A multi-tissues comparison of biomarkers in Serrasalmus rhombeus (Teleostei: Serrasalmidae) and Prochilodus nigricans (Teleostei: Prochilodontidae) from two Amazonian rivers with distinct levels of pollution

Aquatic ecosystems are often exposed to a complex mixture of pollutants that can have a negative influence on the health of the resident organisms. In this context, it is crucial to understand the biological responses of the different organisms that inhabit impacted areas to identify biomonitors that are representative of alterations in the local biota. In the present study, two fish, Serrasalmus rhombeus (red-eyed piranha) and Prochilodus nigricans (curimatã) were assessed as potential biomonitors for Amazonian rivers. A total of 121 fish of these two species were collected during the dry season from two rivers representing different extremes of pollution. One site was the Xingu River, which has low level of pollution, while the other was the Itacaiunas River, which is impacted by high levels pollution from multiple sources. Two exposure biomarkers (glutathione S-transferase activity and total antioxidant capacity) and one effect biomarker (lipid peroxidation) were evaluated in samples of both species extracted from various types of tissues (brain, liver, gills and muscle). The results of the analyses indicated the occurrence of both species-specific and tissue-specific responses. The responses of the biomarkers of the detritivorous species, P. nigricans, were more significant than those of the apex predator, S. rhombeus. In addition, the P. nigricans specimens from the polluted (Itacaiunas) river presented marked suppression of the responses related to the detoxification and antioxidant defences, which resulted in more significant oxidative damage (lipoperoxidation) in comparison with the less polluted (Xingu) river. These findings indicate that P. nigricans is the more sensitive of the two species and would thus be the better choice as a biomonitor for environmental monitoring. The results of the present study also indicate that a more integrated approach to the assessment of the response of biochemical biomarkers, including the analysis of a range of different types of tissue should be adopted to guarantee the robustness of analyses of environmental quality