Electrofishing the littoral zone of Lucchetti Reservoir, Puerto Rico, from 1992 through 1997 indicated dynamic changes in fish community structure, despite consistent annual water level regimes. Nine species of fish, including 2 cichlids, 2 centrarchids, and 2 ictalurids, were collected. Relative abundance varied significantly over seasons and years for most species. One species, the bigmouth sleeper (Gobiomorus dormitor), may have become extirpated during the period and 1 new species, armored catfish (Liposarcus multiradiatus), became established. Adult largemouth bass (Micropterus salmoides) varied nearly 3-fold in density and 1.5-fold in biomass over 5 years, as estimated by mark-recapture. Despite annual variability in community structure and prey base composition, relative weights of adult largemouth bass were consistently close to 100. Although more variable than typical southeastern reservoirs, Lucchetti Reservoir is capable of supporting a productive largemouth bass fishery.