ACCUMULATION OF AMMONIA IN THE HEMOLYMPH OF PENAEUS-MONODON EXPOSED TO AMBIENT AMMONIA

Individual Penaeus monodon (13.02 +/- 0.65 cm, 12.90 +/- 0.81 g) were placed in 10, 50 or 100 mg/l ammonia-N (un-ionized plus ionized ammonia as nitrogen) in 34 ppt seawater at pH 8.2; and in 50 mg/l ammonia-N at pH 6.3, 7.2, 8.2 and 9.0, respectively. Background haemolymph ammonia values were 12.33 +/- 2.18 mg/l and 7.11 +/- 0.20 mg/l ammonia-N, respectively, for shrimp feeding normally and shrimp starved for 2 days. No significant difference (P > 0.05) in haemolymph ammonia was observed between the controls and shrimp exposed to 10 mg/l for 1 h. However, haemolymph ammonia of shrimp exposed to 10, 50 and 100 mg/l was significantly (P < 0.05) higher than the controls after 1.5 h exposure. After only 15 min, haemolymph ammonia of shrimp exposed to 50 mg/l at pH 9.0 was significantly higher (P < 0.05) than those exposed to 50 mg/l at pH of 6.3, 7.2 and 8.2. Shrimp exposed to 50 mg/l at pH 9.0 and 100 mg/l at pH 8.2 accumulated maximal concentrations of ammonia in 1.5 h and 6 h, respectively. Both NH3 (un-ionized ammonia) and NH4+ (ionized ammonia) affected ammonia accumulation and caused death of shrimp. Once shrimp had accumulated up to 20 mg/l ammonia-N in the haemolymph, they were weakened and eventually died. Thus, concentrations of haemolymph ammonia can be used as an index of ammonia loading for P. monodon in intensive culture systems.