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National Park Service, personal communication). A fixed complex-pulse current was delivered by the CPS unit, a newer and potentially less harmful control unit (Fredenburg 1992; Sharber et al. 1994). The CPS pulse pattern has a duty cycle of about 12% and consists of 15 "packets" or "trains" per second of three 240-Hz, 2.6-ms pulses (each separated by approximately 1.6 ms). Each control unit for all currents was set at 200 V output. Typical output from a WP-15 during electrofishing on the Green and Colorado rivers, Utah, at conductivities of 300-600 pS/cm is 200-300 V and 5-7 A (T. Chart, Utah Division of Wildlife Resources, personal communication). A fiberglass tank, 305 cm long X 30 cm wide X 30 cm deep, filled with well water at 18.50C was the treatment chamber. Water in the tank was 24 cm deep and had a conductivity of 650 pS/cm which approximated mean conductivity in the Green River near razorback sucker spawning areas upstream of Jensen, Utah, during late April through May, the period when peak spawning of razorback sucker usually occurs (T. Modde, U.S. Fish and Wildlife Service, personal communication). Electrodes were two 30 X 30-cm pieces of sheet metal placed parallel 21-173 cm apart to cover the full cross-sectional area of the treatment chamber and prOVide homogeneous electric fields. Distance between the electrodes was adjusted to produce the desired peak-voltage gradient. Peak-voltage gradients, as measured with an oscilloscope, were 1.2, 5.0, or 10.0 V/cm for the 60-Hz current and 1.2 V/cm for the 30-Hz, 80-Hz, and CPS currents. Corresponding power densities (Koltz 1989) were calculated as 936 pW/cm3 (1.2 V/cm), 16,250 pW/cm3 (5.0 V/cm) , and 65,000 pW/cm3 (10.0 V/cm). Treatments at 5.0 and 10.0 V/cm with the commonly used 60-Hz current were included to evaluate response of embryos and larvae to increases in electric-field strength. Peak voltage in the water for all electric fields was measured at 208 V. Viable embryos at one of the three developmental stages and pre-swimup larvae were exposed to one of the six electric fields for 10 s, an exposure time used in other investigations on effects of electrofishing fields on fish embryos (Dwyer et al. 1993; Dwyer and Erdahl 1995). Each treatment and corresponding control was replicated three times. Each replicate consisted of 20 embryos or larvae and was randomly assigned to treatments or controls. For shocking, embryos or larvae in each replicate were placed in a separate 16-cm long X 12-cm wide X 13-cm deep nylon-mesh basket suspended midway between the electrodes. Controls were handled the same as treatments but without exposure to electric current. Observations were made on behavior of larvae before and during treatment. For continued incubation or rearing after treatment, eggs were kept in the nylon- mesh baskets and larvae were transferred to 1-L glass beakers containing aerated well water. Containers were randomly placed in flow-through troughs, each 300 cm long X 30 cm wide X 20 cm deep, receiving well water at 180C. Eggs were examined at least twice daily through end of hatching, and obviously dead eggs in each replicate were recorded and removed to reduce spread of fungus. Time of hatching (hours postfertilization) and number of hatched larvae were recorded for each group of eggs. Hatched larvae were euthanized with an overdose of tricaine methanesulfonate (MS-222), fixed and preserved in 3% phosphate-buffered formalin, and later examined for evidence of obvious external abnormalities. Larvae treated at pre-swimup were reared for 4 weeks after treatment, and each replicate received as food the same measured quantity of recently hatched nauplii of Artemia sp. twice daily. Nauplii not consumed within 2 h after each feeding were siphoned from the beakers. Immediately after treatment and at weekly intervals thereafter, a random sample of seven larvae from each replicate was anesthetized in a solution of 100 mg/L 7