Enhanced uranium tolerance of an exposed population of the eastern mosquitofish (Gambusia holbrooki Girard 1859)

Abstract

Genetic differences between populations of mosquitofish from a uranium(U)-contaminated stream were identified by starch gel electrophoresis. Fish collected from the uncontaminated mainstream of Upper Three Runs Creek (South Carolina, USA) exhibited greater genetic variability than those collected from the contaminated Tims Branch. Lower genetic variation displayed in Tims Branch fish could reflect selection associated with toxicant stress, a genetic bottleneck due to low population numbers at the contaminated site, or random genetic drift. A toxicity assay was performed to determine if these genetically distinct mosquitofish also displayed enhanced U tolerance. Times to death were compared for fish from an uncontaminated site and offspring of fish taken from the U-contaminated Tims Branch. After 7 days of exposure to 2.57 mg/L of U as uranyl nitrate, 98% and 96% of the naive population had died in the replicate tanks. In contrast, the final mortality for the offspring from the population previously exposed to U were 25% and 57% in the replicate tanks. Fish derived from the U-contaminated site were more tolerant than those from the uncontaminated site. Because these were second generation fish, this tolerance likely has a genetic basis.