Note
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.