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;' ~~. ~,'.: , Figure 8. Dark stripes through and behind dorsal fin of arctic grayling are burn scars created from touching "live" electrodes when electrofishing (Photo courtesy of Larry Kolz). Delayed Effects of Electrofi__^_shin~ As stated earlier, the strength of the field, and duration or exposure time that_a-fish. remains in an electrical field, determines whether the fiah will live or die. Death. can occur immediately after shocking, and in these instances is usually caused by respiratory failure, hemorrhaging, or fractured vertebrate. Death can also occur days or weeks later, and in these instances, is most likely the result of the combined effects of stress, ex- haustion, or physical damage. In one early report, delayed morta lity was called "lingering death" (Anonymous 1441). This incident occurred at a federal hatchery in Cortland, New York, Lightning struck a tree 150 feet from rearing ponds containing brown (SaZmo trutta) and brook trout. Apparently the electrical charge traveled through the ground to the ponds where it stunned fish. Fish were observed having difficulty maintaining their equilibrium in the water. Some of the fish recovered in a short time, but others "died suddenly" a week later. Those fish that suffered delayed mortality showed the internal symptoms of hemorrhaging and the external symptoms of fractured vertebrae (S-shaped). Other examples of delayed mortality are described by DeMont (1971) and Novotny (pers. comm.). DeMont observed mortality in threespine stickleback- (~Gasterosteus acuZeatus) five days after shocking (Figure 9), although most mortality occurred in the first 24 hours, He used both ac and do currents in his experiment, and observed about a 12~ difference in mortality between the two, with ac being the most injurious. In a combined electrofishing, tag and mark operation in Wisconsin (D, Novotny, Wisc. Dept. of Nat. Res. pers. comm.), 25~ mortalities were observed in largemouth bass (1~lieroptemcs salmoides) and walleyes (stizostedion vitreum) two weeks after shocking. Most of the mortalities occurred after CAL-NEYA WILDLIFE TRANSACTIONS 1984 68