Piaractus mesopotamicus juveniles (total length 12 AE 0.5 mm) were exposed to different concentrations of ammonia-N (un-ionized plus ionized ammonia as nitrogen), using the static renewal method at different temperature levels (15, 20 and 25°C) at pH 7. The 24, 48, 72, 96 h LC 50 values of ammonia-N in P. mesopotamicus juveniles were 5.32, 4.19, 3.79 and 2.85 mg L À1 at 15°C; 4.81, 3.97, 3.25 and 2.50 mg L À1 at 20°C; and 4.16, 3.79, 2.58 and 1.97 mg L À1 at 25°C respectively. The 24, 48, 72, 96 h LC 50 values of NH 3 -N (un-ionized ammonia as nitrogen) were 0.018, 0.014, 0.013, 0.009 mg L À1 at 15°C temperature; 0.023, 0.019, 0.016 and 0.012 mg L À1 at 20°C; 0.029, 0.026, 0.018 and 0.014 mg L À1 at 25°C. The temperature increase from 15 to 25°C caused an increase of ammonia-N susceptibility by 21.80%, 9.55%, 31.92% and 30.87%, after 24, 48, 72 and 96 h exposure respectively. Furthermore, we found that exposure of fish to ammonia-N caused an elevation in total haemoglobin and blood glucose with an increase of 2 mg L À1 concentration. Ammonia levels tolerated, especially in different temperatures levels, have important implications for the management of aquaculture.
