Fathead minnows (Pimephales promelas) were exposed to mercury (1.69, 6.79, and 13. 57 µg/l HgCl2; 10 d exposure) and afterwards tested using various metrics of foraging ability while feeding in a vegetated habitat. Among the foraging metrics were foraging efficiency, capture speed, and the ability to learn and retain information regarding habitat characteristics. Comparisons with control fish and fish from the two highest exposure groups revealed consistent performance deficits in foraging efficiency and capture speed. However, no treatment effects on learning were detected. In determining the underlying proximate cause of the foraging deficits, it is believed that the greater pause time exhibited by treatment fish while foraging was the main cause of treatment differences. In the future, behavioral studies will continue to allow toxicity testing of environmentally relevant variables such as those used by behavioral ecologists. Such tests, when combined with tests of field collected specimens, could prove powerful in linking laboratory toxicity to toxicity in wild populations. / Master of Science