TOXICIDADE AGUDA DA AMÔNIA E DO NITRITO PARA JUVENIS DO PAMPO Trachinotus marginatus (CUVIER, 1832) EM DIFERENTES SALINIDADES.

by Fonseca Costa, Luiza Dy

The present study was conducted to estimate the acute toxicity of ammonia-nitrogen (NH3-N) and nitrite-nitrogen (NO2--N) to juvenile pompano Trachinotus marginatus(0.86 ± 0.21 g) at different salinity levels: 5, 10 (equivalent to its isosmotic point), and 30?. Fish were acclimated to the different salinities for 10 days and fed in excess daily. Groups of five fish (0.86 ± 0.21 g) were exposed to five concentrations of NH3-N and NO2--N for 96 h plus control groups for each salinity in three replicates where no toxicant was added, measured concentrations ranged from 0.28 to 3.53 mg NH3-N/L and 24.8 to 191.1 mg NO2 --N/L. Tests were run using a standard semi-static system with 100% daily renewal of water and toxicants. The results were based on mortality data registered in different concentrations tested, using the software Trimmed Spearman Karber method. The median-lethal concentrations (LC50) after 96 h of exposure to NH3-N were 0.66 (0.53-0.81), 1.87 (1.65-2.12) and 1.06 (0.94-1.20) mg NH3-N/L for 5?, 10?, and 30?. The LC50 -96 h to NO2--N were 39.94 (36.39-43.84), 116.68 (112.52-121.00) and 37.55 (20.91-67.44) mg NO2--N/L for?, 10?, and 30 ?. Acute toxicity of NH3-N and NO2--N to pompano was affected by salinity. Results of the present study show that pompano reared at an isosmotic environment are less sensitive to NH3-N and NO2- -N. Tolerance to NH3-N is compromised at reduced salinities, while toxicity of NO2--N is similar at 5 and 30 ?.