AVOIDANCE RESPONSE OF THE COMMON SHINER TO CHLORINE 827 



suggest that the common shiner was less influenced by the presence of 

 chloramine and was more sensitive to a low threshold concentration of HOCl in 

 TRC treatments. 



Fish populations inhabiting thermally influenced waters near 

 power-plant installations often encounter chlorine perturbations 

 resulting from antifouling practices. Residual chlorine concentrations 

 for certain regions of a plant's discharge vary from 0.1 to 0.5 mg/liter 

 (Becker and Thatcher, 1973), with a recommended maximum 

 weekly average of free residual of 0.2 mg/liter (Environmental 

 Protection Agency, 1973). Although these chlorine levels are 

 potentially hazardous to most aquatic biota, including fish, species 

 that actively detect and avoid sublethal or lethal residuals may not 

 suffer deleterious effects. Field studies have demonstrated the ability 

 of fish to avoid polluted water (Katz and Gaufin, 1952; Sprague, 

 Elson, and Saunders, 1965; Tsai, 1968; 1970). Power-production 

 discharges are unique, however, in that many fish species Eire 

 attracted to the thermal plumes, which periodically contain toxic 

 chlorine residuals. 



Many earlier investigations dealing with chlorine toxicity (see 

 reviews by Brungs, 1973; 1976) did not adequately consider the 

 constituents comprising total residual chlorine (TRC). When rela- 

 tively high levels of nitrogenous compounds are present, most of the 

 chlorine residual may be in a combined (CRC) or chloramine form 

 (Clark, Viessmann, and Hammer, 1971). In relatively unpolluted 

 water the residual may be in an uncombined or free form (FRC), 

 which, depending on pH and temperature, is comprised of hypo- 

 chlorous acid (HOCl) and hypochlorite ion (OCl"~). Hypochlorous 

 acid is considered to be the most toxic of these components (Becker 

 and Thatcher, 1973), but each component differentially influences 

 fish physiology and avoidance behavior. Heath (1977) supported 

 the hypothesis that the toxic actions of CRC and FRC are based on 

 separate physiological mechanisms. In behavioral studies, Fava and 

 Tsai (1976) reported that the blacknose dace {Rhinichthys atratulus) 

 avoided FRC to a lesser degree than it did CRC. Micropterus 

 punctulatus and Notropis rubellus were shown to avoid very low 

 concentrations of HOCl (Cherry et al., 1977). In addition, avoidance 

 responses to chlorine have been snecies specific. Rainbow trout 

 {Salmo gairdneri) demonstrated a ve^y sensitive response to chlorine 

 concentrations of 0.001 mg/liter (Sprague and Drury, 1969), but 

 rockbass {Ambloplites rupestris) failed to significantly avoid doses 

 <0. 80 mg/liter TRC (Cherry et al., 1978). Threshold or first 

 avoidance responses of four other species were within a narrower 



