably re­sponsible for some of the scatter shown in the data.However, the validity of relations shown by thecompiled data was verified by e.~amining thesame relations in single tests with one group offish under a single set of conditions. Examplesof this method of verificlttion are shown by thecircled data in figure 12 and the insert in figure 14.

Another factor that must be considered is thedistortion of the lines of current flow due to thedifference between the resistance of the fish andresistance of the wnter. The voltage gradientsand current densities shown in the graphs are

MORTALITY OF SALMON IN PULSATING CURRENT 65

those existing in the water before the fish wereplaced in it and are not the voltage grndients andcurrent densities created within the fish. Meas­urements nmde during those experiments in

which there would be a ma.''l:imum distortion ofthe field (minimum electrode spacing, large fish,and water of high resistance) indicated that themaximum error due to distortion of the field

16

.76

•

14

.67

CURRENT DENSITY(MILLIAMPS I CM,2)

.29 .38 .48 .57

6 8 10 12

VOLTAGE GRADlE NT(VOLTS I C M.)

42

0 10 .19

80FISH

LENGTH

70~-5 CM..-7 II

.-9 II

.-11 II

60-I-ZW<..)

500::W0....->-I- 40..J<t •I-0::0~ 30

•

20•

10

FIGURE 4.-Combined effects of voltage gradient and current density in relation to fish length upon mortality of salmonfingerlings (Oncorhynchus tshau'ytscha) exposed to pulsating d. c. Tests run at 2 pulses/sec., pulse duration 20 milli­secs., temperature range 10.00 to 19.90 C., duration of exposure 30 seconds. Sizes of symbols correspond to fish num­ber categories: 10-49, 50-99, 100-199, and 200-227.

66 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

was less than 10 percent. For e."tample, measure­ments of the total current across the electrodesmade with no fish in the apparatus, with onefish in each stall, and with two fish in each stall,with electrode spacings varying from 20 cm. to50 cm. at a gradient of 1 volt/cm., and a waterresistance of 16,000 ohms/cm.s, were all in agree­ment within 10 percent. It is probable that someof the scatter in the data may be due to thedistortion of the electrical field, or perhaps toelectrolysis; however, it is unlikely that theerrors are great enough to seriously affect therelations shown.

GRAPHS AND COMPUTATIONS

The curves shown in figures 4 to 14 werecalculated by the method of least squares weightedto the number of fish at each point and includeall data with mortality values greater than zeroand less than 80 percent. Some of the relationsshown would probably be best described by sig­moid curves if the data were more complete,but for simplification straight lines of regressionhave been used to describe them.

The fish lengths indicated in the graphs are themidvalues of 2 cm. groupings (e. g., 5 cm. includeslengths from 4 cm. to 5.9 cm.).

EXPERIMENTS

VOLTAGE GRADIENT AND CURRENT DENSITY

To examine the combined effects of voltagegradient and current density in relation to fishlength upon the mortality of salmon fingerlingsexposed to pulsating d. c., a series of experiments

was run in which chinook fingerlings of differentsizes were subjected to a pulsating field at variouslevels of voltage gradient and current density.During each of these experiments, water tempera­ture, water resistance, pulse frequency, pulseduration, and duration of exposure were main­tained constant. The results of the tests aresummarized in figure 4, and the numerical dataare given in table 1.

The data indicate that above a certain thresh­old, mortality increases in proportion to eachincrease in voltage gradient and current density.There is no indication of a relation between thelength of the fingerlings and the combined effectof voltage gradient and current density llPonmortality.

The situation in the experiments described abovewas comparable to what would exist in field ap­plications of d. c. for guiding fish, in that theresistance of the water remained constant whilethe current density changed as the voltage gradientwas varied. To complete the study, it was decidedto examine independently the effect of currentdensity upon mortality of fingerlings exposed topulsating d. c. A series of experiments was runin which fingerlings of different - lengths wereexposed at various levels of current density whilethe voltage gradient was held constant. Thiswas achieved by modifying the resistance of thewater with NaCI solution. Water temperatures,pulse frequency, pulse duration, and duration ofexposure were also held constant during each ojthese e."tperiml'nts. The tests are summarizedin figure 5 and the numerical data. are shown intable 2.

TABLE I.-Combined effects of fJoltage gradient and current density in relat-ion to fish length on mortality of salmon fingerlings

Fish length of-

4 to 5.9 em. 6 to 7.9 em. 8 to 9.9 em. 10 to 11.9 em.

Numher Number Mortality Number Number Mortality Number Number Mortality Number Number Mortantyexposed dead (percent) exposed dead (percent) exposed dead (percent) exposed dead (percent)

---------1------------------------------------3 volts/em__• •• _3.5 volt./ern • _4 volts/em • ._4.6 volts/em. _5 volts/em _6.5 volts/em _6 volts/em _6.5 volts/em__ • .• __7 volts/em _7.5 volts/em__ • _10 volts/em .• _12.5 volts/em _15 volts/em __ • • _

2412

22713712379

20089

10088

16791

lOt

oo1132

14111714313859

o0. 4 ------24i- --------3- ------i~2- ------i02· -----·--6- ------5~9- ----·-i25- ---.-.-"6" -------4~8.7 69 1 1.4 • • •• • • _

2.4 _. •• • •• __ ._. ._. • _2. 5 _. • • • ••_. • •• • _

7.0 130 10 7.7 23 4 17.4 25 3 12.012. 4 • • • _17.0 • •15.9 12 2 16.7 • .• _

It.: I t~ i: ~: ~ I ~g I 18 I ~n I fg I 3~ I f~::56.8 135 105 I 77.8 I 24 15 I 62.5 14 I 8 57.0

MORTALI'ry OF SALMON IN PULSATING CURRENT 67

80 ~

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·it

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FISHLENGTH5 CM7 II

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10

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(MILLIAMPS / CM!)

