Effects of ontogeny, season, and temperature on the swimming performance of juvenile green sturgeon (<i>Acipenser medirostris</i>)

Abstract

Because some salmonids show decreased swimming performance (U crit ) during their parr-smolt transformation, we tested the hypothesis that juvenile anadromous green sturgeon (Acipenser medirostris) decrease U crit during their analogous ontogenetic stage. Juvenile green sturgeon (mean age: 98 days) that had not reached seawater tolerance had a positive relationship of U crit (cm·s –1 ) with total length (TL), whereas seawater-tolerant sturgeon (mean age: 150 days) had a negative relationship of U crit with TL. This U crit decrease was presumably seasonal because a similar-sized group of fish tested later (mean age: 288 days) showed a linear increase in U crit with TL. Smaller sturgeon displayed both morphological (larger relative pectoral fin surface areas) and behavioral (rostrum wedging and pectoral fin holding) attributes for station holding in a riverine environment. In a second experiment to test the effects of increased river temperature near the predicted time of downstream migration, U crit and heat-shock protein concentrations increased at 24 °C compared with at 19 °C (mean age: 155 days). Thus, although there was evidence for cellular stress, the swimming ability of the fish was not compromised. Therefore, water velocity, temperature, and time of year should be considered in life-stage-specific efforts to manage or protect green sturgeon.