Ontogeny of the cortisol stress response in lake sturgeon Acipenser fulvescens as influenced by substrate and temperature during early development

Lake sturgeon eggs were hatched on gravel or slate or in hatchery jars in 2008 to determine the impact of substrate on the ontogeny of the hypothalamic-pituitary-interrenal stress axis. The experiment was repeated in 2009, along with the impact of temperature on the HPI axis. Larvae were unable to respond to a stressor via an increase in cortisol concentrations until the onset of exogenous feeding. Substrate studies indicate that larvae hatched on gravel or slate or in hatchery jars were capable of increasing cortisol levels when stressed. Resting concentrations of cortisol were higher in the slate treatment (17.59+/-3.49 ng.g -1) as compared to gravel (5.67+/-0.41 ng.g -1). When stressed, the magnitude of response was equivalent for substrates (73.05+/-8.11 ng.g-1 and 62.65+/-6.98 ng.g -1 for slate and gravel, respectively). The duration of response varied, with gravel-treatment larvae exhibiting an extended response. Results from temperature studies indicate that development and yolk sac absorption rates were most rapid at 15°C. Larvae reared at 9 and 15°C had elevated resting whole-body cortisol concentrations as compared to fish reared at ire (38.6+/-3.1 ng.ml-1 at 9°C, 5.67+/-0.41ng.ml -1 at 12°C, and 25.38+/-2.84ng.ml-1 at 15°C). When stressed, larvae reared at 9°C were incapable of increasing cortisol concentrations. Larvae reared at 12 and 15°C did not differ in the magnitude of response when stressed (62.65+/-6.98 ng.g-1 and 69.05+/-6.48 ng.g-1, respectively). As with the substrate experiments, the duration of responses did vary, with larvae reared in 12°C exhibiting an extended response. Complementary catecholamine data in response to a stressor indicate higher concentrations of norepinephrine as compared to epinephrine concentrations at rest. Rapid increase in norepinephrine and epinephrine occurred upon stressing, with a greater increase noted for epinephrine within 1 minute post-stress.