FIGURE 5.-Effect of current density in relation to fish length and water temperat.ure upon mortality of salmon fingerlings(Oncorhynchus tshawytscha) exposed to pulsating d. c. Tests run at 4 volts/cm., 2 pulses/sec., pulse duration 20 milli­secs., duration of exposure 30 seconds. Sizes of symbols correspond to fish number categories: 2S-74, 75-149, and150-443.

TABLE 2.-EjJect of current density in relation to fish length a..nd water temperature on mortality of salmon fingcrU?&gs

Fish length oC-

Current density Tempera· 4 to 5.9 em. 6 to 7.9 em. 8 to 9.9 em. 10 to 11.9 em.ture

(0 C.) Number Number Mortality Number Number Mortality Number Number Mortality Number Num.ber Mortalitrexposed dead (percent) exposed dead (percent) exposed dead (percent) exposed dead (percent

---------------------------------0.17 milliamps/em '_ 10.0-19.9 157 I 0.6 -------66- --------0- ------ii--- 11 0 0

~--------- ---------- -------- .....0.21 milliamps/em '_ 20.0-25.0 17 0 0 10 0 0 ------iiiii- --------6- -------6:"ii0.22 milliamps/em '. 10.0-19.9 53 0 0 89 2 2.2 81 6 7.30.27 milliaml>S/cm '_ 20.0-25.0 15 0 0 58 0 0 28 6 17.9 14 0 00.31 milliamps/em '_ 20.0-25.0 39 1 2.6 44 0 0 -------77" -----·--ii- --'---ii~9- -------iii- --------2- ------i5~40.33 milliamps/em '_ 10.0-19.9 68 0 0 III 2 1.80.41 milliamps/em '_ 20.0-25.0 96 5 5.2 297 34 11.5 50 9 18.0 11 0 00. 53 milliamps/em '_ 10.0-19.9 ------25- -------i- ------4~ii-

89 \} 10.1 34 3 8.8 -------48- -··_·---6- ------i2~60.61 milliamps/em '_ 20.0-25. 0 156 13 8.3 54 15 27.80.72 milliamps/em '_ 10.0-19.9 23 3 13.0 83 4 4.8 81 6 7.4 28 0 00.78 milliampS/em '_ 20.0-25.0 41 11 26.8 108 33 31.5 45 20 44.4 10 1 10.01.\3 milli:lmps/em '_ 10.0-19.9 19 11 57.8 I\\l 10 14.5 120 5 4.2 34 2 5.111.21 milliamps/em '_ 20.0-25.0 30 11 ;16. 7 84 3. 44.0 34 20 58.8 26 4 15.41.93 milliamps/em '_ 10.0-19.9 20 15 75.0 20 9 45.0 ---------- ---------.

-----63~2-12 1 8.3

1.93 milliamps/em '_ 20.0-25.0 27 18 66.7 59 29 49.2 19 12 ---------- ---------- ----------

294325-54-2

68 FISHERY BULLETIN QF THE FISH AND WILDLIFE SERVICE

The data, although there is considerable scatter,particularly where only small numbers of fish areused, show a pattern similar to that in the experi­ments in which both current density and voltagegradient were varied. Above a certain thresholdmortality increased in proportion to the increasein current density, and there was no discerniblerelation between fish length and the effect of cur­rent density under the conditions of the experi­ments. The range of water temperatures in whichthe e.~periments were run was so great that thedata were divided into two groups to reveal theinfluence of water temperature upon the mortalityof fingerlings exposed to pulsating d. c.

The effect of voltage gradient in relation to

current density was calculated (fig. 6) from thecombined effects of voltage gradient and current.density (fig. 4) and from the effect of current,density alone (fig. 5). Mortality is shown to beproporl,ional to the voltage gradient. The relativeinfluence of voltage gradient and current densityunder the experimental conditions is illustrated bythe insert in figure 6.

During the tests, the fingerlings were held inuniform alinement with the direction of the elec­trical field (see Procedure). This subjected thelonger fish to a greater difference in potential.When the data shown in figure 4 are replotted interms of the total voltage to which the fish weresubjected (fish length X voltage gradient), they

80

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2 3 4 5 6 7 8 9 10 II

VOLTAGE GR ADIEN T(VOL TS/CM.l

FIGURE 6.-Effect of voltage gradient in relation to current density upon mortality of salmon fingerlings (Oncorhynch·ltstshawytscha) exposed to pulsating d. c. calculated (see insert) from the combined effects of voltage gradient and currentdensity (fig. 4) and the effect of current density (fig. 5).

MORTALITY OF SALMON IN PULSATING CURRENT 69

indicate that the shorter fish are actually affectedto a greater degree (fig. 7).

To determine whether the voltage gradient orthe total voltage to which the fish were subjectedwas the effective factor, a group of tests was madewith silver salmon (0. kisutch) in which the mor­tality of fingerlings alined parallel to the electricalfield was compared with the mortality of finger­lings alined perpendicular to the field. Evidence(table 3) that the total voltage to which the fishwere subject,ed is the effective factor in mortalitywas very conclusive. Electrical conditions thatproved fatal to 77.6 percent of the fingerlingsalined parallel to the field had no discernible injuri­ous effect on fingerlings alined perpendicular tothe field.

