28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Electroshocking-Induced Injuries In Newly Transformed Juvenile Fish Theodore B. Henry and John M. Grizzle Southeastern Cooperative Fish Disease Project, Department of Fisheries and Allied Aquacultures, Auburn University, Auburn, Alabama 36849, USA Electroshocking-induced in fish have not been described histologically, and little is known about these injuries in fish that have recently completed the transformation from larva to juvenile.  We electroshocked newly transformed juvenile channel catfish Ictalurus punctatus, rainbow trout Oncorhynchus mykiss, striped bass Morone saxatilis, largemouth bass Micropterus salmoides, bluegill Lepomis macrochirus, and Nile tilapia Oreochromis niloticus.  Fish were exposed for 5 s (bluegill only) or 20 s to homogeneous electric fields of 30- to 120-Hz pulsed DC.  Only 2.8% of the survivors (N = 800) and 0.7% of fish that died immediately after electroshocking (N = 600) had gross injuries.  Hemorrhage in the posterior trunk or anterior tail was the most common gross lesion, occurring in 17 fish.  Nine of these fish were examined histologically, and 8 had an injured vertebra, sometimes associated with a notochord hernia, at the location of hemorrhage.  In largemouth bass, bluegill, and channel catfish that survived electroshocking without gross injury, a vertebral injury occurred in 17% (N = 12) of bluegill exposed for 5 s (8 V/cm) and in 40% (N = 15) of channel catfish (4 V/cm).  No vertebral injury occurred in 16 bluegill exposed for 20 s (4 V/cm) or in 22 largemouth bass (2 V/cm).  Necrotic skeletal muscle was the most common histological lesion, occurring in 60% of channel catfish, 64% of bluegill, and 18% of largemouth bass that survived electroshocking without gross injury.  Necrotic muscle was also found in one control largemouth bass (8%) and one control bluegill (20%).  The types and frequencies of histological lesions were similar in fish that survived or died after electroshocking. Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page