"Swimming Improves High Temperature Tolerance of Striped Bass"

In ectothermic fish, temperature affects all biochemical, physiological and life history activities. Thus defining thermal range is important for ecosystem-based management and predicting effects of climate change. The standard method for measuring fish thermal tolerance is the critical thermal maxima test (CT_Max), wherein fish are exposed to gradually increasing temperatures until they lose equilibrium. We tested CT_Max in striped bass Morone saxatilis under moderate-flow and traditional static-flow conditions to assess if swimming affects thermal tolerance.  For an active pelagic fish such as M.saxatilis, assessing their thermal tolerance under flow conditions may be more environmentally realistic. Each of 12 fish underwent a CT_Max test while swimming and resting. Fish were acclimated to the test chamber for at least 24 hours before a test and had at least one week of recovery between tests.  Contrary to expectations, the average CT_Max for fish swimming at 50% of their estimated critical swimming speed was significantly higher (P<0.05; repeated measures ANCOVA -length as covariate) than for the same fish under static flow (34.77° C versus 34.23°C). These results suggest that loss of equilibrium at high temperature is an entirely neural phenomenon and that different blood flow distributions during swimming cause the brain to warm slower.