Electroshocking-Induced Mortality of Four Fish Species during Posthatching Development

Abstract

Immediate mortality of electroshocked fish was related to the stage of development after hatching. Larvae and juveniles of four species of fish were exposed to homogeneous voltage gradients (2-16 V/cm) of 60-Hz pulsed DC in water having an ambient conductivity of 100 S/ cm. Recently hatched fish and fish older than 100 d did not die after electroshocking. The developmental period most susceptible to electroshocking-induced mortality was near the time of transformation from larvae to juveniles for all four species. The highest predicted mortality occurred 22 d after hatching or at 19-21 mm total length (TL) for bluegill Lepomis macrochirus, 36-41 d or 29-32 mm TL for largemouth bass Micropterus salmoides, 42-43 d or 27-30 mm TL for channel catfish Ictalurus punctatus, and 38 d or 21 mm TL for Nile tilapia Oreochromis niloticus. During a 5-d observation period, there was no delayed mortality of channel catfish. A field validation experiment with 25-d-old largemouth bass (14-22 mm TL) indicated that mortality in the laboratory or around an electrofishing boat did not differ if voltage gradients were similar.

Susceptibility of Ten Fish Species to Electroshock‐Induced Mortality

“…Delayed mortality is low (Ͻ10%) in most studies (Barrett and Grossman 1988;Habera et al 1996;Ruppert and Muth 1997;Cook et al 1998). In a previous paper, we reported that electroshocked channel catfish that were alive after 1 h did not die during the following 5 d, even though immediate mortality was 68% (Henry et al 2003a).…”

“…However, except for a comparison of two species by Whaley et al (1978), multiple-species comparisons of mortality after exposure to homogeneous electric fields have not been conducted. Laboratory experiments with homogeneous electric fields are useful for predicting the fish mortality caused by field electrofishing (Henry et al 2003a) and are appropriate for multiple-species comparisons of electrofishing-induced mortality.…”

“…Stage of development is related to electroshock mortality in some fish species (Henry et al 2003a); therefore, differences in life history stage should be considered in comparisons of electrofishing-induced mortality among species. In a study of four fish species, newly metamorphosed juveniles had higher mortality following electroshock than younger or older fish (Henry et al 2003a).…”

“…In a study of four fish species, newly metamorphosed juveniles had higher mortality following electroshock than younger or older fish (Henry et al 2003a). Studies of electroshock-induced mortality of older fish offer conflicting results, including higher mortality for smaller fish (Habera et al 1996), higher mortality for larger fish (Holliman et al 2003), or no difference in mortality with respect to fish size (Collins et al 1954;Pratt 1955;Whaley et al 1978).…”

Electrofishing Practices Have Limited Effects on Largemouth Bass Feeding Behavior

“…Electrofishing can, however, be lethal or injurious to collected fishes (e.g., BardygulaNonn et al 1995;Dalbey et al 1996;Dwyer et al 2001;Snyder 2003;Dolan and Miranda 2004;Schreer et al 2004) or their offspring (e.g., Dwyer et al 1993;Dwyer and Erdahl 1995;Henry et al 2003;Bohl et al 2009). A few studies have examined nonlethal effects of electrofishing practices and found decreased fish feeding and growth rates (Gatz et al 1986;Gatz and Adams 1987;Dalbey et al 1996), increased susceptibility to predation , and increased nest abandonment in brood-guarding species (Siepker et al 2006b).…”