Chronic toxicity of ammonia to juvenile gilthead seabream Sparus aurata and related histopathological effects

Effect of 20 days exposure of juvenile gilthead seabream (Sparus aurata) to elevated levels of ammonia on growth and survival was examined in a continuous flow system. Suppressed growth and reduced survival were observed at concentrations of 8.2 and 13 mg l⁻¹ total ammonia‐N (0.5 and 0.7 mg l⁻¹ un‐ionized ammonia‐N, respectively) and higher. The maximum acceptable toxic concentration (MATC) for growth was between 4.8 to 8.2 mg l⁻¹ total ammonia‐N (0.3 and 0.5 mg l⁻¹ un‐ionized ammonia‐N, respectively). Fish exposed to high ammonia levels (13 mg l⁻¹ total ammonia‐N, 0.7 mg l⁻¹ un‐ionized ammonia‐N) displayed clear signs of liver pathology. Existing evidence suggests that S. aurata is less sensitive to ammonia than other reported marine and freshwater fish. Under certain conditions ammonia concentration in the intensive fish ponds in Eilat may exceed the no observed effect concentration for S. aurata.