Time of day and water temperature modify the physiological stress response in green sturgeon, Acipenser medirostris.

The effects of time of day and water temperature on the acute physiological stress response were investigated in young-of-the-year green sturgeon (Acipenser medirostris). The response to a 1-min air-emersion stressor was assessed during the day (08.00 h) and at night (20.00 h), as well as after acclimation to either 11 degrees C or 19 degrees C. Blood samples were collected prior to stress and at several times after exposure to the stressor, and plasma concentrations of cortisol, lactate, and glucose were determined. The magnitudes of cortisol (19.1 ng ml(-1) vs. 4.9 ng ml(-1)) and lactate (190.6 mg l(-1) vs. 166.7 mg l(-1)) were significantly higher in fish stressed at night when compared with the day. There were no significant differences in glucose levels between time periods. Although, acclimation temperature did not affect peak cortisol concentrations (56.7 and 50.3 ng ml(-1) at 11 degrees C and 19 degrees C, respectively), the duration of the response was significantly extended at 11 degrees C. Post-stressor lactate increases were similar between temperature groups, but at 11 degrees C post-stressor glucose levels were significantly increased through 6 h, suggesting stressor-induced glycogenolysis and gluconeogenesis or decreased glucose utilization. These data demonstrate that the physiological stress response in green sturgeon is modified by both time of day and temperature.