Effect of Electrofishing Pulse Shape and Electrofishing-Induced Spinal Injury on Long-Term Growth and Survival of Wild Rainbow Trout

Abstract
High rates of spinal injury from electrofishing have been reported for rainbow trout Oncorhynchus mykiss, but little is known about the fate and performance of injured fish. We conducted a long-term experiment to evaluate how incidence and severity of electrofishing-induced spinal injury affects growth and survival. We electroshocked 866 wild rainbow trout from the Gallatin River, Montana, using one of three different DC pulse shapes (smooth, half pulse, and full pulse), X-rayed the fish to determine degree of spinal injury, and compared short-term (100-d) growth and long-term (335-d) growth and survival after transplanting the fish to a 0.6-ha pond (stocking biomass, 255 kg/ha). Rainbow trout shocked with pulsed DC had significantly higher (P = 0.0001) incidence (40–54%) of spinal injury than those shocked with smooth DC (12%); injuries were also more severe among fish captured with pulsed DC (P < 0.01). Incidence and severity of injury were positively correlated with fish length (r = 0.79–0.83, P < 0.02). Few surviving fish (7 of 418) at the end of the study exhibited outwardly visible spinal deformities. Healing of spinal injuries was readily apparent on radiographs as evidenced by calcification and fusion of damaged vertebrae. Long-term survival of rainbow trout was not affected by pulse shape used during capture or by severity of electrofishing-induced injury. However, fish with moderate to severe injury (spinal misalignment and fracture), representing 28% of the total number shocked, had markedly lower growth and condition after 335 d than fish with no or low spinal injury.

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