Lethal effects of ammonia and nitrite on Penaeus penicillatus juveniles at two salinity levels

Abstract

1. The 24,48,96, 144-hr lc50 (median lethal concentration) of ammonia on Penaeus penicillatus juveniles were 59.49, 38.72, 29.77, 25.03 mg/l and 50.28, 31.26, 24.88, 20.66 mg/l for ammonia-N (un-ionized plus ionized ammonia as nitrogen); and 2.22, 1.44, 1.11, 0.93 mg/l and 2.00, 1.25, 0.99, 0.82 mg/l for NH3-N (un-ionized ammonia as nitrogen) in 34 and 25 ppt seawater, respectively. 2. The 24, 48, 96, 144-hr lc50 of nitrite-N on P. penicillatus juveniles were 92.88, 79.45, 40.86, 26.29 mg/l and 83.34, 52.93, 38.52, 25.55 mg/l in 34 and 25 ppt seawater, respectively. 3. A decrease of salinity from 34 to 25 ppt increased by more than 20% toxicities of ammonia and nitrite to P. penicillatus juveniles. 4. The “threshold” was found at 156 and 144 hr for ammonia, and 192 and 168 hr for nitrite in 34 and 25 ppt, respectively. 5. The “safety level” for P. penicillatus juveniles was 2.37 and 1.97 mg/l for ammonia-N; 0.09 and 0.08 mg/l for NH3-N and 2.04 and 2.28 mg/l for nitrite-N in 34 and 25 ppt, respectively.