Acute toxicity of ammonia to various life stages of the Amazon river prawn, Macrobrachium amazonicum, Heller, 1862

The buildup of nitrogenous wastes in the water reflects biological processes potentially stimulated by organic pollution. These wastes may cause physiological harm and even mortality in produced aquatic species. This study aimed at determining the effects of ammonia on different life stages of the Amazon river prawn Macrobrachium amazonicum. Experimental set-up used 240 prawns to each life stage (post-larvae, juveniles and adults), stocked in 24 experimental units, under a totally casualized arrangement, for each life stage. Individuals were exposed to 6 different concentrations of total ammonia (0, 5, 10, 20, 40 and 80 mg·L− 1), and the mean lethal concentration after 96 h was determined (LC50-96 h). Water oxygen, pH, and temperature were monitored daily; at the start and end of the experimental periods, hardness, alkalinity, ammonia, nitrite and nitrate were also measured. LC50-96 h was calculated through the probit method, later submitted to a linear regression (p < 0.05). LC50-96 h for post-larvae, juveniles, and adults of M. amazonicum was of 21.14, 21.65 and 36.59 mg·L− 1 of total ammonia, or 0.67, 0.75 and 1.08 mg·L− 1of non-ionized ammonia. Thus, from these results, safe levels for the production of this prawn are of 0.06, 0.07 and 0.1 mg·L− 1, from post-larvae, juveniles and adults, respectively.