We evaluated the effects of a single electroshock on injury and mortality of hatcheryreared Cape Fear shiners Notropis mekistocholas (N ϭ 517), an endangered cyprinid. Groups of 18-22 Cape Fear shiners were exposed to DC, 120-Hz pulsed DC (PDC), or 60-Hz PDC at voltage gradients of 1.1, 1.9, or 2.7 V/cm for 3 s. Mortality occurred only among fish exposed to 120-Hz PDC (25%) and DC (38%) applied at 2.7 V/cm. Because no mortality occurred in Cape Fear shiners exposed to 60-Hz PDC, this waveform was selected for further study of electroshock duration (3, 6, 12, 24, or 48 s) and voltage gradient (0.9, 1.6, or 2.3 V/cm). Most fish electroshocked in the experiments were immobilized (ceased swimming motion). No physical injury was detected by necropsy or radiography in any fish. Electroshock-induced mortality of Cape Fear shiners showed a strong multivariable relationship to voltage gradient, electroshock duration, and fish length. Fish subjected to 60-Hz PDC at 0.9 or 1.6 V/cm for 6 s experienced low mortality (Ͻ10%). Our results demonstrate that Cape Fear shiners can be immobilized by 60-Hz PDC electroshock without injury or significant risk of mortality. We propose that electrofishing may be safely used to sample similar small cyprinids, imperiled or otherwise, when electrofishers select an appropriate waveform (DC pulsed at 60-Hz or less) and use it judiciously (minimal exposure at, or below, the immobilization threshold).

We compared the incidence of internal injuries in adult American eels Anguilla rostrata captured by trap‐netting (N = 20) and by 30‐Hz, pulsed‐DC electrofishing (N = 18) in the St. Lawrence River, New York. On average, the lengths and weights of fish caught by the two methods were similar. Radiographic imaging revealed that spinal damage occurred in 60% of the electroshocked American eels but only 15% of the trap‐netted American eels. Bilateral filleting showed hemorrhages in 30% of the electroshocked fish but none of the trap‐netted fish. Electrofishing caused significantly higher incidences of both spinal damage and hemorrhage than did trap‐netting. Most electroshocked American eels had multiple spinal injuries; hemorrhages occurred only in fish with multiple sites of vertebral damage. We recommend that workers avoid the use of 30‐Hz, pulsed DC to capture American eels that are intended for release; a lower frequency, such as 15 Hz, may significantly reduce injury but may also result in unacceptably low capture rates. We hypothesize that electroshocked American eels are at high risk for injury because of their large size (>90 cm) and high vertebral count (>100).

Most sturgeon (Acipenseridae) populations are threatened or depleted. Assessment operations that could harm individuals in these populations, such as electrofishing, must be evaluated. The risk of electrofishing-induced injury in juvenile white sturgeon Acipenser transmontanus associated with electrical waveform (60-Hz pulsed DC [PDC] versus DC) and fish size (small [24-33 cm], age 1 versus large [37-54 cm] age 2) was evaluated in a tank experiment. Exposure to a homogeneous electric field of 1.2 V/cm immobilized all white sturgeons exposed to electrical treatments. No injury was found in the control groups. The risk for hemorrhage was significantly greater among white sturgeons exposed to PDC than among those exposed to DC (relative risk ϭ 6.7; 95% CI ϭ 3-29). Both size-groups were at significantly more risk for hemorrhage when exposed to PDC than to DC. All white sturgeons exposed to DC recovered (upright orientation and normal swimming) in less than 30 s; 95% recovered immediately. Most large sturgeons exposed to PDC required 1-2 min for recovery; most small sturgeons recovered immediately. Our results suggest that if electrofishing is conducted in waters where imperiled populations of white sturgeons are present, DC should be considered for use instead of 60-Hz PDC. If 60-Hz PDC must be used, electrofishers should be aware that a substantial portion of fish immobilized (complete cessation of movement) while electrofishing will probably be injured (hemorrhages). Results from other studies indicate that the incidence and severity of injury from PDC electrofishing can be reduced by using lower voltages and pulse frequencies (e.g., 60 Hz to 20-30 Hz) while maintaining capture responses less severe than immobilization (e.g., galvanotaxis).

