Serum osmolality and ion concentrations were measured in juvenile Chinese sturgeon Acipenser sinensis at different salinities to determine the isosmotic point. Isosmotic and isoionic concentrations were calculated from the regressions for serum and ambient osmolality, with Na(+) , Cl(-) and K(+) as salinities 9·19, 8·17, 7·89 and 9·70, respectively. These values were consistent with the salinity of the habitat where juvenile A. sinensis occur in the Yangtze Estuary, suggesting that an isosmotic salinity is an important factor driving their habitat choice.

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To understand salinity tolerance and osmoregulatory status of juvenile Chinese sturgeon, we transferred the hatchery-reared juveniles (mean 189.9 g, 8-months-old) directly from freshwater (0) to salinity 5, 10, 15, 20, and 25 for 192 h (8 days exposure), and measured the mortality, serum osmolality and ion concentrations of fish exposed to various salinities. No mortality occurred in sturgeon exposed to salinity between 5 and 20 during the course of the trial. Sturgeons exposed to salinity 25 began to die after 12 h, and did not survive 24 h. However, acute environmental salinities <20 should not pose a survival problem for this species. Both serum osmolality and ion concentration (Na + and Cl ) ) showed the same pattern in all salinity tests. In salinity 5, serum osmolaity and ion concentrations of juvenile Chinese sturgeon were not significantly different compared to freshwater exposed fish (P > 0.05). Serum osmolality and ion concentrations increased significantly (P < 0.05) in higher salinity treatments, reaching a peak at 12 h for fish in 10 and 15, and at 24 h for fish in 20 salinity. Thereafter, serum osmolality and ion concentrations decreased and reached a new steady state for fish in 10 and 15 salinity at the end of the trial, which was higher than for fish in freshwater. Serum parameters in fish exposed to salinity 20 decreased but remained unstable at 192 h, indicating a longer acclimation time was needed for fish exposed to higher salinities. The results indicate that 8-monthsold juvenile Chinese sturgeon must stay in the Yangtze River estuary for a period of time to acclimate and can not move directly towards the sea. This information will help to identify the appropriate salinity where cultured juveniles can possibly be restocked.

Summary To determine the teratogenic effects of lead (Pb) on young Chinese sturgeon (A. sinensis), fertilized eggs (96‐h) were exposed to Pb2+ until juvenile stages (total exposure 112 days). Three nominal concentrations were employed: 0.2 mg L−1, 0.8 mg L−1 and 1.6 mg L−1. After the exposure period, juveniles were returned to Pb‐free water for a subsequent 42 days depuration period. Fish exposed to 0.8 and 1.6 mg L−1 Pb2+ exhibited body deformities during the exposure phase, appearing mainly as curvatures to left or right at OD (Origin of dorsal fin) to OC (Origin of the dorsal caudal fin), and OC to PC (Posterior margin of caudal fin) as well as to the OP (Origin of pectoral fin), associated with ptosis at PC. Moreover, the higher the concentration of water‐borne Pb, the sooner body deformations occurred, while also affecting a larger proportion of the test individuals. Free locomotion and effective foraging was greatly reduced with increasing body deformation (lordosis). Pb accumulation in tissues was concentration dependent. Muscles accumulated relatively higher Pb which may have contributed to its effect on the muscle contraction potential and thus may have effected the neuromuscular system (muscle‐induced body curvature). Morphological recovery decreased during the depuration period and this was accompanied by declining tissue Pb concentrations, indicating some self‐repairing capacity.