Negative Effects of Electroshocking Fish Embryos: Implications for Threatened and Endangered Fishes

The purpose of this study was to evaluate the effects of waterborne electric fields on survival of fish embryos. Embryos can be exposed to electric fields during routine electrofishing operations aimed at collecting older fish life history stages to provide data for management of fish populations. Negative effects can occur in fish embryos after electric exposure and this is a particular concern if fish are threatened or endangered species. A primary objective of this study was to develop a model to assist in the prediction of effects of electrofishing on survival of fish embryos. In this investigation, fish embryos were electroshocked over a range of developmental stages to determine the most sensitive developmental stage. The most sensitive developmental stage was then used to assess the effect of current type and electric field intensity on survival and induction of premature hatching in electroshocked embryos. Embryos were most affected by electroshock 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, and, in some older developmental stages of spotfin chub Erimonax monachus, premature hatching was induced by electroshock. Evidence of premature hatching in other species was inconclusive. Of the species tested, rainbow trout Oncorhynchus mykiss were largest in diameter (4.9 mm) and most sensitive to DC electroshock (lethal voltage gradient causing 50% survival (LV-50) = 1.2 V/cm), followed by whitetail shiner Cyprinella galactura (1.77 mm; LV-50 = 5 V/cm) and spotfin chub (1.83 mm; LV-50 = 6 V/cm), which were similar in size and sensitivity. A strong relation between embryo diameter and vulnerability to electroshock-induced mortality was found when results from the present investigation were combined with similar results from the literature. Results support use of embryo size as a predictor of vulnerability to electroshock in other species, and indicate that species with large embryos may be particularly vulnerable to lethal effects of electrofishing.