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f?u-prerf lq qG North American Journal of Fisheries Management 16:473-476, 1996 © Copyright by the American Fisheries Society 1996 Effects of Two Electrofishing Currents on Captive Ripe Razorback Suckers and Subsequent Egg-Hatching Success ROBERT T. MUTH AND JACK B. RUPPERT Larval Fish Laboratory, Department of Fishery and Wildlife Biology Colorado State University, Fort Collins, Colorado 80523, USA Abstract.-In the laboratory, we assessed direct ef- fects of electroshock by two types of square-wave pulsed DC in homogeneous fields of 1.0 peak volts per centi- meter 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 pat- tern of three 240-Hz, 2.6-ms pulses delivered at 15 Hz (12% duty cycle). All shocked fish expelled some ga- metes 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 s 0.05) than that for control fish. Differences in hatching success be- tween treatment currents were not significant. Electro- fishing could adversely affect razorback sucker popu- lations by injuring adults and reducing their reproductive success. The razorback sucker Xyrauchen texanus is a federally designated endangered species endemic to the Colorado River basin (USFWS 1991). This fish was once widespread and common throughout the larger rivers of the basin, but only disjunct populations and scattered individuals exist today (Minckley et al. 1991). The largest extant riverine population of razorback suckers occurs in the mid- dle Green River system of northeastern Utah and northwestern Colorado, but the numbers of adults are low and recruitment is minimal (Tyus 1987; Lanigan and Tyus 1989; Modde et al. 1996). Electrofishing of spawning aggregations is an effective method for capturing adult razorback suckers in rivers (Tyus 1987; Tyus and Karp 1990), but concerns exist within the Recovery Imple- mentation Program for Endangered Fish Species in the Upper Colorado River Basin about potential harmful affects to spawning fish, their gametes, and early offspring. This study was part of the investigation to address those concerns and pro- vide information for establishing guidelines on the use of electrofishing to monitor endangered fishes in the Colorado River basin. Our objective was to 22L7) determine if electroshock by two types of pulsed DC affected captive ripe razorback suckers and subsequent egg-hatching success. Methods Ten ripe males and 10 females in near-ripe con- dition were allotted for this study from razorback sucker broodstock maintained at Dexter (New Mexico) National Fish Hatchery and Technology Center. Males were 499-551 mm total length (mean, 526 mm) and weighed 1.36-1.80 kg (mean, 1.63 kg). Females were 551-599 mm (mean, 575 mm) and weighed 1.93-2.61 kg (mean, 2.28 kg). Fish were transported to U.S. Fish and Wildlife Service facilities in Grand Junction, Colorado, for final maturation of eggs, electroshocking, and ar- tificial fertilization of eggs. Males and females were separated and held indoors in hauling tanks filled with aerated water at 17-20°C. The largest female was injured during removal from the hatch- ery raceway and died prior to treatment, about 16 h after transport. Ovulation was induced by intra- muscular injections of 220 units human chorionic gonadotropin per kilogram body weight at 24-h intervals (Hamman 1985) beginning on the day of transport. Six of the remaining nine females began ovulating after receiving two injections; the other three females began ovulating after receiving a third injection. Electroshocking of fish was begun when all females were ovulating. Electric systems were powered by a Honda® model EG5000X, 5000-W, 240-V generator. Al- ternating current from the generator was trans- formed to square-wave pulsed DC by a Coffelt® VVP-15 or Coffelt Mark 20 complex pulse system (CPS®) electrofishing control unit. Settings for the VVP-15 were 60 Hz and 24% duty cycle (4-ms pulses). These settings are commonly used with the VVP-15 in boat electrofishing for adult razor- back suckers in the middle Green River system (E. Wick, U.S. National Park Service, personal com- munication). The CPS unit, a newer and potentially less harmful control unit (Fredenburg 1992; Shar- ber et al. 1994), produces a fixed complex pulse pattern consisting of 15-Hz "packets" of three 473