Influence of Temperature Selection upon the Chlorine Avoidance of Cold-Water and Warmwater Fishes

Abstract

The avoidance response of selected cold-water (stenothermal) and warmwater (eurythermal) fish species to total residual chlorine (TRC) was found to be species specific, influenced by temperature, and dependent upon the constituents within the TRC. The first significant avoidance of TRC (primarily free chlorine) at 12 and 18 °C occurred at concentrations ranging from 0.05 to 0.10 mg/L for salmonids — rainbow trout (Salmo gairdneri), and coho salmon (Oncorhynchus kisutch) — and 0.10 to 0.40 mg/L at 12 and 24 °C for the eurythermal species — largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus), and mosquitofish (Gambusia affinis). A greater concentration of TRC was necessary to initiate avoidance at the highest acclimation temperature for most fish species tested although the amount of hypochlorous acid (HOCl) within the TRC was approximately the same regardless of the acclimation temperature at each avoidance concentration. For exposures comprised mainly of monochloramine (MONOCl), initial avoidance concentrations were generally equal to or greater than concentrations avoided in the TRC trials. After attraction into heated water, bluegill and largemouth bass avoided some TRC or MONOCl concentrations which were either equal to or twofold greater than the concentrations determined in tests without temperature attraction; for mosquitofish, the differences were as much as three to four times greater. Temperature attraction into chlorinated water was less influential for salmonids in elevating the avoidance response of chlorine with only a twofold increase in the avoidance concentration of TRC and none for MONOCl.Key words: chlorine avoidance, chlorine toxicity, temperature selection, stenothermal fish, eurythermal fish