The influence of salinity on growth and metabolism was investigated in the shortnose sturgeon, 'Acipenser brevirostrum'. Juveniles were cultured for 10 weeks at 0, 5, 10 and 20 salinity. An initial perturbation of plasma ion and metabolite levels was observed followed by a return to values observed in fresh water acclimated fish. Nonetheless, it is unlikely that salinity acclimation is fully attained in these fish as a reduced growth performance was measured in fish exposed to seawater. Growth performance was greatest in fish reared at 0, while fish reared at 20 exhibited the poorest growth. The biochemical changes suggest that lipids are important in meeting the energetic demands of salinity exposure, as muscle lipid was lower and plasma nonesterified fatty acids higher in fish cultured at 20. Additionally, seawater exposed fish displayed an increased glycolytic potential and a depressed oxidative capacity indicating suboptimal salinity acclimation. An estimation of the energetic costs of osmoregulation is presented.