The nitrogen is derivates in water presence indicates active biological processes influenced by organic pollution, being able, in high concentrations, to cause physiological damages, even mortality in aquatic organisms. In order to determine the lethal effect of the un- ionized ammonia and of the nitrite, fingerlings of cará (Cichlasoma facetum) have been exposed, during 96 hours, to diverse concentrations of such composites: from 0 to 4.60 mg.L-1 of NH3 N, and from 0 to 6.68 mg.L-1 of NO2. The calculated CL50, for 96 hours, was 2.95 mg.L-1 of un-ionized ammonia. The highest concentration of nitrite, 6.68 mg.L-1, caused the mortality of 45.63% of the fingerlings of cará in 96 hours. The factorial analysis of the mortality variance in relation to the concentration of agents, showed the interaction between both products, resulting the increase of mortality of fingerlings of cará.
Nitrite; ammonia; toxicity; Cichlasoma facetum
