No abstract

In the laboratory, we assessed the effects of electroshocking embryos and early larvae of razorback sucker Xyrauchen texanus with square-wave pulsed DC in homogeneous fields. Embryos at early epiboly, early tail bud. or fin fold developmental stages and pre-swim-up larvae were exposed for 10 s to simple pulse currents of 30 Hz (12% duty cycle). 60 Hz (24% duty cycle), or 80 Hz (40% duty cycle), or to a fixed complex pulse current of three 240-Hz, 2.6-ms pulses delivered at 15 Hz (12% duty cycle). Peak-voltage gradient for each current was 1.2 V/cm (power density = 936 jiW/cm 3 ). Tests were also conducted with the 60-Hz current at peak-voltage gradients of 5.0 V/cm (16,250 jiW/cm 3 ) and 10.0 V/cm (65.000 jiW/cm 3 ). Survival of embryos from treatment through hatching improved significantly (P ^ 0.05) at successive developmental stages; embryos at early epiboly were most sensitive to electric shock. Mean survival of embryos

We conducted laboratory experiments to address concerns about potential harmful effects of electrofishing on juvenile humpback chubs Gila cypha. Four types of square‐wave pulsed DC in homogeneous fields were tested: 30 Hz (12% duty cycle), 60 Hz (24% duty cycle), 80 Hz (40% duty cycle), and a complex pulse train of three 240‐Hz, 2.6‐ms pulses delivered at 15 Hz (12% duty cycle). We first determined peak‐voltage gradients for each current sufficient to induce the electroshock responses of taxis, narcosis, or tetany in captive‐reared early juvenile humpback chubs (49–96 mm total length) and bonytails G. elegans (46–79 mm). Bonytails were intended as surrogates for humpback chubs in most subsequent tests. However, mean voltage‐gradient response thresholds were 8–43% lower for humpback chubs than for bonytails. We then exposed 30 humpback chubs for 10 s to the complex pulse current at mean tetanizing field intensity and 60 bonytails for 10 s to one of the four currents at mean field intensities required for each of the three responses. All humpback chubs and half of the bonytails were euthanized, frozen, and later examined for internal injuries; remaining bonytails were reared for 98 d to assess effects on growth and survival. No mortalities, external injuries, or vertebral injuries were observed in either species. Moderately severe spinal hemorrhages were found in 20% of shocked humpback chubs and 13% of shocked bonytails. Shocked humpback chubs had a significantly higher (P ≤ 0.05) incidence of injuries than unshocked control fish. The number of injured bonytails was significantly higher (P ≤ 0.05) than controls in the 80‐Hz taxis treatment and the 30‐, 60‐, and 80‐Hz tetany treatments. Differences in the number of shocked bonytails with injuries among currents at each response threshold and among response thresholds for each current were not significant. No significant differences in injury rates were detected between humpback chubs and bonytails exposed to the complex pulse current at tetanizing field intensities. Growth of bonytails was not affected by shocking. Results suggest that electrofishing could cause spinal hemorrhages in some early juvenile humpback chubs but does not affect short‐term growth or survival. Studies are needed to evaluate the significance of electrofishing injuries in humpback chubs at the population level.

In the laboratory, we assessed direct effects of electroshock by two types of square‐wave pulsed DC in homogeneous fields of 1.0 peak volts per centimeter on ripe razorback suckers Xyrauchen texanus and evaluated subsequent egg‐hatching success. Four males and four females were exposed for 10 s to a simple 60‐Hz (24% duty cycle) current, and four males and three females were subjected for 10 s to a complex pulse pattern of three 240‐Hz, 2.6‐ms pulses delivered at 15 Hz (12% duty cycle). All shocked fish expelled some gametes during treatment. No external hemorrhages were observed, but X‐ray and necropsy examinations revealed injuries associated with the spinal column in two males and two females subjected to the 60‐Hz current and one female exposed to the complex pulse pattern; no injuries were observed in the four control fish (two males and two females). Mean percent egg hatch for fish shocked by either current was significantly lower (P ≤ 0.05) than that for control fish. Differences in hatching success between treatment currents were not significant. Electrofishing could adversely affect razorback sucker populations by injuring adults and reducing their reproductive success.