Efeito agudo dos compostos nitrogenados, amônia e nitrito, na fase larval de colisa lalia (Trichogaster lalius)

Abstract

Ornamental aquaculture plays a significant role in Brazil’s aquaculture sector. Among the species cultured, the dwarf gourami, Trichogaster lalius, stands out for its economic value and popularity among aquarists. However, the deterioration of water quality, particularly the accumulation of nitrogenous compounds such as total and un-ionized ammonia and nitrite, represents a major threat to fish health. This study aimed to evaluate tolerance through acute toxicity tests with ammonia and nitrite during the larval stages of T. lalius, using mortality rates to determine the 96-hour median lethal concentration (LC₅₀) and to analyze histopathological alterations in gill tissues. The tests were conducted in duplicate under controlled laboratory conditions, using 240 animals (average weight 0.0542 g) distributed across 24 containers of 1.5 L. LC₅₀ values were estimated using the Trimmed Spearman- Karber method. The results showed a progressive increase in mortality with higher tested concentrations of both nitrogenous compounds. The 96-hour LC₅₀ values were 3.04 mg/L N-AT and 0.30 mg/L N-NH₃ for ammonia, and 2.35 mg/L N-NO₂⁻ for nitrite, with estimated safe levels of 0.030 mg/L N-NH₃ and 0.23 mg/L N-NO₂⁻, respectively. Histological analyses revealed significant gill alterations, including lamellar fusion, epithelial hyperplasia and hypertrophy, epithelial detachment, and dilation of the blood sinus. These lesions were more severe and frequent at higher compound concentrations. The results reinforce the importance of rigorous water quality management in ornamental aquaculture, particularly regarding nitrogenous compounds, which can severely compromise survival and welfare during the early developmental stages of fish.

Keywords: Water quality, Histopathology, Ornamental fish, LC₅₀, Larval stage, Gill.