Ozonation has been successfully applied in experimental fish culture recirculation systems, especially to oxidize some of the most important metabolites (such as nitrite, ammonium, BOD) at times when these concentrations reach a daily peak level. In this study the oxidation rates for ammonium, nitrite, and BOD have been determined for each of these components separately or in combination, using an improved design of the contacting chamber. Two flow rates and three ozone concentrations were employed. Ammonia oxidation rates were slowest while nitrite and BOD removal was rapid. Ozone concentrations substantially influenced the oxidation rates for ammonium ion. Nitrate was oxidized equally rapidly under almost all operational conditions. Slight differences in oxidation rates were noted for both ammonia and nitrite as long as the BOD was high.