Eco-Physiology of Juvenile Snook Centropomus Undecimalis (Bloch): Life-History Implications

Hypoxia is an environmental factor that affects a myriad of behavioral, physiological and habitat-use aspects of the life-history of fish. Snook, Centropomus undecimalis (Bloch), exhibit marked ontogenetic differences in habitat-use that we propose are based on physiological constraints and environmental conditions that change as the fish grow. To test this hypothesis, we compared known life-history data with laboratory tests of hematocrit, osmotic and chloride ion regulation, weight-dependent oxygen consumption and ventilation rates, and mortality. These data were also compared to field tests of size-dependent mortality under normoxic and hypoxic conditions. Under hypoxic conditions snook showed significant increases in hematocrit and decreases in plasma chloride ion concentration. Snook also exhibited significantly reduced metabolic rates, concomitant increases in ventilation rates, and increased mortality in hypoxic conditions. These ontogenetic physiological differences correlate with juvenile snook migration from impounded mangrove swamp habitat at sizes between 100–150 mm SL (about 45.0 g WW) along Florida's east-central coast.