Acute Toxicity of Ammonia and Nitrite to Painted River Prawn, Macrobrachium carcinus, Larvae

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AbstractThis study evaluated the toxicity of ammonia and nitrite to different larval stages of Macrobrachium carcinus. Three replicated groups of larvae in the zoea stages II, V, and VIII (hence named Z2, Z5, and Z8, respectively) were exposed separately to five ammonia (5, 10, 20, 40, and 80 mg total ammonia nitrogen [TAN]/L) and six nitrite concentrations (5, 10, 20, 40, 80, and 160 mg NO2‐N/L), plus a control treatment with no addition of ammonia and nitrite, at a salinity of 20 g/L. The ammonia LC50 values at 96 h for Z2, Z5, and Z8 were 8.34, 13.84, and 15.03 mg TAN/L (0.50, 0.71, and 0.92 mg NH3‐N/L), respectively, and the nitrite LC50 values at 96 h for Z2, Z5, and Z8 were 3.28, 9.73, and 34.00 mg NO2‐N/L, respectively. The estimated LC50 values for NO2‐N were lower than those for TAN in most of the stages evaluated. This observation suggests that M. carcinus larvae are more tolerant to ammonia, except at Z8, in which larvae had a higher tolerance to nitrite. Based on the lethal concentrations at 96 h, it may be concluded that the tolerance of M. carcinus to ammonia and nitrite increases with larval development. Safe levels were estimated to be 0.834 mg TAN/L (0.05 mg NH3‐N/L) and 0.328 mg NO2‐N/L; therefore, efforts should be made to maintain lower concentrations of these compounds throughout the larval rearing of M. carcinus.