Comparison of Laboratory and Field Avoidance Behavior of Fish in Heated Chlorinated Water

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Abstract
The effects of intermittent chlorination and temperature selection on the movement of fish were studied in an integrated field and laboratory project on the New River at the Glen Lyn Power Plant in southwestern Virginia. Over a temperature range of 7–36 C, the total number of fish sampled from the intermittently chlorinated thermal effluent was lower than control values (P ⩽ 0.09) when total residual chlorine (TRC) concentrations were ⩾ 0.15 mg/liter. After seasonal variations were segregated into discrete intervals of field temperature and fish avoidance of TRC, a decline in fish abundance in the chlorinated, heated discharge was observed within 95% confidence limits. In summer field temperatures of 27–30 C, fish avoided a TRC concentration that ranged from (95% confidence limits) 0.19 to 0.28 mg/liter TRC; when temperatures were falling from 26 to 7 C, they avoided 0.23–0.42 mg/liter TRC. The two most consistently sampled fish species, spotfin shiner Notropis spilopterus and whitetail shiner N. galacturus, generally avoided areas of the discharge when TRC concentrations were equal to 0.18 mg/liter in the temperature range of 24–29 C. At field temperatures of 30–34 C, however, whitetail shiners avoided 0.04 mg/liter TRC; spotfin shiner numbers did not decline until TRC concentrations were above 0.12 mg/liter. The lowest laboratory concentration avoided by spotfin shiners was 0.20 mg/liter TRC. The whitetail shiner was more sensitive in the laboratory at 12, 18, and 24 C (avoiding 0.11 mg/liter TRC) than at 30 C (0.20 mg/liter). Selection of test water heated to the preferred temperature of either species prior to chlorine addition did not alter subsequent avoidance of TRC concentrations except for spotfin shiners tested in combined residual chlorine (CRC) concentrations at 12 C (0.38 mg/liter CRC avoided). In most cases, laboratory‐determined avoidance concentrations predicted accurately the TRC concentrations that would elicit the avoidance behavior of fish under natural field conditions. Based on published acute toxicity tests with intermittent chlorination, spotfin shiners and most other fish species generally avoided chlorine residuals 50% or less of the median lethal concentrations.