Comparative Mortality of Three Esocids due to Stocking Stressors

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Abstract
For stocked sportfish, stocking stress can cause substantial mortality. We evaluated mortality of three young-of-year esocids, northern pike (Esox lucius), muskellunge (E. masquinongy), and their F1 hybrid, the tiger muskellunge, in response to simulated handling, transport, and thermal stressors in the laboratory. In 15.degree. C acclimated esocids, a 10.degree. rapid temperature increase caused little mortality. A 12.degree. increase killed some fish in all taxa; however, mean mortality did not differ significantly among northern pike (.hivin.X = 30%), tiger muskellunge (.hivin.X = 23%), and muskellunge (.ovrhdot.X = 10%). Nearly all 15.degree. C acclimated fish (98%) died in response to a 15.degree. increase. Tempering (0.15.degree..cntdot.min-1) did not reduce this near complete mortality. Handling (30 s dipnet) and transport confinement (60 g.cntdot.L-1 for 120 min) also did not alter mortality when compared with a 12.degree. temperature increase alone. Field experiments, completed concurrently, confirmed our laboratory finding that healthy esocids, acclimated to 15.degree. C, stocked at lake temperatures corresponding to a temperature increase .ltoreq. 10.degree., suffered little mortality. Because mortality did not differ among these two species and their hybrid, differential vulnerability to these stocking stressors need not be considered when deciding which esocid to stock.