The object of these electrofishing investigations was to develop lightweight portable equipment for collecting fish in almost inaccessible high mountain streams.

Electrofishing, which involves a very dynamic and complex mix of physics, physiology, and behavior; has been a valuable sampling technique for over half a century, but its potentially harmful effects on fish must be recognized, monitored, and avoided or minimized, especially with respect to populations of endangered species. Spinal injuries and associated hemorrhages, although often not externally obvious or fatal, can occur anywhere in the electrofishing field at or above the intensity threshold for twitch. These injuries are believed to result from powerful convulsions 0 body musculature caused mostly by sudden changes in voltage. Significantly fewer spinal injuries are reported when direct current, low-frequency pulsed direct current (#30 Hz), or specially designed pulse trains are used. Salmoninae are especially susceptible. Endangered cyprinids of the Colorado River Basin are generally much less susceptible, but the endangered catostomid Xyrauchen Texanus appears sufficiently susceptible to warrant minimal-use policy. Other harmful effects, including bleeding at gills or vent and excessive physiological stress, are also of concern. Mortality, usually by asphyxiation, is a common result of excessive exposure to tetanizing intensities near electrodes or poor handling of captured specimens. Reported effects on reproduction are contradictory, but electrofishing over spawning grounds can harm embryos.