Effects of electroshock on cyprinid embryos: implications for threatened and endangered fishes

The purpose of this study was to evaluate the effects of electroshock on survival to hatching in embryos of Cyprinidae, which includes numerous fish species designated as threatened or endangered under the U.S. Endangered Species Act. Embryos of three cyprinids were exposed for 20 s to a homogeneous electric field (DC or 60-Hz pulsed DC [PPDC], 3-ms pulse width) at voltage gradients similar to those used during electrofishing. Exposure occurred only once and was at a specific stage of development. Zebrafish Danio rerio were electroshocked at numerous stages of embryonic development, and the most sensitive developmental stage was determined and used to guide subsequent experiments. Embryos of two minnows native to the southeast United States, the spotfin chub Erimonax monachus and whitetail shiner Cyprinella galactura, were exposed to a range of DC (3-15 V/cm) and 60-Hz PDC (8-15 V/cm) voltage gradients, and survival to hatching was evaluated. Additionally, the potential for electrofishing to induce premature hatching in late-stage cyprinid embryos was investigated by exposing eyed spotfin chub embryos to 8-V/cm DC electroshock. Embryos were most vulnerable to electroshock-induced mortality early in development, particularly near epiboly, and DC was more harmful than 60-Hz PDC. At older developmental stages, embryos were less vulnerable to electroshock-induced mortality, although premature hatching was induced in some older developmental stages of electroshocked spotfin chub embryos. Whitetail shiner embryos were more vulnerable (lethal voltage gradient predicted to induce 50% mortality [LV50], 5 V/cm) to electroshock-induced mortality than were spotfin chub embryos (LV50, 6 V/cm). Results indicate that cyprinid embryos can be killed by DC electroshock at electric field intensities commonly generated by electrofishing equipment, and electrofishing near spawning grounds of threatened or endangered cyprinids should be avoided when embryos are present.