Experiments made to examine the effect of du­ration of exposure upon fingerlings subject,ed topulsating d. c. in relation to the combined influenceof voltage gradient and current density are sum­marized in figure 8, and the numerical data areshown in table 4. During these tests, pulse fre­quency, pulse duration, water temperature, waterresistance, and fish length were maintained con­stant. Similar experiments examining the effectof duration of exposure in relation to currentdensity alone are shown in figure 9, and the nu­merical data are listed in table 5. In these tests,pulse frequency, pulse duration, voltage gradient,water temperature, and fish size were held constantwhile the resistance of the water was modified.

70

76FISH

60LENGTH • I Q.•••••• 5CM . QQ. /___ 7 n . "

i='.. ,..

9 " . ,..'.67. v·

Z DDOD II " : / vQ >-

W : QQ f-e..:> 50 . U5N:.

/ 00a::: . z:2:.00W . WO. 0.a.. . / 00 0 ......

.57 en. 00. a....00 :2:.

/>- 40 .. <>'> f-~f- .. 0'> z:::l- · /....J · 00· w-~

.0

0 a:::~../ .48. 00 0::.

0:: 30.

00 :J.0 . e..:>.

/,>0

:2: : 0. ,0../

o~.. 0. 0"..3820 .

000.

/.:: 0

0

: / ••••••••../

..10 : ,29:

00

/ 00

0

0000

020 40 60 80 100 120 140 160

TOTAL VOLTAGE TO WHICH FISH WERE SUBJECTED(FISH LENGTH X VOLTAGE GRADIENT)

FIGURE 7.-Effect of the total voltage to which the fish were subjected in relation to fish length and current density upon. mortality of salmon fingerlings (Oncorhynchu8 tshawyt8cha) exposed to pulsating d. c. (fig. 4 replotted in terms of the

total voltage to which fish were subjected).

70 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

TABLE 3.-Relative effects of voltage gradient and total voltageto which fish were subJected on mortality of salmon finger­lings (Oncorhynchus kisutch) exposcd to pulsating d. c.

[Tests run at 811UI!'es/sec.• pulse duration 40 milliseconds, water temperature16.5° C., duration of exposure 1 minute; fish length, 7 em.]

Voltage TotalFish alinement rrla- gradient voltage Number Number Mor-

tive to electri~al (voltsl to which exposed dead talityfield fish were (percent)cm.) subjected

------------ParalleL ______________ 6 142 107 83 77.6Perpendicular_________ 6 -6 105 0 0

I Fish length X vnltage gradient.- Fish width X voltage gradient.

The results of both groups of experiments indi­cate, as would be expected, that the mortality offingerlings exposed to pulsating d. c. is propor­tional to the duration of exposure. The resultsfurther suggest that the effect of voltage gradientincreases with the duration of exposure while theeffect of current density may actually decreasewith an increase in duration of e."'{posure. How­ever, because of the scatter in the data, additionalevidence should be obtained to substantiate thislatter conclusion.

TABLE 4.-Ejj'ect of duration of exposure in relation to the combined e.ffect~ of volt{l.ge gradient and currellt ,jcn.~ity on 1/Iortal-ity ofsa.lmon fingerlings

Fish exposed to-

Duratioo of exposure 1 v./cm. and 0.05 ma/em.- 2 v./em. and 0.10 ma/em.- 4 v./em. and 0.19 ma./em.-

Numberexposed

Number Mortality Numberdead (percent) exposed

Nnmberdead

Mortalit;v(percent)

Numberexposed

Number Mortalitydead (percent)

0.5 min • . __ .______ __ 241 3 1.21 min • ___ 198 9 4.52 min • • • • • ._ _ 179 8 4.53 min • ._ 31 0 0 84 7 8.3

::~::::::::::::::::::::::::::::::::::::::: :::::::::::: :::::::::::: :::::::::::: ~ ~ g.4 ----- ----9S' -- -- --- --i2- ------- -i2~36 min • _. •__ __ __ __ __ 99 17 17.27 min • • • .____ 99 19 19.27.5 min_____________________________________ 52 6 11.5 •• _8 min • • • • • 142 38 26. 89 min • .____ 129 41 31.810 min •__.__________ 37 12 32.4 125 65 52.011 min • • • .__________ 23 ~ 39.112 min. • • . •• . .. 25 12 48.013 min • • •__ _ __ _____ 17 13 76.515min • .__________________ 4S 1 2.1 20 6 31).0 _20 mln •• 117 20 17.1 __ . . _

TABLE 5.-EjTr>ct of duration of exposure in relation tocurrent density /)/1. mortality of salmon fingerlings

Fish exposed to-

Duration 0.10 ma./em.- e.17 ma./em.-of

exposureMor-Number Number Mor- Number Number

exposed dead tality exposed dead tality(pereent) (percent)

---------------2 min____ • __

-------~.- ---------- ---------- 46 2 4.43 min_______ .'is 2 3.5 40 3 6.13.5 mln_____ 45' 1 2.2

-·----43~64 mln_______ 27 3 11.1 16 75 min_______ 67 9 13.2 55 15 36.87.5 min_____ 65 21 32.2 19 11 58.010 mln___ . __ 27 16 59.3 25 12 48.0

PULSE FREQUENCY

The effect of pulse frequency in relation tofish length upon mortality of fingerlings e."'{posedto pulsating d. c. was examined experimentallyby subjecting fingerlings of different lengths toa range of pulse frequencies while t.he voltagegradient, current density, pulse duration, watertemperature, and the duration 'of e."'{posure re­rnll.ined const.ant.

