Fish Gills Alterations as Potential Biomarkers of Environmental Quality in a Eutrophized Tropical River in South-Eastern Brazil

Gill anomalies in three common fish species of different taxonomic order, habitat dwelling and feeding habits (one Characiformes, Oligosarcus hepsetus; one Siluriformes, Hypostomus auroguttatus; and one Perciformes, Geophagus brasiliensis) from a eutrophized tropical river in south-eastern in Brazil were compared. The aim of this study was to search for sentinel species that could be used as potential biomarkers of environmental quality. Most fish had gills with histological changes, namely epithelial lifting, interstitial oedema, leucocyte infiltration, hyperplasia of the epithelial cells, lamellar fusion, vasodilatation and necrosis. On the other hand, lamellar blood congestion and lamellar aneurysm, which are more serious and often irreversible changes, were recorded for the water column carnivorous O.similar to hepsetus and, to a lesser extent, for the bottom-dwelling detritivorous H.similar to auroguttatus. A histopathological alteration index (HAI) based on the occurrence and severity of gills anomalies indicated that O.similar to hepsetus (mean score similar to=similar to 11.4) had significantly higher values (KruskallWallis H2,41 similar to=similar to 15.95, P similar to=similar to 0.0003) compared with G.similar to brasiliensis (mean score similar to=similar to 7.0). Overall, the omnivorous G.similar to brasiliensis had comparatively lesser occurrence of most gill anomalies compared with other two species, being less suitable as biomarker of environmental quality. In contrast, the water columndweller O.similar to hepsetus (water column) and the bottom-dweller H.similar to auroguttatus had gills most susceptible to changes, making them more suitable for using as histological biomarkers of the environmental quality in entrophized tropical rivers.