The Effects of Intermittent Chlorination on Rainbow Trout and Yellow Perch

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Abstract
[Intermittent chlorination of cooling waters for fouling control is a common practice in the electric power generating industry.] Rainbow trout, Salmo gairdneri, and yellow perch, Perca flavescens, were exposed to residual Cl for single 30-min and triple 5-min doses. Tests were conducted at 10, 15 and 20.degree. C with both species plus 25 and 30.degree. C for the perch. Single exposure 30-min LC50 values for the perch ranged from 0.70 mg/l at 30.degree. C to 8.0 mg/l at 10.degree. C. Triple 5-min exposure LC50 values for the perch were 22.6 and 9.0 mg/l at 10 and 20.degree. C, respectively. Rainbow trout 30-min LC50 values were 0.99 and 0.94 mg/l at 10 and 15.degree. C, respectivel. Two groups of trout tested at 20.degree. C yielded 30-min LC50 values of 0.60 and 0.43 mg/l. Triple exposure 5-min LC50 values for the trout were 2.87 mg/l at 10.degree. C and 1.65 mg/l at 20.degree. C. Mortality occurred immediately after exposure to Cl in the 30-min perch tests at 10 and 15.degree. C, but was delayed 2-12 h at the higher temperatures. This pattern was reversed in the 5-min triple exposure tests. Rainbow trout exhibited rapid mortality in all tests except the 10.degree. C triple exposure series where mortality was delayed 12-24 h. For both species, concentrations resulting in no mortality were approximately 1/2 the LC50 value.