The data summarized in figure 10 (numericaldata shown in table 6) reveal that the mortality

MORTALITY OF SALMON IN PULSATING CURRENT 71

80

VQTAGE GRADIENT

. 70 e- 4 VOLTS leM..6.-2 "11- I

60

I-Z 50w00::WQ..

40

>-f-,-

::i 30<l:I-0::0:2:

20

10

•

OL...S!!:....:..----I~::.._--" -----L.---l..---.l...---'--...::~....l.---...!---..l--J

2 4 6 8 10 12 14

DURATION OF EXPOSURE(MINUTES)

16 18 20

FIGURE 8.-Effect of duration of exposure in relation t.o the combined effects of voltage gradient and current density uponmortality of salmon fingerlings .(Oncorhynchus tshall'y/scha) exposed to pulsating d. c. Tests run at 2 pulses/sec.,pulse duration 20 millisecs., t.emperature 10.00 to 1\.1.90 C., fish length 7 cm. Sizes of symbols corrl'spond to fish numbercnt.egorJes: 17-49,50-90, 100-199 and 200-241.

of salmon fingerlings esposed to pulsating d. c.increases with the pulse frequency and that theeffect of pulse frequency upon mortality increll.seswith the length of the fingerlings.

The relation of pulse frequency to the effect ofduration of exposure was explored in the group oftests summarized in figure 11 (numerical data

are shown in table 7). Fingerlings were exposedto a pulsating d. c. field for v~uious lengths oftime at two differe.nt pulse frequeucies while thevoltage gradient, current density, pulse duration,and water temperature were held constant. Theeffect of pulse frequency upon mort,ality wasfound to increase with the durnt;ion of exposure.

72 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

70CURRENT DENSI TYe- .17 MILLIAMPS I"CM~11- .10 " "

60

l- •ZUJ(j 500::W •fS

•>- :40I-::J •«I-er:: !300~

20

10

•0L.-_.G...L__-.L.__~__...L-__1..-_--1__-.L.__...L-__...L-__.1-_---I

109832 456 7DURATION OF EXPOSURE

(MIN UTES)

FIGURE 9.-Effect of duration of exposure in relation to current density upon mortality of salmon fingerlings (Oncorhynchustshawytschu) exposed to pulsating d. c. Tests run at 2 volt.s/cm., 2 pulses/sec., pulse duration 20 miIIisecs., tempera­ture range 10.0° to 19.9° C., fish length em. Sizes of symbols correspond to fish number categories: 16--49 and 50-65.

PULSE DURATION

To study the relation of pulse duration to theeffect of duration of exposure upon the mortalityof fingerlings exposed to pulsa,ting d. c., tests wererun in which fingerlings were subject,ed to differentpulse durations while the voltage gradient andcurrent density, pulse frequency, water tempera­ture, and fish length were held constant. On theirface, the data, gra!)hically shown in figure 12 andnumerically presented in table S, suggest thatpulses of long dura.tion may be less injurious thanpulses of short duration.

Since the tests with the 20-millisecond pulseduration and the tests with the SO-millisecondpulse duration were made several days apart andwith fish from two sources, an experimental checkwas made (see circle, fig. 12) testing fish from onlyone source on the same day. Fingerlings used inthis e.~periulental check were from the group offish used in the SO-millisecond pulse-durationtests. The results of the check fall along thetrend of the SO-millisecond pulse-duration tests,indicating that the difference shown between thereaction to the 20-millisecond and to the 80­millisecond pulse duration is probably due to

MORTALITY OF SALMON IN PULSATING CURRENT

80

FISH •70 .LI::NGTH

A-5CM.• -7 " •• -9 "*-11"

60

t- 50 ...ZLLI(.)0:::LLIa. 40>-I-...J<[

30'I-0:::0~

20

10

73

O'--__""-_:::::;..-~--...L...---..J---...L.---...I...---_e_--....L.-----J

2 4 6 8 10 12

PULSE FREQUENCY(P U L S E S / S EGO N D)

14 16

FIGURE 1O.-Effect of pul"e fl'cquency in relatioll to fu;h leugth upon mortality of salmon fingerlings (Oncorhynchustshawytscha) exposed to pulsat,ing d. c. Tests run at 4 volts/cm., current density range 0.15 to 0.27 milliamps./cm.2

,

pulse duration 20 millisecs., temperature range 10.0° to Ill.go C., duration of exposure 30 seconds. Sizes of symbolscorrespond to fish number categories: 10-49, 50-99, and 100-199.

74 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

TABLE 6.-Effect of 1mlse frequency in relation to fish length on mortality of salmon fingerlings

Fish length of-

Pulse !requeney 4 to 5.9 em. 6to 7.9 em. 8 to 9.9 em. 10 to 11.9 cm

Number Number Mortality Number Number l\Iortality Number Number Mortality Number Number Mortalityexposed dead (percent) exposed dead (perccnt) exposed dead (percent) exposed dead (percent)

---------1------------------------------------

------i25- --------s- ------6:4- -------26- --------5- -----i9~2- -------i2- --------4- ------iiii~ii

------iiiii- --------s- ------6~0- -------iio- -------i5- -----5ii~0- -------is- --------9- ------oo~o

------iss- -------i4- ------S~9- -------27- -------iif -----48~2- -------i5- -------ii- ------7ii~ii

I~ 3l ~:g -------ii5- -------25- -----7i~4- :::::::::: :::::::::: ::::::::::Ira 4~ g7.6 -------27- -------is- -----iiii~7- -------i2- --------ii- ------7~O

