Effects of acute toxicity and sublethal nitrite levels on oxidative and histopathological stress parameters in juveniles of Paralichthys orbignyanus sole
This study evaluated the acute toxicity and sublethal effects of nitrite on oxidative stress and histopathological parameters of early juvenile Brazilian flounder Paralichthys orbignyanus. Fish were exposed to control, 20, 40, 80, 160, 320 and 640mg NO2-N.L-1, in triplicate for 96h. Every 24h the tanks were monitored to check possible mortality to estimate the LC50. At the end of the experiment, fish were collected for stress oxidative and histopathological analysis. The LC ranged from 427.8 to 393.1mg NO2-N.L-1 for 24 and 96h, respectively. ACAP showed gradual reduction in fish exposed to nitrite levels from 160mg NO2-N.L-1. GST activity was higher in 80, 160 and 320mg NO2-N.L-1. NPSH and PSH levels were higher in 160 and 320mg NO2-N.L-1 compared to the Control, 20 and 40mg NO2-N.L-1. TBARS level was significantly higher in fish exposed to 320mg NO2-N.L-1than the Control and 20mg NO2-N.L-1. No histopathological changes were evidenced in the gills and liver of exposed fish. Moreover, a pro-oxidant condition was induced when P. orbignyanus were exposed to concentrations from 80mg NO2-N.L-1, which was evidenced by alterations in the antioxidant system and increased levels of oxidative damage. Therefore, it is recommended that the concentrations in the environment do not exceed 40mg NO2-N.L-1 in order to avoid oxidative stress in this species.