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expelled gametes during shocking; each female expelled at least several hundred eggs. No external hemorrhages were observed on any fish. X-ray and necropsy examinations revealed evidence of injuries associated with the spinal column in two males and two females (50% of fish) subjected to the 60-Hz current and one female (14% of fish) exposed to CPS. Each injured male had a class-3 hemorrhage dorsal to the spinal column and slightly anterior to origin of the dorsal fin. One female exposed to the 60-Hz pulse frequency had two vertebral injuries posterior to the dorsal fin: one rated as class 2 located slightly posterior to the anal fin and involving two vertebrae, and the other rated as a class-3 fracture located slightly posterior to the dorsal fin and involving three vertebrae. There was evidence of a class-1 hemorrhage dorsal to each vertebral injury. The other two females with injuries each had a c1ass-2 hemorrhage dorsal to the spinal column and slightly posterior to origin of the dorsal fin. No injuries associated with the spinal column were evident in control fish, and no damage to internal organs was observed in shocked or control fish. Some of the preserved unfertilized eggs from each treatment replicate and the control had ruptured chorions (8-12% of each 50-egg subsample). For all treatment replicates and the control, maximum diameter of unfertilized eggs averaged 1.8 mm (range, 1.5-2.0), and 2.1 mm (range, 1.8-2.3) for water-hardened eggs. Eggs in all lots began hatching at about 114 h post-fertilization, and hatching was completed about 10 h later. Hatching success in egg lots of treatment replicates exposed to either current was significantly lower than that in egg lots of the control. However, difference in mean egg hatching success between treatment currents was not significant. Egg hatch ranged 21.0-35.4% (mean, 25.9) for the control, 3.6-16.6% (mean, 10.6) for the 60-Hz treatment, and 2.0-10.2% (mean, 4.9) for the CPS treatment. Discussion Differences we observed in rate and severity of electroshock-induced injuries between the two currents are consistent with results of similar studies on other fishes by Fredenburg (1992) and Sharber et al. (1994). They demonstrated that CPS is less harmful to fish than simple DC pulse frequencies ~ 30 Hz. The only other published study on effects of pulsed DC on large-river fishes native to the Colorado River basin was by Cowdell and Valdez (1994). They found localized hemorrhaging along a portion of the spine in 5% of 40 adult roundtail chub Gila robusta (219-404 mm total length) collected from the upper Colorado River with a 8