Establishment and impact of redbelly tilapia in a vegetated cooling reservoir

Abstract

Redbelly tilapia (Tilapia zilli Gervais) rapidly established a reproducing population in a North Carolina power plant cooling reservoir after inadvertent introduction in 1984. It eliminated the submersed macrophyte community, including a 57-ha infestation of Egeria densa (Planch.) by late 1985. In August 1985, just prior to macrophyte disappearance from the reservoir, the mean estimates of redbelly tilapia density and standing crop were 1,080 fish/ha and 16.6 kg/ha, respectively. When macrophytes were scarce or absent, redbelly tilapia shifted to a diet dominated by detritus. The ability of redbelly tilapia to switch to alternate food sources permitted its population to continue expanding in the absence of macrophytes, the preferred food. Changes in water quality were minimal after macrophyte removal with no increased nutrient enrichment. Factors leading to the establishment of redbelly tilapia were an overwintering refuge provided by continuous thermal discharge > 10 C from the power plant, a paucity of predators largemouth bass (Micropterus salmoides Lacepede) and bluegill (Lepomis macrochirus Rafinesque), and the species ability to utilize alternate food sources following macrophyte removal.