of high-voltage AC current on trout mortality has not been documented. In this paper, I present data on (1) immediate mortality, (2) delayed mortality, and (3) ...
North American Journal of FisheriesManagement 5:475-479, 1985 ¸ Copyrightby the AmericanFisheriesSociety1985
Rainbow Trout and Brook Trout Mortality from High Voltage AC Electrofishingin a Controlled
Environment
MARK
HUDY 1
Georgia CooperativeFishery ResearchUnit: Universityof Georgia Schoolof ForestResources Athens,Georgia 30602 ABSTRACT
Twelve groupsof 250 hatchery rainbow trout (Salmo gairdnerOand brook trout (Salvellnus fontinaIls) were electroshocked in hatcheryracewaysand monitoredfor 15 days.The mean immediate, delayed, and total mortality was less than 2% at all alternating current voltagestested (350, 700, and 760 volts). Radiographsof survivingtrout showedthat only a small percentage
( 0.05, N = 12). Meannumberof mortalities Treat
ImmediateDelayed
Percent
Total mortality of
ment
RBT
BRK
RBT
BRK
RBT
BRK
all fish
Control 350 700 760
0.0 1.0 1.0 0.0
0.0 0.0 0.0 0.3
0.0 3.0 2.0 1.0
0.0 0.6 0.3 0.0
0.0 4.0 3.0 1.0
0.0 0.6 0.3 0.3
0.0 1.8 1.3 0.5
of variance,P > 0.05, N = 12)amongtreatment
meansfor rainbow trout and brook trout, or the combineddata from both species(Table 1). Only 28 of the 3,000 fish in the experiment died--7 immediatelyafter treatmentand 21 later during Electrofishing a 15-day period. Rainbow trout had a signifiTwo-man crews electrofishedeach raceway cantlyhigherpercentageof the mortalities(79%) three to four times in a manner similar to stream thanbrooktrout (Chi-square, P < 0.05, N = 28). electrofishinguntil all fish were removed. Cap- The combined total mortality for both species tured fishwere immediatelytransferredto hold- averaged0.0% (control),1.8%(350 v), 1.3%(700 ing racewaysto reducehandlingstress. v), and 0.5% (760 v). There were no significant The treatmentwith thelowestvoltagewasdone differences(t test, P > 0.05) in the mean length with a backpackelectroshocker having a maxi- betweeneither the living and deadrainbowtrout mum output of 350 v. A radio antenna served CN•= 100, N 2 = 22) or brook trout CN•= 100, as one probe and an aluminum hoop (50 cm in N2 = 6). At the conclusionof the experiment,all diameter) with an attachednet servedas the end fish were maintaining equilibrium with no apof the other probe.The unit was poweredby a parent stressexcept for a few which exhibited WeedeaterSV-3 enginewith a Tiny Tiger gen- abnormal swimming behavior. The number of survivors with a visible aberator model 5001-1 (capacity 350 watts maximum, 250 watts continuous,voltage 110 AC, normality (bum, erraticswimmingstyle)waslow, and a frequencyof 300 hertz).The sameequip- averaging0.0% (control),1.6%(350 v), 2.4% (700 ment was used for the next treatment which had v), and 0.8% (760 v). Betweenthe two species, a maximum output of 700 v. brooktrout had a significantly higherpercentage A backpackelectroshockerwith a maximum (72%) of abnormalities(Chi-square,P < 0.05, outputof 760 v wasusedfor the highestvoltage. N = 36). Aluminum hoops(25 cm in diameter) without The radiographsshowedthat only 21% (6 of nets served as the ends of the probes. The unit 28) of the dead trout had fracturedor dislocated was poweredby a TAS PortableEngineGener- vertebrae.However, 77% (27 of 36) of the abator (QEG 300, capacity 300 watts maximum, normal surviving fish had fractured or dislo250 watts continuous,voltage 110-115 AC, and cated vertebrae, the injury usually occurring somewhere between the 15th and the 25th aba frequencyof 250-300 hertz). dominal vertebrae(Figs. 1 and 2). Normal-apRESULTS pearingshockedfish had a 1% (1 of 96) level of The immediate, delayed,and total mortalities injured vertebrae and the control fish had no werelow with no significantdifferences(analysis injured vertebrae. Some fish from all treatments
TROUT MORTALITY FROM ELECTROFISHING
477
Figure 1. Radiographof a lateral viewof two brooktrout that exhibitedabnormalswimmingstyles after being electroshockedby 700 v AC. Note dislocatedvertebrae.
had fusedvertebraewhich probably were not causedby electrofishing(McCrimmon and Bidgood 1965: Gill and Fisk 1965). MANAGEMENT
IMPLICATIONS
thereason,thedifferences probablyweretoosmall to be of managementsignificance. The reactionsand representativesymptomsof dead and dying fish were similar to those re-
ported by Hauck (1949), and probably were Under the testconditions,all the high-voltage causedby eitherrespirationfailure,hemorrhagtreatments had a low percentageof mortalities ing, fracturedvertebrae,or the combined effects (
