Influence of Electrofishing Pulse Shape on Spinal Injuries in Adult Rainbow Trout

Abstract Adult rainbow trout Salmo gairdneri captured by electrofishing were analyzed for spinal injury by X-ray photography and autopsies. The effects of three electrical pulse shapes were compared. Of 209 fish captured, 50% suffered spinal injuries involving an average of eight vertebrae that were dislocated, splintered, or both. One-quarter-sine wave pulses injured a significantly higher proportion of fish (67%) than either exponential pulses (44%) or square wave pulses (44%; P < 0.05). Quarter-sine waves also damaged significantly more vertebrae per fish (average, 9.5) than did exponential pulses (6.6); the average number damaged by square waves (8.2) did not differ significantly from either of the other means. Electrofishing could bias mark–recapture studies of large rainbow trout. Electrofishing in waters containing endangered or threatened species should be considered with great caution.