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<br />Executive Summary <br /> <br />In the laboratory, we assesed effects of electroshock by square-wave pulsed DC in <br />homogeneous fields on embryos and early larvae of razorback sucker Xyrauchen texanus. <br />Embryos at early epiboly, early tailbud, or finfold developmental stages and pre-swimup <br />larvae were exposed for 10 s to simple-pulse currents of 30 Hz (12% duty cycle), 60 Hz <br />(24% duty cycle), or 80 Hz (40% duty cycle), or a fixed complex-pulse current (CPSTM) of <br />three 240-Hz, 2.6-ms pulses delivered at 15 Hz (12% duty cycle). Peak-voltage gradient for <br />each current was 1.2 Vlcm (power density = 936 pW/cm3). Tests were also conducted with <br />the 60-Hz current at peak-voltage gradients of 5.0 (16,250 pW/cm3) or 10.0 V/cm (65,000 <br />pW/cm3). Survival of embryos after treatment through hatching improved significantly <br />(P s 0.05) with advancing developmental state; embryos at early epiboly were most <br />sensitive to electric shock. Mean survival of embryos at each developmental stage was <br />significantly greater (P s 0.05) in controls than in all treatments except those with 30 Hz or <br />CPS at early tailbud and finfold. Within the 60-Hz treatments at each developmental stage, <br />survival of embryos decreased with increasing peak-voltage gradient. Survival of larvae <br />through 4 weeks after treatment was not affected by exposure to electric current, but mean <br />growth of control larvae was significantly greater (P s 0.05) than that of larvae in all <br />treatments. Mean growth of larvae was not significantly different among treatments. <br />Results suggest that electrofishing over active razorback sucker spawning areas could <br />significantly harm developing embryos and early larvae. <br /> <br />Keywords.-Razorback sucker, Xyrauchen texanus, electrofishing, embryos, larvae. <br /> <br />5 <br />