3 pulses/sec.___________________ 92 1 1.14 pulses/sec____________________ 10 0 05 pulses/sec___________________ 187 3 1.66 pulses/sec.__________________ 29 1 3.67pulses/sec___________________ 107 2 1.88 pulses/sec___________________ 77 1 1.310 pulses/sec__________________ 199 17 8.512 pulses/sec__________________ 14 4 28.613 pulses/sec__________________ 9S 11 11.214 pulses/sec . _15 pulses/sec__________________ liS 24 13.5

59 2 3.4 26 2 i.7 16 6.3

80

70

PULSEFR"EQUENCY11-8/ SEC •• -2 II

60•

-I-Z 50w ..<.)0::Wa..- 40>-I-::::i<[I-

300::0:2

20

•

10

0'--"'"&--L.-'--__-'--_--£.....L-__....L..-__-'-__-L-__....J..__-1-__--'-__---l__--1

10932" 4 5 6 7 8

DURATION OF EXPOSURE(MINUTES)

FIGURE 11.-Effcet of duration of exposure in relation to pulse frequency upon mortality of salmon fingerlings (Oncorhyn­chus tshawytscha) exposed to pulsat.ing d. c. Tests run at 2 volts/em., current density range 0.08 to 0.13 milliamps./em.2, pulse duration 20 millisecs., temperature range 12.0° to HI.9° C., fish length 9 em. Sizes of symbols correspondto fish number categories: 27-49, 50-99, and 100-111.

MORTALITY OF SALMON IN PULSATING CURRENT 75TABLE 7.-EjJect oj duration oj f!!Xposure 2'n relation to pulse

Jrequency on mortality oj salmon fingerlingsTABLE 8.-EjJect oj dura·tion oj expoS2tre in relation to pulse

duration on mortality oj salmon fingerlings

----1------------------Number Number Mortality Number Number Mortalityexposed dead (percent) exposed deed (percent)

Flsb exposed to pulse frequency of-

0.5 mln _1.0 min _1.5 min _2.0 min _2.5 min _3.0 min_____ 69 3 4.43.5 min_____ 101 10 9.95.0 min_____ 171 19 11.17.5 min_____ 69 21 30.410.0 min____ 36 21 58.3

Fisb exposed to pnlse duration of-

Duration 20 milliseconds 80 millisecondsofexposure

Nnmber Number Mortality Number Number Mortalit5exposed deed (percent) exposed deed (percent

---------0.5 min_____ 71 0 0 -------50- --------2- -------4~ii1.0 min_____ 14 0 01.5 min_____ 56 11 19.6 49 5 10.12.0 min_____ 46 8 17.4 48 7 14.62.5 min_____ 58 28 48.2 -------45" -------i7- ------37~83.0 min_____ 15 8 53.3

o3.1

13.316.348.337.5

o2

148

2824

8 pulses/sec.

7165

105496864

2 pulses/sec.Durationof

exposure

70PULSE DURATION.-'20 MILLlSC:CONDS• -80 II

60

4

I- 50zw~W0... 40

>-I-...J« 30I-0::a~

20

2 3

D U RAT ION -0 F EX P 0 S.U R E(M I NUT E S)

FIGURE 12.-Effect of duration of exposure in relation to pulse duration upon mortality of salmon fingerlings (Oncorhyn­chus tshawytscha) exposed to pulsating d. Co Tests run at 2 volts/cm., current density 0.10 milliamps./cm.l , 8 pulses/sec.,temperature range 10.0° to 16.0° C., fish length 9 em. For explanation of circled data see text. Sizes of symbolscorrespond to fish number categories: 14--49 and 50-58.

o

10

76 FISHERY BULLETIN "OF THE FISH AND WILDLIFE SERVICE

variation in condition of the two groups of fish.Therefore, the data are interpreted (as shown infig. 12) to mean that under the conditions of thesee:\:perirnents the pulse duration has no relation tothe effect of the duration of exposure upon mor­tality of fingerlings exposed to pulsating d. c.

An examination of the data thus interpreted

shows that the mortality of fingerlings exposed toa pulse duration of 20 milliseconds at a frequencyof 8 pulses per second (power on 16 percent of thetime) is equal to the mortality of fingerlings ex­posed under sinlilar conditions to a pulse durationof 80 milliseconds at a frequency of 8 pulses persecond (power on 64 percent of the tinle). It is

80

• •FISH

LENGTH70 A-5CM.

• -7 ".-9 "*-11. II

60r-zwL)

500:::Wa...

>- 40r--..J«r-0::: 300~

20

10

O"'"-ll~--'------'----~---'------'----~---'------'---'

142 4 6" 8 10 12

DURATION OF EXPOSURE. ...

~MIN UTE S)FIGURE 13.-Effect of duration of exposure in relation to fish length upon mortality of salmon fingerlings (Oncorhynchu8

tshawytscha) exposed to pulsating d. c. Tests run at 4 volts/em., current density range 0.14 to 0.27 milliamps./em.2,

2 pulses/sec., pulse duration 20 millisees., temperature range 15.0° to 19.9° C. Sizes of symbols correspond to fishnumber categories: 11-49, 50-99, and 100-154.

MORTALITY OF SALMON IN PULSATING CURRENT 77TABLE g.-Effect of dllration of exposure in relation to fish length on mortality of salmon fingerlings

Fish length of-

DuratioD of exposure 4 to 5.9 em. 6 to 7.9 em. I S to 9.9 em. I 10 to 11.9 em.

