Physiological responses of largemouth bass to acute temperature and oxygen stressors

P>Temperature and oxygen gradients exist in nearly every water body, but anthropogenic activities can subject fish to rapid changes in these important environmental variables. These rapid changes in temperature and oxygen (generally referred to as temperature or oxygen shock) may have sub-lethal consequences depending upon the magnitude and the fish species. This study quantified physiological changes in largemouth bass, Micropterus salmoides (Lacepede), exposed to two levels of heat and cold shocks and to two levels of hypoxic and hyperoxic shocks. Following a cold shock from 20 degrees C to 8 degrees C, plasma cortisol and glucose increased after 1 h and lactate dehydrogenase activity increased after 6 h. Plasma glucose and K+ concentrations increased 1 h after a heat shock from 20 degrees C to 32 degrees C but not after 6 h. Bass subjected to a hypoxic shock from 8 to 2 mg O-2 L-1 showed decreased plasma K+ and increased plasma glucose and white muscle lactate. No changes in physiological parameters were observed in bass subjected up to 18 mg O-2 L-1 hyperoxia. Results from this study suggest that largemouth bass can tolerate a wide range of temperature and oxygen shocks, but temperature decreases of 20 to 8 degrees C and hypoxia as low as 4 mg O-2 L-1 should be avoided to minimise physiological perturbations.