Survival of largemouth bass, bluegill and channel catfish embryos after electroshocking
Survival to hatching was determined after electroshocking embryos of largemouth bass Micropterus salmoides, bluegill Lepomis macrochirus and channel catfish Ictalurus punctatus. Embryos at different developmental stages were exposed for 20 s to homogeneous electric fields (4–16 V cm−1) of direct current (DC) or 60 or 120 Hz pulsed direct current (PDC) in water of 100 S cm−1 ambient conductivity. For all species, DC reduced survival of embryos at developmental stages before, during, or soon after epiboly; but survival did not differ from controls during later developmental stages. Survival of largemouth bass and bluegill was not reduced by 60 or 120 Hz PDC except for bluegill exposed at 12 h post‐fertilization. Channel catfish embryo survival was <5% when exposed to 60 or 120 Hz PDC at 8 h post‐fertilization, survival improved for embryos exposed at 67 h to 60 Hz but not to 120 Hz, and all embryos survived exposure to PDC at 150 h post‐fertilization. Exposure durations as short as 5 s resulted in <10% survival of largemouth bass during sensitive stages. All bluegill embryos aged 22 h post‐fertilization hatched prematurely after exposure to 16 V cm−1 DC, but survival was not affected. The use of PDC for electroshocking near largemouth bass and bluegill nests could reduce the negative effects on survival of these species; however, PDC can reduce survival of channel catfish embryos.