Effects of Electroshock-induced Spinal Injury on Survival and Growth of Northern Pike

Abstract We undertook a study to evaluate the effect of electroshock-induced spinal injury on survival and growth of adult Northern Pike Esox lucius. Our study was conducted on 210 (140 treatment, 70 control) wild adult fish. We exposed treatment fish to 5 s of 120-Hz pulsed DC, then length-measured, x-rayed, double-marked, and released them into 0.04-ha ponds. X-ray images of all fish were evaluated for spinal injury. Of the 140 shocked fish, 28% were injured. After 37 days (9 May – 15 June 1991), the ponds were drained, and 193 surviving fish collected for estimates of short-term survival. Most of these fish (154) were deemed healthy and relocated to a 25-ha lake. After 290 days (15 June 1991 – 1 April 1992), we used gill nets to obtain recaptures for estimates of growth and long-term survival. For both shocked and control fish, short-term survival was in the low 90-percent range and long-term survival was in the low 40-percent range with no difference in survival between shocked and control fish. After 290 d, growth of shocked and control fish was not different. Long-term survival was significantly length dependent: Of the 154 fish released, 42% survived and were significantly larger at initial measurement than that of the 58% that did not. Despite electroshock and injury having no apparent effect on survival and growth, it is essential that injury be minimized. Based on our results, we advise against using 120-Hz pulsed DC electrofishing Northern Pike. Based on results in other studies, we recommend using 60-Hz pulsed DC.