Gas-bubble disease in three fish species inhabiting the heated discharge of a steam-electric station using hypolimnetic cooling water

Abstract

White bass (Morone chrysops), bluegill (Lepomis macrochirus), and largemouth bass (Micropterus salmoides) inhabiting the heated discharge canal of Duke Power Company's Marshall Steam Station, Lake Norman, North Carolina, were examined for signs of gas-bubble disease (GBD) during the winters of 1982–1983 and 1983–1984. Peak percentages of these fish species with GBD occurred between late February and early May each year, corresponding with peaks in total gas saturation in the discharge water. Cooling and warming water temperatures, and thermal stratification of Lake Norman influenced saturation of dissolved gases in the hypolimnetic intake water of Marshall Steam Station, and directly affected the variability in total gas saturation in the discharge canal. Temperature change in the condenser cooling water and electricity output were unrelated to the within-year variability in total gas saturation and GBD. The use of hypolimnetic water for cooling at this station restricts the time to a few months that levels of total gas saturation are sufficient to induce GBD, but probably led to higher peaks in GBD than if epilimnetic water was used. Among years, levels of GBD in white bass, bluegill, and largemouth bass were higher when electrical demand and mean temperature changes of the condenser cooling water at Marshall Steam Station were higher. Higher incidences in GBD in these fishes also occurred during winters when intake water temperatures were coldest.