Through the integration of chemical, biochemical and morphological analyses, this study investigated the
effects of multiple pollutants on environmental biomarkers, such as gill histopathological changes and
hematological and biochemical parameters, in Oreochromis niloticus exposed to four sites in the Jacuipe
and Subaé rivers over seven days. Sediment analyses identified Sapelba as the most contaminated site,
followed by Oliveira de Campinhos, Santo Amaro and Jacuípe. Water analyses revealed aluminum, iron
and manganese at all sites. Aluminum and other metal were also detected in the gills of fishes. Fish
exposed to the Sapelba site exhibited significant necrosis formation, as well as higher hematological
parameters and trend to increase of cortisol levels. However, filament epithelium proliferation was
higher at the Oliveira de Campinhos and Santo Amaro sites, at which the lowest levels of the
hematological variables were observed. Multivariate analysis grouped some gill histopathological
changes together, such as epithelial detachment with edema and lamellar epithelial proliferation with
the lamellar fusion of adjacent filaments, revealing relationships among them. Positive associations were
identified between sediment contamination and necrosis and cortisol, while water contamination was
related with filament epithelium proliferation, aneurism, lamellar fusion and several hematological
parameters. Furthermore, relationships between blood parameters and gill histopathological changes
demonstrated a joint physiological response that may have resulted from environmental variables such
as dissolved oxygen. The results exhibited the direct influence of xenobiotics on these biomarkers but
also highlighted the need to consider the complexity of environmental factors to optimize the adoption
of these environmental predictive tools.