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,~a THE PHYSIQLOrICAL EFFECTS OF ELE~TROFISHING Lee Emery) Fisheries Academy U. S. Fish and Wildlife Service National Fisheries Center-Leetown Box 700 Kearneysville, WV 25430 ABSTRACT. 5, Electrofishing is a valuable tool frequently used-to assess and manage fish populations. Techniques and equipment for electrofishing have been perfected over the years, but there are drawbacks that some users fail to recognize. One of these drawbacks, physiological stress, can damage or kill a fish weeks. after initial contact with the electrical current. This paper .summarizes effects produced 6y using ac, dc, and pulsed do systems. Specific examples are described. Severity of the shock, which is determined by strength of the field and total exposure time, can be controlled by the user to minimize physiological impacts. Suggestions are made to help reduce physiological stress caused 6y electrofishing. _ INTRODUCTION Biologists-have been electrofishing for many years. It is customarily assumed that most shocked fish recover shortly after capture and release. However, that is not always the case. This paper examines some physiological stresses caused by electrofishing and supplies the biologist with examples of how to prevent injuring fish. It is hoped that this paper acts as a refresher to the user so that electrofishing can continue to be the nonconsumptive sampling tool it was designed to be. DISCUSSION Electrofishing is a technique whereby electrical energy is put into the water and fish, intercepting this energy, are drawn toward the probes and incapacitated in such a way that they can be captured with nets. The movement of fish toward. the source of electricity is called galvanotaxis and is believed to be a result of direct stimulation of the central and autonomic nervous systems which control the fish's voluntary and involuntary .reactions. The involuntary contraction of the fish`s muscles causes a forced swimming toward the probe. These are all complex physiological responses which won't be discussed in great detail, how- ever, I will give a general synopsis of these interactions. When a fish intercepts an electrical current in water, electrical stimuli are transmitted via sensory nerve fibers to modulators (brain and spinal cord) and via motor nerve fibers to affectors (.glands and muscles). Neurons within nerve fibers carry impulses by a "wave of electrical depolarization" that moves along nerve fibers producing an electrical potential or polarization that is dependent upon the semipermeable membrane of the neurons. Stimuli must reach a minimum strength or threshold intensity quickly and last long enough to cause impulses to be transmitted. If this does not happen, and stimuli are of low intensity and short duration, impulses will not be transmitted. However, there are instances when present address: U. S. Fish and Wildlife Service, Division of Program Operations-- Fisheries, 18 and C Sts. NW., Washington, D. C. 20240. CAL-NEVA WILDLIFE TRANSACTIONS 1984 59