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 80mg total ammonia nitrogen [TAN]/L) and six nitrite concentrations (5, 10, 20, 40, 80, and 160mg NO2-N/L), plus a control treatment with no addition of ammonia and nitrite, at a salinity of 20g/L. The ammonia LC50 values at 96h for Z(2), Z(5), and Z(8) were 8.34, 13.84, and 15.03mg TAN/L (0.50, 0.71, and 0.92mg NH3-N/L), respectively, and the nitrite LC50 values at 96h for Z(2), Z(5), and Z(8) were 3.28, 9.73, and 34.00mg 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 Z(8), in which larvae had a higher tolerance to nitrite. Based on the lethal concentrations at 96h, it may be concluded that the tolerance of M. carcinus to ammonia and nitrite increases with larval development. Safe levels were estimated to be 0.834mg TAN/L (0.05mg NH3-N/L) and 0.328mg NO2-N/L; therefore, efforts should be made to maintain lower concentrations of these compounds throughout the larval rearing of M. carcinus.