Summary

Description

Endangered pallid sturgeon and congeneric shovelnose sturgeon found in the lower Platte River, NE and elsewhere in the Missouri River basin have elevated tissue levels of selenium. Their piscivorousomnivorous diet and long period of recrudescence between spawns facilitates Se bioaccumulation into eggs and hence offspring exposure. Earlylife stages of fishes embryolarva are sensitive to Se effects and are thought to be a significant bottleneck limiting sturgeon populations. Therefore, the objective of this study was to determine what concentrations of Se affect survival of young Scaphirhynchus sturgeon. Embryos were injected with graded doses of selenoLmethionine SeLMet nominal doses: 0, 6, 10, 18, 32 g Seg dry egg wt within 24h postfertilization PF to simulate maternal exposure to selenium. Developmental effects were evaluated at 7d PF. Mortality was assessed at 17d PF and mortality and growth were evaluated at 32d PF. Genotoxic effect of Se was evaluated at 32d PF by erythrocyte micronuclei. Actual mean Se concentrations in embryos immediately after injection were estimated to be 9, 12, 17, 23 g Seg egg and 6, 7, 13, 17 g Seg egg for shovelnose and pallid, respectively. Background egg concentrations were 5 gg egg and 3 gg egg for shovelnose sturgeon and pallid sturgeon, respectively. Developmental deformities delayed development, edema, and skeletal deformities were mostly observed within the first 7d PF at a nominal dose 10 g Seg egg. A higher percentage of pallid larvae than shovelnose larvae presented with developmental deformities and these were lethal. In general, mortalities were highest within the first 17d PF. Shovelnose mortality was significant at estimated doses of 17 and 23 gg egg. Pallid sturgeon mortality was significant at the highest estimated dose tested of 17 g Seg egg. However, overall pallid survival was low for all doses and time points and fertilization rate for pallid eggs was lower than for shovelnose eggs, suggesting that poor pallid sturgeon egg quality may have confounded results. Growth was not significantly affected in either species. Although the magnitude of the effects differed between the species, the effective selenium concentrations and the associated types of deformities were similar. The results of these studies will assist biologists in determining whether selenium toxicity is a factor limiting recovery of the pallid sturgeon in some parts of its range.