Effects of Ammonia on Growth and Survival of Recently Hatched Channel Catfish

The lethal concentration for 1% of the test organisms (LCl) of un-ionized ammonia for 1-d-posthatch larval channel catfish Ictalurus punctatus in 96-h static-renewal exposures was 0.263 mg/L (95% confidence interval, 0.072–0.373 mg/L). The 96-h LC1 of un-ionized ammonia was 0.147 mg/L (95% confidence interval, 0.025–0.252 mg/L) for 7-d-old, newly transformed juveniles. Dry weights of fish that survived 7-d exposures were inversely related to un-ionized ammonia concentrations. The highest concentration of un-ionized ammonia tested that did not result in significant differences (P ≥ 0.05) in growth-the no-observable-effect concentration (NOEC)-for l-d-old larval and 7-d-old juvenile channel catfish was 0.082 and 0.093 mg/L, respectively. The lowest concentration of un-ionized ammonia tested that resulted in significant differences (P ≤ 0.05) in growth-the lowest-observable-effect concentration (LOEC)-for 1-d-old larval and 7-d-old juvenile channel catfish was 0.233 and 0.212 mg/L, respectively. The subchronic value, which is the geometric mean of the NOEC and LOEC, was 0.138 mg/L for 1 -d-old larvae and 0.141 mg/L for 7-d-old juveniles. This study demonstrated that short-term static-renewal toxicity tests using young channel catfish can detect growth inhibition resulting from exposure to a toxicant. No age-related changes were found for the sensitivity of channel catfish to un-ionized ammonia.