Physiological and molecular responses of juvenile shortnose sturgeon (Acipenser brevirostrum) to thermal stress.

The shortnose sturgeon (Acipenser brevirostrum LeSueur, 1818) is a vulnerable species that is found along the eastern coast of North America. Little is known about temperature tolerance in this species and with a rapidly changing global climate, it becomes increasingly important to define the thermal tolerance of this species to better predict population distribution. Using a modified critical thermal maximum test (CTMax), the objectives of this study were to determine the impact of heating rate (0.1, 0.2 and 0.25°Cmin-1 ) on the thermal tolerance, associated hematological responses, and oxygen consumption in juvenile sturgeon. In addition, transcripts associated with physiological stress and heat shock (i.e., heat shock proteins) were also measured. Heating rate did not alter the CTMax values of shortnose sturgeon. Neither heating rate nor thermal stress affected plasma sodium and chloride levels, nor the expression of transcripts that included catalase, glucocorticoid receptor, heat shock protein70 (hsp70), heat shock protein 90α (hsp90α) and cytochrome P450 1a (cyp1a). However, regardless of heating rate, thermal stress increased both plasma potassium and lactate concentrations. Glucose levels were increased at heating rates of 0.2 and 0.25°Cmin-1 , but not at 0.1°Cmin-1 . Overall, oxygen consumption rates increased with thermal stress, but the response patterns were not affected by heating rate. These data support the hypothesis that shortnose sturgeon can tolerate acute heat stress, as many physiological and molecular parameters measured here were non-responsive to the thermal stress.