Influence of Pulsed Direct Current Electrofishing on Mortality and Injuries among Four Centrarchid Species

The effects of pulsed direct current electrofishing on mortality of and injury to largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, bluegill Lepomis macrochirus, and pumpkinseed L. gibbosus were examined. The pulse frequencies were 30, 60, and 120 Hz, and conductivity categories of 122–214, 456–683, and 752–789 μS/cm were used. Three independent collections were made with nine different combinations of pulse frequency and range of conductivity. Fish were placed in holding pens for 72 h; dead fish were removed and autopsied immediately. Internal hemorrhages were documented by dissection; potential skeletal damage was determined by radiography. After 72 h, one-fourth of the caged fish were sacrificed and examined for internal hemorrhages. Of 454 largemouth bass collected, 6 died (1.3%) and another suffered external injury. Of 145 smallmouth bass, 1 died (0.7%) and another 5 (3.4%) exhibited external injuries. Of 568 bluegills, 30 died (5.3%). Fifty-five pumpkinseeds were examined and none died or were injured. Pulsed direct current electrofishing did not cause high mortality; none of the X-rayed fish exhibited skeletal damage. Mortality appeared to be caused by hemorrhages of the dorsal aorta and other nearby blood vessels in the caudal area.