Susceptibility of ten fish species to electroshock-induced mortality

Ten species of fish were exposed to homogeneous electric fields of 60-Hz pulsed DC in water having an ambient conductivity of 100 muS/cm. A range of voltage gradients was used for the electroshock, and the percentage of fish dead after I It was determined. A logistic model was used to compare species, and the voltage gradient that was lethal within 1 h to 50% of the fish (LV50) was computed. Except for blackbanded darters Percina nigrofasciata (juveniles and adults) and western mosquitofish Gambusia affinis (adults), all fish were newly transformed juveniles. which for some species are more sensitive to the lethal effects of electroshock than are younger or older fish. The most susceptible species was the blackbanded darter (LV50 = 1.7 V/ cm), followed by largemouth bass Micropterley salmoides (LV50 - 3.0 V/cm), striped bass Morone saxatilis (LV50 = 4.0 V/cm), and channel catfish Ictalurus punctatus (LV50 = 4.1 V/cm). Species of intermediate susceptibility were the rainbow trout Oncorhynchus mykiss (LV50 - 5.7 V/cm), blue-ill Lepomis macrochirus (LV50 = 5.7 V/cm), and black crappie Pomoxis nigromaculatus (LV50 = 6.3 V/cm). Nile tilapias Oreochromis niloticus died only at the highest voltage gradient (27% mortality at 16 V/cm); paddlefish Polyodon spathula and western mosquitofish did not die after exposure to 16 V/cm. The wide variation in susceptibility to electroshock-induced mortality among species indicates that caution should be used in habitats where sensitive species are present.