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Influence of electroshock and mechanical shock on survival of trout eggs

, : Influence of electroshock and mechanical shock on survival of trout eggs. North American Journal of Fisheries Management 13(4): 839-843

Tests were conducted to determine if electric current applied by electrofishing equipment had an effect on trout egg mortality. Eggs of rainbow trout Oncorhynchus mykiss were exposed to a standardized mechanical shock and to electric current from a backpack electroshocker. To separate the effect of handling from the electroshock effect, one group of control eggs was handled the same as electroshocked eggs, but without exposure to electricity. Another control group was not handled at all. Samples of eggs were exposed to one of the three treatments on days 2, 4, 6, 8, 10, 12, 14, 16, 18, 22, or 26 postfertilization. The shocker output was measured at 0.6 A, pulse was 250 Hz, and the uniform voltage gradient in the exposure chamber was 0.9-1.0 V/cm. The most sensitive time in the development of the eggs to both mechanical and electrical shock was on day 8 postfertilization when incubated at 10.4 degree C; treatment at this time resulted in a mortality rate (determined on days 26-27 postfertilization) of 99% for mechanically shocked eggs, 57.9% for electroshocked eggs, and 29.8% among controls handled the same as the eggs that received the electroshock. The mortality of eggs that were not handled at all was 19.7%. Results from further tests with eggs of cutthroat trout O. clarki showed that the level of electric current used does have an effect on the survival of trout eggs. We also demonstrated that cutthroat trout eggs placed in artificial redds in a stream can be killed by the same level of current used in these tests. Our findings indicate that electrofishing over recently deposited trout eggs can increase mortality.


DOI: 10.1577/1548-8675(1993)013<0839:IOEAMS>2.3.CO;2

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