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Near simultaneous exposure to selenium and salinity stress is an environmental reality faced by white sturgeon juveniles in the San Francisco Bay-Delta, having the potential for adverse synergistic impacts on juveniles during seaward migration. White sturgeon juveniles (36-132 g) were transferred into higher salinities (15-20 ppth) after exposure to dietary selenium (0.4, 9.6, 20.5, 41.7, 89.8, or 191.1 lg Se/g diet) in the form of L-selenomethionine (SeMet) for 8 weeks in freshwater (0 ppth). White sturgeon fed above 41.7 lg Se/g diet experienced significant (P < 0.05) declines in survival relative to sturgeon fed between 0.4 and 41.7 lg Se/g diet when transferred into brackish water (15 ppth salinity) for 3 days. Plasma osmolality and ionic concentrations in white sturgeon after abrupt transfer correlated positively with dietary Se concentrations. Transfer of white sturgeon fed above 41.7 lg Se/g diet into 20 ppth brackish water for 1 day resulted in significant declines in survival relative to white sturgeon fed 0.4-41.7 lg Se/g diet. Hematocrit and dehydrational weight loss were significantly correlated with dietary Se concentrations while plasma osmolality and ion concentrations were not. The transfer of sturgeon into 20 ppth water for 3 days resulted in severe survival declines in all treatment groups. The results of this study suggest that the previously established threshold for Se toxicity (10-20 lg Se/g) is sufficient to protect white sturgeon from the adverse interactive affects resulting from increases in dietary Se and ambient water salinity.

The usefulness of a newly developed, combined technique consisting of esophageal intubation, dorsal aortic cannulation, and urinary catheterization to deliver Se orally and to monitor Se uptake, accumulation, and excretion in white sturgeon (Acipenser transmontanus) was explored. Groups of five yearling sturgeon (1-2 kg) each were intubated with 0 (sham), 250, 500, or 1,000 microg Se/kg body weight in the form of L-selenomethionine, an ecologically relevant organic form of Se. Selenium concentrations in whole blood, plasma, and red blood cells did not change in the sham group but began to rise within 2 h postintubation in the other groups, and levels remained near maximum concentrations throughout the 48-h sampling period. Average urinary Se excretion rates over the entire 48-h period were 0.05, 0.46, 0.61, and 2.15 microg Se/kg/h in sturgeon intubated with 0, 250, 500, and 1,000 microg Se/kg, respectively. Selenium excretion rates were highest within the first 6 h in all treatment groups except the sham group. Selenium concentrations in the liver were positively correlated with the intubated Se dosage.