Effects of Electroshock on Cyprinid Embryos: Implications for Threatened and Endangered Fishes

Abstract

The purpose of this study was to evaluate the effects of electroshock on survival to hatching in embryos of Cyprinidae, which includes numerous fish species designated as threatened or endangered under the U.S. Endangered Species Act. Embryos of three cyprinids were exposed for 20 s to a homogeneous electric field (DC or 60‐Hz pulsed DC [PDC], 3‐ms pulse width) at voltage gradients similar to those used during electrofishing. Exposure occurred only once and was at a specific stage of development. Zebrafish Danio rerio were electroshocked at numerous stages of embryonic development, and the most sensitive developmental stage was determined and used to guide subsequent experiments. Embryos of two minnows native to the southeast United States, the spotfin chub Erimonax monachus and whitetail shiner Cyprinella galactura, were exposed to a range of DC (3‐15 V/cm) and 60‐Hz PDC (8‐15 V/cm) voltage gradients, and survival to hatching was evaluated. Additionally, the potential for electrofishing to induce premature hatching in late‐stage cyprinid embryos was investigated by exposing eyed spotfin chub embryos to 8‐V/cm DC electroshock. Embryos were most vulnerable to electroshock‐induced mortality early in development, particularly near epiboly, and DC was more harmful than 60‐Hz PDC. At older developmental stages, embryos were less vulnerable to electroshock‐induced mortality, although premature hatching was induced in some older developmental stages of electroshocked spotfin chub embryos. Whitetail shiner embryos were more vulnerable (lethal voltage gradient predicted to induce 50% mortality [LV50], 5 V/cm) to electroshock‐induced mortality than were spotfin chub embryos (LV50, 6 V/cm). Results indicate that cyprinid embryos can be killed by DC electroshock at electric field intensities commonly generated by electrofishing equipment, and electrofishing near spawning grounds of threatened or endangered cyprinids should be avoided when embryos are present.

Using occupancy and species distribution models to assess the conservation status and habitat use of the goldline darter (Percina aurolineata) in Georgia, USA

“…Based upon simulation modelling, MacKenzie & Royle (2005) developed a table yielding the optimum number of surveys per site (K) for different combinations of occupancy and detection; optimum refers to a design that minimises variance in the occupancy estimate by balancing the trade-off between sampling intensively at a few sites or less intensively at many sites. This is important given the cost of sampling and the risk of mortality associated with electrofishing (e.g., Bohl et al 2009). Similarly, using our estimated values of p, w, K and equation 6.3 in MacKenzie et al (2006), the number of sites needed to achieve a desired level of precision can be estimated.…”

Estimating Occupancy of Rare Fishes using Visual Surveys, with a Comparison to Backpack Electrofishing

“…Snorkel sampling has an obvious advantage over electrofi shing because it greatly reduces handling stress and mortality, which is an important consideration when assessing the status of imperiled fi shes (Bohl et al 2009, Jordan et al 2008, Poos et al 2007). Our study indicated that the relative effectiveness of these two methods differed among species and that snorkel sampling was comparable or in some cases superior to electrofi shing for estimating site occupancy.…”

“…This problem was ignored in the past, but it is becoming increasingly more common to account for incomplete species detection in surveys for rare fi shes (e.g., Albanese et al 2007, Burdick et al 2008, Wenger et al 2008. Another challenge is the need to minimize handling stress and the risk of mortality for legally protected fi shes (Jordan et al 2008), which may restrict or preclude the use of effective but potentially harmful sampling methods such as electrofi shing (Bohl et al 2009). …”

Effects of Multiple Electrical Field Exposures on Cyprinid Embryo Survival

“…Previous research into the effects of electricity on fish embryo survival has been conducted by exposing embryos to electrical fields once and then monitoring survival (e.g., Cho et al 2002;Henry and Grizzle 2004;Bohl et al 2009;Bohl et al 2010 electrofishing (e.g., Bohl et al 2009) and pores do not close immediately after the electrical field is removed, it is possible that multiple exposures to electrical fields could increase embryo mortality by sustaining pores over a longer period of time that can "leak" cytoplasmic contents into the environment (e.g., Cerda et al 2006). Conversely, increased mortality resulting from multiple exposures of embryos to low-voltage gradients could make efforts to control invasive fish species at early life history stages using electricity more feasible.…”