Effects of thermal effluent on body condition of largemouth bass

Abstract

PAR POND, an 1,100-hectare reservoir in South Carolina, has received heated effluent from a nuclear production reactor since 1957. A notable feature of the reservoir¹ is the abundance and abnormally high catchability of largemouth bass (Micropterus salmoides²). Most reported responses of bass to the thermal situation in Par Pond are interpreted as inconsequential^3–7; increases in the densities of certain intestinal parasites⁸ and the incidence of red-sore disease⁹ in thermal areas are considered detrimental. Fishery scientists use body condition¹⁰ as an index for estimating a fish's well-being or fitness¹¹ as well as the relative suitability of the habitat¹². Body condition (K) of an individual is established by the relationship K = 10⁵ W × L⁻³, where W = body weight (g) and L = standard length (mm). However, caution must be exercised to ensure that ontogenetic changes in body shape, seasonal and sex differences, and small sample sizes do not preclude the effective use of the index for comparative purposes among individuals¹⁰. This report takes these reservations into account and compares body condition of largemouth bass collected from heated and unheated waters in Par Pond. The unique feature of this study is that data from 10 years are available on a large sample (n > 10,000) of largemouth bass, an important species of warm water sport fish. Lower body condition is associated with moderate thermal conditions comparable to many industrial settings and is correlated with lower levels of stored fat and with the incidence of red-sore disease.