Toxicity of Ammonia and Nitrite to Penueus monodon Juveniles

Pcnaeus monodon juveniles (35.4 ± 2.2 mm TL) were exposed to seawater (20 ppt) having different concentrations of total ammonia (NH₃+ NH,+) and nitrite. Median lethal concentration (LC₅₀) was determined with static-renewal tests. The LC₅₀, of total ammonia-N, NH₃-N and niMte-N on shrimps decreased with increase of exposure time. The 24, 48, 72, % and 120 h LC₅₀ were 94.96, 61.09, 47.47 45.58 and 38.00 mg/L total ammonia-N (2.68, 1.73, 135, 1.29 and 1.08 mg/L NH₃-N) and 215.85, 185.33, 88.54, 54.76 and 37.97 mg/L nitrite-N, respectively. The 144h LC₅₀ of total ammonia-N and NH₃-N was 36.71 mg/L and 1.04 mgL. The "threshold" of ammonia and nitrite was found at 144h and 120h respectively, from the toxicity curve approaching asymptote. A "safe value" was 3.7 mg/L total ammonia-N, 0.1 mg/L NH₃-N (20 ppt, pH 7.70, 27C) and 3.8 mg/L nitrite-N for P. monodon juvenile .