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

Abstract

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.

Impact of Pulsed Direct Current on Embryos, Larvae, and Young Juveniles of Atlantic Cod and its Implications for Electrotrawling of Brown Shrimp

“…Atlantic Cod eggs are relatively small (1.16-1.89 mm; Andersen et al 1994;Auditore et al 1994). As transmembrane potential increases with cell radius (Gaylor et al 1988), several studies have confirmed that electroshock-induced mortality increases with egg size (Henry and Grizzle 2004;Bohl et al 2010). Survival is known to decrease when voltage levels increase.…”

“…In this way, the appropriate number of embryos (15,000) or larvae (3,200) was transferred from the incubator tank to a plastic exposure chamber (33 × 24.5 × 21 cm) that contained 12 L of seawater ( Figure 1). Within the chamber, two plate-shaped, stainless-steel electrodes (32 × 23 × 0.4 cm) that conformed to the cross-sectional area of the chamber were fixed in parallel at 24.5 cm apart and were connected to the output of an adjustable laboratory pulse generator (LPG; EPLG bvba, Belgium ;Stewart 1972;Henry and Grizzle 2004;Bohl et al 2010). The LPG ( Figure 1) was set to produce a unipolar, square-wave PDC.…”

Pulse Trawling: The Impact of Pulsed Direct Current on Early Life Stages of Sole Solea solea

“…As mortality caused by electric pulses increases with egg size, a voltage gradient of 16 V/cm caused a significant decrease in survival for freshwater species with a comparable egg size of approximately 1 mm (Henry and Grizzle ; Bohl et al. ). In the present study, a lower voltage‐gradient intensity of 1.5 V/cm was applied in seawater, corresponding to the pulse used to catch brown shrimp at sea.…”

Electroimmobilization as an Alternative Method to Chemical Immobilization of Larval Fish

“…Previous electrofishing studies on both adult and younger life stages have shown that larger fish and larger‐diameter embryos tend to be more susceptible to electricity because a greater amount of surface area is exposed to the electric field (Dolan and Miranda ; Henry and Grizzle ; Bohl et al. ; Nutile et al. ); hence, more electric power is transferred through the body.…”