834 CHERRY et al. 



0.20 mg/liter) for the rosyface shiner (Notropis rubellus) and spotted 

 bass (Micropterus punctulatus), and Cherry et al. (1978) reported the 

 same trends for smallmouth bass, (Micropterus dolomieui) and the 

 Coho salmon (Oncorhynchus kisutch). 



A greater concentration of chloramine (0.205 mg/liter), in 

 comparison with TRC levels comprised of CRC and FRC, was 

 required to initiate the threshold avoidance behavior of the common 

 shiner at 12 and 24°C (Table 2). In TRC concentrations at 12°C, 

 avoidance first occurred when the CRC level was 0.087 mg/liter, with 

 a FRC fraction of 0.122 mg/liter. At 24°C, CRC and FRC levels 

 comprising the TRC were nearly equal. The presence of FRC at 

 certain minimal concentrations may initiate avoidance behavior 

 sooner since the CRC fraction in the TRC trials was approximately 

 half the amount of the chloramine avoidance threshold. 



Excess ammonia concentrations were minimal (0.006 to 

 0.013 mg/liter) at the chloramine avoidance thresholds in both 

 unheated and heated trials and did not significantly influence 

 avoidance behavior (Table 2). At higher ammonia nitrogen concen- 

 trations (0.069 to 0.207 mg/liter in heated trials), fish resided in the 

 ammonia-treated water more often than in the untreated river water 

 (Fig. 1). Similar trends were reported by Jones (1948). 



Comparing avoidance thresholds for chloramine vs. TRC trials 

 indicated that higher chloramine than FRC concentrations were 

 required to produce an avoidance response (Table 2). For example, 

 at 12°C, the common shiner showed a stronger preference for the 

 warmer water (17.6°C) than at the 24°C trial (preference of 26.8°C). 

 A chloramine concentration at least twice as high as the amount 

 needed in the other chloramine or TRC trials (0.399 mg/liter) was 

 necessary to force the shiner from the preferred water. Although the 

 FRC avoidance thresholds in preferred temperature trials were less 

 than those in unheated conditions, the HOCl components of both 

 were generally the same. Therefore, a specific minimal HOCl fraction 

 may influence threshold avoidance behavior more than the CRC 

 components regardless of temperature. Fava and Tsai (1976) 

 reported, however, that chloramine concentrations were more 

 instrumental in avoidance behavior than free residual chlorine for 

 blacknose dace, but HOCl was not considered. Differences in 

 experimental designs and the fact that domestic wastewater was used 

 could account for these ambiguities. 



In our studies much of the variability in threshold avoidances to 

 TRC and its components was reduced when responses were evaluated 

 as a function of the HOCl fraction. Cherry et al. (1977) reported that 

 the most consistent patterns of chlorine avoidance by the spotted 



