Acute toxicity and behavioral responses of coho salmon (Oncorhynchus kisutch) and shiner perch (Cymatogaster aggregata) to chlorine in heated sea-water

The acute toxicity and behavioral response to chlorinated and heated sea-water was determined for coho salmon smolts and 1–3 month old shiner perch. LC₅₀'s were determined for 7.5, 15, 30 and 60 min exposure times; 13, 16 and 20°C (Δt = 0, 3, 7°C) temperatures and total residual oxidant (TRO) concentrations ranging from 0.077 to 1.035 mg l⁻¹. The mean 60 min LC₅₀ for shiner perch was significantly reduced (P ≤ 0.05) from 308 μg l⁻¹ TRO at 13°C to 230 μg l⁻¹ TRO at 20°C. The 60 min LC₅₀ for coho salmon decreased from 208 μg l⁻¹ TRO at 13°C to 130 μg l⁻¹ at 20°C. The LC₅₀'s for coho salmon in chlorinated sea-water averaged 55% of those for shiner perch. The relationship between TRO concentration, exposure time, and percent survival in chlorinated sea-water at 13°C is presented for both species.A significant (P ≤ 0.01) avoidance threshold for coho salmon occurred at 2 μg l⁻¹ TRO and was reinforced with increasing temperature. A significant (P ≤ 0.01) avoidance threshold for shiner perch occurred at 175 μg l⁻¹ TRO, while a significant preference (P ≤ 0.05 or 0.01) response at 16°C and 20°C occurred at 10, 25, 50 and 100 μg l⁻¹ TRO. The ecological implications of the toxicity tests and the behavioral responses are discussed.