Efeito letal da amônia e do nitrito nas fases iniciais da vida do Betta splendens

The presence of nitrogen compounds within aquaculture production systems has gained importance today, the lack of knowledge of the limits of tolerance of the species produced to these compounds can cause great damages at the end of the crop. Thus, the present study aimed to identify the LC50 values (96h) for ornamental Betta splendens at three different ages, 7, 21 and 45 days of life, exposed to increasing concentrations of total ammonia 0, 35, 42, 50, 65 And 80 mg-L; 0, 50, 65, 80, 87 and 95 mg-L; 0, 125, 135, 145, 155 and 165 mg-L respectively and increasing concentrations of nitrite, 0, 25, 50, 75, 100 and 125 mg-L; 0, 50, 75, 100, 125 and 175 mg-L; 0.120, 160, 200, 240 and 280 mg-L respectively and to estimate the safety level of the nitrogen compounds for this species. The experiment was performed in a semi-static system and each treatment was performed in duplicate. 10 7-day fish were kept in beakers of 1 L for 96 h at a temperature of approximately 28 ± 0.15 ° C; PH 7.2 ± 0.2; Oxygen 5.9 ± 0.28 mg-L; Alkalinity 77.5 ± 10.60 mg / L. 10 animals in the Betta experiments of 21 and 45 days of life, where they were kept in beakers of 2L for 96 h temperature 28,1 ± 0,11 °; 28 ± 0.13 ° C, pH 6.9 ± 0.4; 6.9 ± 0.1, oxygen 6.2 ± 0.23; 6.7 ± 0.27 mg / L, alkalinity 85.7 ± 12.0; 79.5 ± 9.45 mg / L respectively. The "Trimmed Spearman Karber method" program was used to estimate the median lethal concentrations LC50 (96h). During the experiment animals were collected for histological analysis at the different concentrations tested and were analyzed by optical and scanning microscopy. The CL'50 for the ages 7, 21 and 45 days were estimated for ammonia as being at, 36.87 mg / L; 61.19 mg / L; 132.94 mg / L respectively and for nitrite as - 141.96 mg / L N-NO2-. It was possible to observe histological changes in the gills of the animals in the different concentrations tested. The histopathological study revealed frequent alterations in the three different ages of the studied species. The most frequent damages were: epithelial elevation, hyperplasia, hypertrophy and lamellar fusion of the epithelial cells. By means of the results, it can be concluded that the Betta splendens ornamental fish is very tolerant to the nitrogen compounds and the incidence of the histopathological changes in the gills indicate the animals' compromise when exposed to high concentrations of nitrogenous compounds in the water.