Exposure and effect biomarkers indicate health alterations in Aequidens pallidus (Cichliformes, Cichlidae) exposed in situ in degraded Amazonian urban streams

ABSTRACT In the Amazon, the rapid and disorderly occupation of large urban centers resulted in severe degradation of small rivers and streams, resulting in the reduction in abundance of native fish species. This study aimed to evaluate, through an in situ experiment, the effects of water from three differentially degraded urban streams on the health of the widely distributed cichlid Aequidens pallidus. Fish were exposed for seven days to the water of a stream with low anthropic impact signs (A) and two moderately degraded streams (B and C). After exposure, welfare indicators, and genotoxic, biochemical and histopathological biomarkers were analyzed [condition factor (K), hepatosomatic index (HI), erythrocytic nuclear abnormalities (ENA), micronuclei (MN), metallothionein (MT) concentration, and morphological changes to gills and olfactory organ]. Significant reductions were observed in K in fish exposed to B and C, and HI in fish from C. ENA and MN were observed in the fish erythrocytes from the three streams. Reniform nuclei increased significantly in fish from C, as well as MN in fish from B compared to A. MT concentration increased in fish from C compared to A. Lesions in the gills were aneurysms, epithelial detachment, and lamellar fusion. The olfactory organ showed vacuole formation, loss of cilia, and necrosis. Gill and olfactory organ lesion indices were significantly higher in fish from B and C compared to A. The results suggest a high sensitivity of the species to moderately degraded environments and reinforce the need for measures aimed at improving the environmental quality of urban streams.