Thermal Effluent and the Epizootiology of the Ciliate Epistylis and the Bacterium Aeromonas in Association with Centrarchid Fish

Abstract

Epistylis sp. (Ciliophora: Peritricha) is a facultative ectosymbiont of fresh-water fishes in streams and lakes throughout the southeastern USA. In combination with the Gram-negative bacteria A. hydrophilia, epizootic outbreaks of Epistylis have been implicated in the death of many thousands of game fish, primarily striped bass and several species of Centrarchidae (sunfish), in several reservoirs in North Carolina. While these epizootics have been correlated with high levels of organic loading, recent studies suggest that thermal loading from a nuclear production facility may influence the level of infection by A. hydrophilia and Epistylis sp. (A-E complex) on centrarchid sunfish in Par Pond Savannah River Plant, Aiken, S.C. Utilizing electro-fishing techniques, 11,500 sunfish from 6 spp. were collected and examined for external lesions associated with the A-E complex. Striped bass [Roccus saxatilis], and largemouth bass (Micropterus salmoides) were most heavily infected, followed in incidence of infection by bluegill (Lepomis macrochirus), warmouth (L. gulosus) and redbreast sunfish (L. auritus); lesions were not observed on the surface of black crappie (Pomoxis nigromaculatus). The body conditions (or K-factor) of more than 2000 largemouth bass were calculated; direct correlations were found between thermal loading, body condition and incidence of infection. Data are discussed in terms of thermal effluent and the epizootiology of Epistylis sp. and A. hydrophila.