Acute ammonia toxicity and the interactive effects of ammonia and salinity on the standard metabolism of European sea bass (Dicentrarchus labrax)

Ammonia tolerance of European sea bass (Dicentrarchus labrax) juveniles (1.1 +/- 0.3 g) was investigated by a series of acute toxicity experiments at different salinity levels (10, 20 and 30 ppt) at pH 8.0 and temperature 22 degrees C. Oxygen consumption rates were also measured to determine the Standard Metabolism (SM) of the fish. The tolerance of the fish to total ammonia nitrogen (TAN) and unionized ammonia (NH3) increased significantly with increasing salinity levels. The safe level for European sea bass was estimated to be 0.4, 1.0 and 1.6 mg L-1 for TAN and 0.02, 0.04 and 0.07 mg L-1 for NH3 at 10, 20 and 30 ppt salinity levels, respectively. At any, each level, the SM of the fish increased with increasing TAN concentration (P < .01). The SM of the fish at 10, 20 and 30 ppt gradients is 284, 282 and 272 mg h(-1) kg(-1), respectively at 0 mg L-1 TAN concentration (P < .01). This study indicates that European sea bass, a euryhaline teleost fish, has a low tolerance to ammonia at any salinity level.