Increased Toxicity of Ammonia to Rainbow Trout (Salmo gairdneri) Resulting from Reduced Concentrations of Dissolved Oxygen

Abstract
LC50 of aqueous ammonia at reduced dissolved O2 (DO) concentrations was tested in acute toxicity tests with rainbow trout (S. gairdneri) fingerlings using fifteen 96-h flow-through tests over the DO range 2.6-8.6 mg/l, the former concentration being the lowest at which control fish survived. There was a positive linear correlation between LC50 (mg/l unionized ammonia) and DO over the entire DO range tested; ammonia toxicity increased as DO decreased. Ammonia LC50 values were also computed for 12, 24, 48 and 72 h. The correlation with DO was greater with the shorter time period.