I I I I I·Number Number IMortalitY Number INumber MOItnlitYI Numbe·r Number MortalitYI Number Number Mortalityexposed dead (percent) exposed dead (perceut) exposed dead (pereeu t) exposed dead (percent)

--------·1------------------------------------0.5 miD_______________________ 92 0 0 154 2 1.3 115 3 4.6 56 3 5.4I.omin II__________ 1:!6 S 6.3 93 S 8.5 • _2.0 miD_______________________ 122 7 5.7 105 25 23.8 • _3.0miD • 77 7 9.1 21 5 23.8 11 2 18.24.0 mID • . _5.0min 29 2 Ii, 0 71 11 15.5 19 13 68.3 16 12 75.06.0miD ._____________ 18 3 16.7 68 14 20.6 18 11 61.2 14 9 64.27.0 miD .__ 31 4 12.9 76 18 23.7 20 12 00.0 14 10 71. 58.0 min_______________________ 26 8 30.8 113 33 29.2 21 13 61.9 _9.0min_______________________ 25 8 32.0 99 35 35.3 17 9 52.9 _10.0 min .________ 12 6 50.0 99 54 54.6 20 L1 11-1.9 _11.0 mln . .__________ 23 9 39.1 _

!U ~rn~~~~~~~~~~~~~~~~~~~~~l~~~~~~~~I~~~~~~~~~~I~~~~~~~~~~ -------~:- -------~:- -----::~~- ~~~~~~~~~~ ~~~~~~~~~~ ~~~~~~~~~~ ~~~~~~~~~~ ~~~~~~~~~~ ~~~~~~~~~~

14°

18°

•• ··5 eM.-":"7 "--9 "

FISH LENGTH

5 MIN.4

...... f~18·~• l80 FISHl 014.o

3

40

80%/220

01-'"..,<ll

10

20

30

60

50

70

80

• ISO••

'1-'.-<C'Cj. •

~:...- " leo..- /"""..-,/

./~:.-­

..,~.., ......",,,, ...

"," .."." .-

'0 fi;'..jSJ....... •••.).fJ"'J,-.:-' ._.

// ..,/.- __ ......... 14·

'/. •• 49 f\S,!}_---- •••.- ~----.-.",/ .- --- ..-,... .- ------- ....

~ _",...... _._-- fi;\"''''~••••.- .- __-----:-;- \'l.1.&•••

_/ --~--.- ....-- ~-- . .------- ..- .Ol----------------=-------=---------------l2 3 4 5 6 7 8 9 10

DURATION OF EXPOSURE(MINUTES)

FIGURE 14.-Effect of duration of exposure in relation to temperature and fish length upon mortality of salmon fingerlings(Oncorhynchus tsha.wytscha) exposed to pulsating d. c. Tests run at 4 volts/cm., current cIenl'lity range 0.14 to 0.27milliamps./cm.2, 2 pulses/sec., pulse duration 20 millisecs. (Insert: tests rUIl at 2 volts/em., current density range 0.09to 0.11 milliamps./cm.2, 2 pulses/sec., pulse duration 20 millisecs., fish length 9 em.)

i='zw<.)0:::Wc..~

.>­t-..J 40.«t-rr:o~

78 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

TABLE IO.-Effect of duratitm of eXpOSltre in relation to telll.perature and fish length on mortality of salmon fingerlings

Fish length oC-

Duration or exposure

Numberexposed

4 to 5.9 em.

Number Mortalitydead (percent)

Numberexposed

6 to 7.9 em.

Numberdead

Mortality(percent)

Numberexposed

8to 9.9 em.

Numberdead

Mortality(percent)

1 minute:14° C • • • •• _ 15 0 0 83 1 I. 2 100 0 018° C • •• 16 0 0 115 8 7.0 84 8 9.5

2 minutes:14° C ._._•• _._________ 12 0 0 77 2 2.6 67 8 11.9ISO C • •• .__ '4 0 0 102 6 5.9 98 22 22.5

3 minutes:14° C •• ._. • • 110 0 0 27 0 0 3 0 018° C •• • ._. .___________ 18 0 0 57 7 12.3 19 5 26.3

4 minutes:14° CISO C===:===::==:===:=:=========:======= ==========:= ====:=:=:=== =:========== ==:===:==:== :===:::::::: :====::=:::: ----------6- ----------2- --------33~3

5 minutes:14° C • .____ I .~2 0 0 21 1 4.S 4 1 25.0ISO C ._____________________ 21 2 9.5 51 11 21. 6 17 12 70.6

6 minutes:14° C __ • __ • • • ._ 55 2 3.6 53 8 15.1 3 1 33.3ISO C : • •• •• 12 2 16. 7 46 9 19. 6 5 3 60. 0

7 minutes:14° C • •__ •• • • flO I 1.7 48 4 8.3 2 0 0lSoC • ••• • 17 3 17.7 51 15 26.4 19 12 63.2

8mlnlltes:14° C. __ . . .___ 47 3 6.4 52 9 17.3 2 1 50.0ISO C __ • • •• 20 8 40.0 90 26 28.9 20 13 65.0

9 minutes:14° C___________________________________ 51 6 11.8 4S II 22.9 11 I 100.018° C_. • • • • •••• 13 5 38.5 81 30 37.0 17 9 52.9

10 minutes:14° C ._. __ ._____ 13 2 26.3 40 21 52.5 6 I 16.718° C • • __ ._. II 6 54.6 85 44 51.8 15 12 80.0

I Data not included in calculation or curves.

concluded that pulse duration is not a lethal fac­tor, at least within the range of conditions a",am­ined, and that there is no direct relation betweenmortality and the total energy applied per unit oftime.