The aim of this study was to determine the suitability of water quality in the Roanoke River of North Carolina for supporting shortnose sturgeon Acipenser brevirostrum, an endangered species in the United States. Fathead minnows Pimephales promelas were also evaluated alongside the sturgeon as a comparative species to measure potential differences in fish survival, growth, contaminant accumulation, and histopathology in a 28-day in situ toxicity test. Captively propagated juvenile shortnose sturgeon (total length 49 ± 8 mm, mean ± SD) and fathead minnows (total length 39 ± 3 mm, mean ± SD) were used in the test and their outcomes were compared to simultaneous measurements of water quality (temperature, dissolved oxygen, pH, conductivity, total ammonia nitrogen, hardness, alkalinity, turbidity) and contaminant chemistry (metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, current use pesticides, polychlorinated biphenyls) in river water and sediment. In the in situ test, there were three non-riverine control sites and eight riverine test sites with three replicate cages (25 · 15-cm (OD) clear plexiglass with 200-lm tear-resistant Nitex Ò screen over each end) of 20 shortnose sturgeon per cage at each site. There was a single cage of fathead minnows also deployed at each site alongside the sturgeon cages. Survival of caged shortnose sturgeon among the riverine sites averaged 9% (range 1.7-25%) on day 22 of the 28-day study, whereas sturgeon survival at the non-riverine control sites averaged 64% (range 33-98%). In contrast to sturgeon, only one riverine deployed fathead minnow died (average 99.4% survival) over the 28-day test period and none of the control fathead minnows died. Although chemical analyses revealed the presence of retene (7-isopropyl-1-methylphenanthrene), a pulp and paper mill derived compound with known dioxin-like toxicity to early life stages of fish, in significant quantities in the water (251-603 ng L )1 ) and sediment (up to 5000 ng g )1 dry weight) at several river sites, no correlation was detected of adverse water quality conditions or measured contaminant concentrations to the poor survival of sturgeon among riverine test sites. Histopathology analysis determined that the mortality of the river deployed shortnose sturgeon was likely due to liver and kidney lesions from an unknown agent(s). Given the poor survival of shortnose sturgeon (9%) and high survival of fathead minnows (99.4%) at the riverine test sites, our study indicates that conditions in the Roanoke River are incongruous with the needs of juvenile shortnose sturgeon and that fathead minnows, commonly used standard toxicity test organisms, do not adequately predict the sensitivity of shortnose sturgeon. Therefore, additional research is needed to help identify specific limiting factors and management actions for the enhancement and recovery of this imperiled fish species.

Electric current is routinely applied in freshwater for scientific sampling of fish populations (i.e., electrofishing). Freshwater mussels (families Margaritiferidae and Unionidae) are distributed worldwide, but their recent declines in diversity and abundance constitute an imperilment of global significance. Freshwater mussels are not targeted for capture by electrofishing, and any exposure to electric current is unintentional. The effects of electric shock are not fully understood for mussels but could disrupt vital physiological processes and represent an additional threat to their survival. In a controlled laboratory environment, we examined the consequences of exposure to two typical electrofishing currents, 60-Hz pulsed DC and 60-Hz AC, for the survival of adult and early life stages of three unionid species; we included fish as a quality control measure. The outcomes suggest that electrical exposure associated with typical electrofishing poses little direct risk to freshwater mussels. That is, adult mussel survival and righting behaviors (indicators of sublethal stress) were not adversely affected by electrical exposure. Glochidia (larvae that attach to and become parasites on fish gills or fins) showed minimal immediate reduction in viability after exposure. Metamorphosis from glochidia to free-living juvenile mussels was not impaired after electric current simulated capture-prone behaviors (stunning) in infested host fish. In addition, the short-term survival of juvenile mussels was not adversely influenced by exposure to electric current. Any minimal risk to imperiled mussels must be weighed at the population level against the benefits gained by using the gear for scientific sampling of fish in the same waters. However, scientists sampling fish by electrofishing should be aware of mussel reproductive periods and processes in order to minimize the harmful effects to host fish, especially in areas where mussel conservation is a concern.