Metabolic responses to salinity acclimation in juvenile shortnose sturgeon Acipenser brevirostrum

Abstract

The influence of salinity on the metabolic processes was investigated in the shortnose sturgeon Acipenser brevirostrum . Hatchery-reared juveniles (mean 274 g, 16 months old) were cultured at 18 °C for 10 weeks at salinities of 0‰, 5‰, 10‰ and 20‰. Plasma ions and metabolites were measured to assess the osmoregulatory and metabolic status of the fish through the experimental period. At the conclusion of the trial, metabolic enzymes were measured in several tissues, as were gill and intestinal Na + K + -ATPase in fish cultured at 0‰ and 20‰. In addition, tissue proximate analysis was performed on the white muscle of fish cultured at 0‰ and 20‰. An initial change in plasma osmolality was observed in those fish cultured at the higher salinities (10‰ and 20‰), followed by a return to values observed in fresh water acclimated fish. No significant changes were observed in total plasma free amino acid (FAA) concentrations. Changes were observed in individual amino acid concentrations, some of which may be related to an increased demand for oxidizable substrates in fish exposed to seawater. Total non-esterified fatty acid (NEFA) concentrations were elevated initially in the fish cultured at 20‰ compared with those cultured in fresh water (1732.1±288.1 and 1060.5±119.7 nmol/ml). The proximate analysis revealed a lower white muscle lipid level in fish cultured at 20‰ compared to fish cultured in fresh water (1.1±0.1% and 2.1±0.5%). This suggests that lipids are important in meeting the energetic demands of salinity exposure. An oxidative enzyme (cytochrome- c oxidase) was lower in the gills of fish cultured at 20‰, indicating a decreased aerobic capacity of the gill.