Physiological Responses of Lake Erie Freshwater Drum to Capture by Commercial Shore Seine

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Abstract
Physiological changes associated with pronounced capture stress in freshwater drum (Aplodinotus grunniens) were studied. Increasing the exposure of exercised freshwater drums to low‐oxygen water resulted in increasing degrees of skin reddening and partial hemolysis in blood samples. Artifacts associated with blood sampling by heart puncture did not cause hemolysis, nor did a loss of Na+ and Cl− ions or an influx of water into the blood. Blood from freshwater drums that were severely distressed by seine capture showed no significant changes in hematocrit and plasma Na+ and Cl− concentrations, compared to fish that were exercised to near exhaustion by capture but were only briefly exposed to low oxygen. After 40 minutes of forced exercise in a low‐oxygen aquarium freshwater drums lost equilibrium and had extensive skin reddening, symptoms also observed in freshwater drums that were captured in a commercial shore seine. Blood from cannulated freshwater drums that were exhausted in the laboratory showed significant (P < 0.01) increases in plasma glucose and lactic acid, but no significant (P > 0.01) change in hematocrit or hemoglobin, compared to nonexercised freshwater drums. The apparent in vivo hemolysis was observed in blood from laboratory and field groups of exhausted freshwater drums, whereas all of the control fish blood samples displayed no more than slight evidence of hemolysis. Free hemoglobin probably contributes to skin reddening in freshwater drums and other fish, and both symptoms are likely results of a blood acid‐base imbalance in seine‐captured freshwater drums.