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

Penaeus japonicus (14.12 +/- 0.74 cm, 13.91 +/- 0.65 g) were exposed individually in 34 ppt seawater to 5, 10, 50 and 100 mg l-1 ammonia-N (un-ionized plus ionized ammonia as nitrogen) at pH 8.2: additional trials were run using 100 mg l-1 ammonia-N at pH 6.3, 7.2, 8.2 and 9.0. Background hemolymph ammonia values were 4.45 +/- 0.44 mg l-1 and 3.00 +/- 0.32 mg l-1 ammonia-N, respectively, for shrimp feeding normally and shrimp starved for 2 d. Shrimp exposed to 5, 10, 50 mg l-1 and controls survived 16 h trial exposures. No significant difference (p > 0.05) in hemolymph ammonia was observed between controls and shrimp exposed to 5 mg l-1 for 16 h. However, hemolymph ammonia of shrimp exposed to 10, 50 and 100 mg l-1 was significantly higher (p < 0.05) after 2 h exposure than for controls. Hemolymph ammonia of shrimp exposed to 100 mg l-1 ammonia-N at pH 9.0 was significantly higher (p < 0.05) than of those exposed to the same concentration at pH 6.3, 7.2 and 8.2. Shrimp exposed to 100 mg l-1 ammonia-N at pH 9.0 and 8.2 accumulated maximal concentrations of ammonia in 30 min and 12 h, respectively. Those exposed to 50 mg l-1 ammonia-N at pH 8.2 reached a maximum after 16 h. Both NH3 (un-ionized ammonia) and NH4+ affected ammonia accumulation and caused death; shrimp which had accumulated ammonia-N in the hemolymph to a level of 20 mg l-1 were weakened and eventually died.