Electric‐induced mortality of newly transformed juvenile fishes in waters of different conductivity
In three experiments, each with three species of newly transformed juvenile fishes, the immediate mortality was determined after electrical exposure to 60 Hz pulsed DC in waters of different conductivity (Cw). With a constant applied power density (Da; 1·0–4·9 mW cm−3 depending on species) over a range of Cw(10–1020 μS cm−1), the results predicted that the highest fish mortality would occur at Cw of 65 μS cm−1 for bluegill Lepomis macrochirus, 74 μS cm−1 for largemouth bass Micropterus salmoides and at 140–175 μS cm−1 for channel catfish Ictalurus punctatus. In experiment 2, the voltage gradient (E) was maintained constant (2·5–8·0 peak V cm−1 depending on species) over the same range of Cw, and fish mortality increased with current density (J) or Da, which are directly related to Cw. In experiment 3, fish mortality did not differ when peak E(3 or 8 V cm−1 depending on species) and mean J(0·09 or 0·24 mA cm−2 depending on species) were held constant by changing pulse width in waters with different Cw(99, 165 or 495 μS cm−1). Fish mortality in this experiment was not significantly related to peak or mean transferred power density, and the ‘power transfer theory for electrofishing’ was not useful for predicting electrofishing mortality. Overall, the results of the present study indicated that mortality caused by exposure to electricity can be predicted more accurately with the variables peak E and mean J than with models requiring determination of effective conductivity of the fish.