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Table 5. Incidence of injured vertebrae in electroshocked bluegills exposed to different voltages and currents (Adapted from Spencer 1967) during exposure times ranging from 1-120 seconds, Equipment Average percentage injured AC 230 V, 3.1 amp 12.2 AC 115 V, 2.0 amp 4.6 DC 115 V, 1.9 amp 1.5 These two examples point out the serious differences between ac and do currents and their effects on fish. Pulsed do is the f`~/orite among most biologists today because of its ability to produce a good electrotactic response, minimize injuries, and is generally less costly to operate than other battery powered do systems. All this is not to say, however, that ac should not, or cannot, be used. One should be particularly careful whenever using ac systems and recognize its dangers and drawbacks. Ac systems appear to be most suitable in situations where the water conductivities are very low (e.g „ soft waters with less than 50 mg/1 total alkalinity). Suggestions for Field Application 1. Electrofishing works because fish are drawn involuntarily toward an anode or are in- capacitated in such a way that they can be easily collected. 2. It is important to target the species pursued as size, species, physiological state, and habitat all influence electrofishing success. 3. Electrofishing stresses a fish. Fish can suffer extreme physiological changes as a result of electrofishing and it is important that the collector be aware of these stress potentials whenever using electrofishing equipment. 4. It is important that one monitor fish collected by electrofishing and observe their recovery to insure that power settings are not lethal. It is also important to remember that it is the total electrical energy absorbed by the fish that deter~rines whether that fish will live or die. 5. Delayed mortality has been observed in fish collected by electrofishing. Most mortality occurs within the first 24 hours. Fish that show external signs of injury as a result of capture are most likely to show delayed mortality. Burn marks on fish are indi- cators of excessive electrical power. 6. Pulsed do produces the least physiological damage to fish .compared with those collected with do or ac electrofishing equipment. ACKNOWLEDGMENTS Much of the information contained herein was taken from the unpublished "Print%ples and Techniques of Electrofishing" manual used for teaching the Electrofishing Course given by the Fisheries Academy. Much of the material contained in that manual was-written or col- lected by Dr. R~~chard S. Wydoski, and I want to thank him for allowing me to use portions of that material for this presentation. I would also like to thank Larry Kolz, of the Denver Wildlife Research Center, for use of his arctic grayling photograph, and Carolyn Banks and Monte Stuckey for preparing the graphics. CAL-NEVA WILDLIFE TRANSACTIONS 19$4 70