Metabolic responses to salinity acclimation in juvenile shortnose sturgeon Acipenser brevirostrum

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 degreesC for 10 weeks at salinities of 0parts per thousand, 5parts per thousand, 10parts per thousand and 20parts per thousand. 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 0parts per thousand and 20parts per thousand. In addition, tissue proximate analysis was performed on the white muscle of fish cultured at 0parts per thousand and 20parts per thousand. An initial change in plasma osmolality was observed in those fish cultured at the higher salinities (10parts per thousand and 20parts per thousand), 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 20parts per thousand 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 20parts per thousand 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 20parts per thousand, indicating a decreased aerobic capacity of the gill. (C) 2003 Elsevier Science B.V. All rights reserved.