Electroshock-induced mortality in freshwater fish embryos increases with embryo diameter: a model based on results from 10 species

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.