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

This 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 Z 2 , Z 5 , and Z 8 , 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 NO 2 ‐N/L), plus a control treatment with no addition of ammonia and nitrite, at a salinity of 20 g/L. The ammonia LC 50 values at 96 h for Z 2 , Z 5 , and Z 8 were 8.34, 13.84, and 15.03 mg TAN /L (0.50, 0.71, and 0.92 mg NH 3 ‐N/L), respectively, and the nitrite LC 50 values at 96 h for Z 2 , Z 5 , and Z 8 were 3.28, 9.73, and 34.00 mg NO 2 ‐N/L, respectively. The estimated LC 50 values for NO 2 ‐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 Z 8 , 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 NH 3 ‐N/L) and 0.328 mg NO 2 ‐N/L; therefore, efforts should be made to maintain lower concentrations of these compounds throughout the larval rearing of M. carcinus .