FISH LENGTH AND DURATION OF EXPOSURE

The relation of fish length to the effect of dura­tion of a"'posure upon the mortality of chinookfingerlings exposed to pulsating d. c. was exam­ined in a series of experinlents in which fingerlingsof different lengths were subjected for variousperiods of time to a pulsating electrical field withvoltage gradient, current density, pulse frequency,pulse duration, and water temperature heldconstant.

The data graphically presented in figure 13 andnumerically shown in table 9 indicate that theeffect of duration of exposure upon mortality in­creases with the length of the fish.

TEMPERATURE

The relation of water temperature to the effectof duration of exposure on the mortality of chinookfingerlings subjected to pulsating d. c., was demon­strated b.v a group of experiments in which finger­lings of different lengths were subjected to pul-

sating d. c. at different water temperatures forvarious lengths of time. During these tests, volt­a.ge gradient, current density, pulse duration, andpulse frequency were held constant.

The data graphically shown in figure 14 andnumerically presented in table 10 reveal that abovea certain threshold exposure the influence of watertemperature on the mortality of chinook finger­lings exposed to pulsating d. c. increases with theduration of exposure and that the influence ofwater temperature upon mortality is greater uponlonger fish. The pattern of response was verified(see insert, fig. 14) by testing fingerlings from asingle source on the same day. The curves shownin the insert illustrate the greater effect of watertemperature at higher temperature levels. Themarked difference in mortality related to temper­ature in the current density a",periments (fig. 5),where exposure to the electrical field was only 30seconds, may have been due to the higher temper­ature levels involved.

DISCUSSION

The results of these experiments are in generalagTeement with the findings of other researchworkers investigating the effect of electric currenton fish. McMillan's (1928) a",periments with a. c.

MORTALITY OF SALMON IN PULSATING CURREN'.I," 79

showed an increase in mortality with an increasein voltage gradient and current density and withan increase in the duration of exposure. Similarresults were obtained in the present study withpulsating d. c. That the total voltage receivedby the fish is the effective factor rather than thevoltage gradient has been pointed out severaltimes in the literature (Okada 1929, Bramsnaeset al. 1942, Kuroki 1951). The evidence indicatingthat shorter fish are affer,ted to a greater degreeby total voltage than longer fish (fig. 7) agreeswith the findings of Kuroki, whose conclusionswere based on a study of the reactions of Garassiu,sallratllS in approximately the same length raugeas those used in this study.

There is some evidence suggesting that the rela­tion of fish length to the influence of total voltageupon mortality may be a function of the durationof exposure. Figure 7 indicates that shorter fishare more affected by the total voltage than longerfish when the exposure is only 30 seconds. Acomparison, in terms of the total voltage to whichthe fish were subjeeted, of mortality of fingerlingsof different lengths subjected to pulsating d. c.under almost similar conditions at eXl)osures of 4minutes and 8 minutes (figs. 8, 11, and 13), sug­gests that the relation may reverse with increasedexposure. At a 4-minute exposure the effect oftotal voltage is approximately equal for fish of7-cm. and 9-cm. lengths while with an 8-minuteexposure the longer fish are affected to a greaterdegree. The data, however, do not make clearwhether the increased mortality of the longer fishis due solti'ly to the greater effect of total voltageupon longer fish with increased duration of ex­posure or to the increased effect of some otherfactor such as pulse frequency.

In several of the experiments that showed asignificant relation between mortality and fishlength (see figs. 10, 13, and 14), the difference inmortality related to fish length was greater betweenthe 7-cm. and 9-cm. lengths than it was betweenthe 7-cm. and the 5-cm. lengths or between the9-cm. and the l1-cm. lengths. This suggests thepossibility that the difference in mortality mayalso be a function of some other aspect of the sizeof fish such as the cross-sectional area of the body.

One of the relations brought out by the experi­ments is the influence of water temperature uponthe mortality of fingerlings exposed to pulsatingd. c. The importance of water temperature,

apart from its effect upon the resistance of ,vater,is clearly shown by the marked increase in mortal­ity occurring under similar electrical conditionswith an increase of a few degrees in water temper­ature (see figs. 5 and 14). The B."\:perience ofLarimore, Durham, and Bennett (1950) in stunningfish with an electric fish shocker indicates that theeffect of temperature upon mortality shown inthe laboratory experiments will also be found inthe field. Larimore et a1 found that during coldweather the speed of their collecting operationwas slowed down because a longer B."\:posure wasrequired to stun the fish.

Since pulse duration does not appear to be alethal fact,or and since there does not appea,r to bea direct relation between mortality and the totalenergy applied per unit of time, as contrastedwith the marked effect of pulse frequency uponmortality, the evidence points to the probableimportance of wave form. If the increasedmortality caused by an increase in pulse frequencyis not due to the increase in total energy appliedper unit of time, it must be due to the increase ir..the number of changes in potential. If change inpotential is the effective factor, then the rate ofchange in potential should be of great importance.

The relation between mortality of the fish sub­jected to pulsating d. c. under the experimentalconditions just described and mortality of wildfish subjected to pulsating d. c. under naturalstream conditions must remain a matter of specula­tion until it is examined experimentally. Differ­ences in the condition of wild fie.;h and of hatcheryfish might result in a marked difference in theirability to withstand subjection to electric current.The definition of mortality used in the laboratoryexperiments allowed 1 hour after exposure forrecovery, during which time the fingerlings wereheld in aerated glass bowls. Whether the propor­tion of recoveries would be as great or 'greaterunder stream conditions where factors such asturbulence and predation would be in operationduring that hour is open to conjecture.

