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 [PDC], 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.

The purpose of this study was to develop a model to predict electroshock-induced mortality in embryos of freshwater fishes. Herein, electroshock-induced mortality was evaluated for sauger Sander canadensis and rainbow trout Oncorhynchus mykiss, and results were combined with published results obtained for eight other species in studies that used consistent methodology. The model was based on embryo diameter (1·1-4·1 mm among species), the most sensitive stage of embryonic development (near completion of epiboly for all species), and mortality (to hatching or eyed stage) after exposure to a homogeneous electric field [direct current (DC) or 60 Hz pulsed DC (PDC)]. Embryo diameter was positively related to electroshock-induced mortality for DC (P < 0·001) and 60 Hz PDC (P < 0·05). Results suggested that vulnerability to electroshock-induced mortality was related to physical characteristics (i.e. size) of embryos rather than species differences, and indicated that prediction of vulnerability in untested species is possible. This is particularly important for protection of endangered species, and those species with larger embryo sizes may be at most risk from electroshock. Conversely, results also suggested that it may be possible to assist in removal of invasive non-native fish species with large embryo diameters (e.g. O. mykiss) by application of electroshock to target and kill embryos of these species in some freshwater habitats.