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r '" W/~#4/1IWJk'''.~WiJey 07/Q.../ \'11<6 Lethality of Electroshock to Two Freshwater Fishes Roy Allen Whaley Wyoming Game and Fish Departrnent, Casper District Casper, Wyoming 82601 o. Eugene Maughan Oldahoma Cooperative Fishery Research Unit Oklahoma State University, Stillwater, Oklahoma 74074 and Paris H. Wiley Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061 ABSTRACT: The lethality of electroshock to fish was examined by subjecting fantail darters (Etheostoma fZabellare) and bluegills (Lepomis macrochirus) to levels and patterns ofpulsating direct current electricity within the ranges commonly employed in the collection of fish in the field. Mortality of fish exposed to pulsating direct current increased with increased pulse frequency and exposure time. However, mor- talities were negligible among fish exposed for 15 s or less, regardless of the electrical characteristics. I I Electrofishing is one of the most common methods of collecting fish during stream surveys. Electrofishing usually kills few or no fish but Collins et al. (1954) found that certain electrical characteristics caused mortality of fish. Total voltage, for example, was a critical factor influencing mortality of fingerling chinook salmon (On- corhynchus tshawytscha). Increased pulse frequency also increased mortality, but pulse duration did not. O. E. Maughan and C. B. Schreck (unpublished data) found that, when fathead minnows (Pirnephales prorn- elas) were exposed to 160 V for up to 270 s, survival was inversely related to exposure time; a similar relation was observed in bluegills (Lepornis rnacrochirus). A knowledge of the lethality of electric shock to fish is particularly important to app-lied fishery biologists who use electrofishing to rnake depletion-based population estirnates because fish not captured during the first at- tempt must remain available for capture during later attempts (Everhart 1972). The reliability of the esti- mates becomes questionable if any uncaptured fish die from the initial shock. The present study was under- taken to deterrnine the levels and patterns of electricity that are lethal to two freshwater species offish, bluegills and fantail darters (Etheostorna flabellare). VOL. 40, NO.4, OCTOBER 1978 Methods - Experirnents were conducted from Decernber 1974 through February 1975 with fantail darters and bluegills. Darters were collected by seine frorn local streams and held in 38-liter aquariums for at least 3 days before each experiment. Bluegills were collected by trap from local ponds and held in a large holding tank at least 3 days before use. Experirnents were perforrned in a rectangular plastic aquariurn equipped with two flat, alurninurn plate elec- trodes suspended perpendicular to the long axis. Verti- cal stalls, 2 cm deep, 2 cm wide, and 7 cm long for the darters, and 10 cm deep, 4 cm wide, and 18 cm long for the bluegills, were constructed of thin plastic and wood. The stalls kept the fish aligned parallel to the electric field. Plastic screen at the ends of the stalls prevented fish frorn escaping when electric current was applied. Physical and chemical characteristics of the water in which the experirnents were conducted were as follows (SE in parentheses): ternperature, 10.0 (0.2) oC; dis- solved oxygen, 10.0 (0.5) mg!l; total hardness or CaC<h, 36.5 (1.2) mg/l; total dissolved solids, 60.0 0.4) rng/l; and conductivity, 154.0 (1.0) J..I.mho. 161