Summary

Description

The lower Gunnison River and the Colorado River are designated critical habitat for two endangered fish species: the Colorado pikeminnow Ptychocheilus lucius and the razorback sucker Xyrauchen texanus. Approximately 95 river miles of these river segments are state listed as impaired because selenium concentrations exceed the chronic standard for the protection of aquatic life. There is continual need to monitor fish tissue selenium concentrations to assess remediation effectiveness in conjunction with remediation efforts undertaken by the local selenium task force. Muscle plug biopsies provide a nonlethal sampling method to determine selenium residues in endangered fish. There is a need for accurate and validated conversion factors to predict selenium in whole body fish, as well as ovarian with eggs concentrations from measured muscle plug residues for comparison to established toxicity thresholds. Selenium concentrations in ovaries and eggs provide the most reliable endpoint to assess risk of reproductive impairment from selenium toxicity. We have developed tissue selenium prediction equations using two fish species; the green sunfish Lepomis cyanellus and the white sucker Catastomus commersoni. These prediction equations were tested on other fish species to measure performance. Whole body selenium concentrations predicted from muscle plug concentrations were usually within 30 of the actual measured values. Ovaryegg selenium concentrations predicted from muscle plug concentrations were usually underestimated; especially for black bullhead Ictalurus melas, channel catfish Ictalurus punctatus, brown trout Salmo trutta, and roundtail chub Gila robusta. Fish varied by species when partitioning different selenium loads into their ovaryegg tissues. Black bullheads, channel catfish, and brown trout partition more selenium into ovarieseggs compared to other species. Green sunfish and white suckers exhibited seasonal differences in ovaryegg selenium concentrations, with prespawning females carrying significantly higher selenium loads than postbreeding females. Selenium concentrations in endangered Colorado River fish were at levels known to impair reproduction in other fish species.