In general, one might expect the greater mor­tality under the laboratory treatment. Thefingerlings had to be netted several times, trans­ported, held in tanks, and subjected to severalcomplete water changes. During their exposureto the electrical field the fish were restricted byplastic stalls, and this may have resulted in somemechanical injury due to violent movements when

80 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

the current was first applied. The fingerlingswere always held in alinement parallel to thedirect·ion of the elect,rical field (the one exceptionis noted on p. 69) and would therefore be con­tinually subjected to a maximum voltage. In astream the free-swinlllling fish mny be nlineddirectly parallel to the field for only n part of thetotal exposure.

Interpretation of the data from these laboratoryexperiments for use in electrieal fish-guiding ex­periments in the field must take. into considerationother factors as well. The maximum width of adirectional electrified zone that could be usedwould be determined by the rate at which the fishswim out of the eleetrified zone and by the maxi­mum duration of exposure that is "safe" for thefish. Assuming that the fingerlings are dis­tributed at random throughout the stream, onlythose fish entering at t,he extreme negative end ofthe electrified zone would be subjected t,o theentire width of the zone in moving to the positiveend. Thus, a 15-percent expected mortality forthose fish exposed to the ma.ximum field widthmay represent only a negligible mortality in termsof the total number of fish being directed by theelectrified zone. It may be possible to safelydirect fingerlings in ranges of electrical conditionswhich produced a mortality of 30 or 40 percent inthe laboratory experiments. One of the tasks offield experiments in electrical fish guiding will beto determine the relation between mortality understandardized laboratory conditions and thatunder conditions in the stream.

The experiment~ reported here emphasize onepoint'-a significant part of the ranges of electricalcharacteristics desirable in fish guiding are lethalto some degree for salmon fingerlings. The pos­sibility of injurious effects of a nonvisible nature(e. g., an effect, upon reproductive ability) is beingexplored. .Although this study is not yet com­plete enough to draw many conclusions, it is clearthat the application of the principle of electro­taxis to the protection of salmon fingerlings willrequire an intinlate knowledge of the relationbetween the electrical-energy levels producingelect,rotaxis and t,hose detrimental to the fish.

SUMMARY

The influence of voltage gradient, current den­sity, pulse frequency, nnd duration of exposure

upon the mortality of salmon fingerlings exposedto pulsating direct current was e..~amined experi­mentally in relation to the length of fish, watertemperature, and pulse duration. A current ofsquare-wave form was used and the followingranges were explored: Voltage gradient, 0.5 to 15volts/cm.; pulse frequency, 2 to 15/sec.; pulseduration, 20 to 80 milliseconds; current density,0.05 to 1.9 milliamps./cm.2

; duration of exposure,0.5 to 20 minutes; fingerling lengt,hs, 4 to 12 cm.;and temperature, 10° to 25° C.

For simplification, the assumption was madethat a straight line of regression was the mostsatisfactory description of the relations examined,and the results of the experiments, above thresholdvalues, were interpreted as follows:

1. Mortality increased in a constant ratio withan increase in voltage gradient, an increase incurrent density, or an increase in both. Theeffect of voltage gradient increa.sed with the dura­tion of exposure.

2. The total voltage to which the fish were sub­jected (i. e., fish lengthXvoltage gradient) wasthe effective factor in mortality rather than thevoltage gradient, and the effect of total voltage

.upon mortality was actually greater on the shorterfish when the exposure was only 30 seconds.

3. Fingerlings exposed to a pulse of 20 milli­seconds at, a frequency of 8/sec. (power on 16 per­cent of the time) had the same mortality as finger­lings exposed linder similar conditions to a pulseof 80 milliseconds duration at a frequency of 8/se.c.(power on 64 percent of the time), indicating thatunder the conditions of the experiment pulseduration was not a lethal factor and that therewas no direct relation between mortality and thetotal energy applied per unit of time.

4. Mortality increased with the pulse fre­quency, and the effect of pulse frequency uponmortality increased with the length of fish andthe durat,ion of exposure.

5. Mort,ality of fingerlings' exposed to pulsatingd. c. increased with the duration of exposure, andthe effect of dUl'l1tion of exposure increased withthe len~th of the fingerlings.

6. Mortality increased with the water tem­perature, ltnd the effect of water temperatureupon morta.Iit.y inc-reased· with the duration ofexposure. The effect of water temperature uponmortality was greater on fish of greater length.

MORTALITY OF SALMON IN PULSATING CURRENT 81

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1950. Electrical stimulation of fish in sea. wate-r.California Coop. Sardine Research Program, ProgressRept., pp. 46-47.

KUROKI, TOSHIRO.1951. Study on t,he electric fish screen. IV. The elec­

trifying effects by 10-4 sec. order low frequencyelectric shocks upon fish bodies. Bull. Japanese Soc.Sci. Fish., vol. 18, No.1 (1952), pp. 25-29. (Trans­lated from the Japanese by Akira Ishimaru.)

o

LARIMORE, R. \VELDON, LEONARD DURHAM, and GEORGEW. BENNETT.

1950. A modification of the electric fish shocker forlake work. Jour. Wildlife Management" vol. 14, No.3, pp. 320-323.

McMILLAN, F. O.1928. Electric fish screen. U. S. Bur. Fish. BUll., vol.

44, pp. 97-128.OKADA, MITUYO.

1929. On the action of electric current on fishes. Ex­citation and narcosis. Jour. Imperial Fish. Institut.e(Tokyo), vol. 24, No.2, pp. 64-72.

SCHEMINZKY, FERDINAND.1924. Versuche uber electrot.axi8 und electronarkose.

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