Biomarcadores de exposição e efeito indicam alterações na saúde do peixe Aequidens pallidus (Cichliformes, Cichlidae) após exposição in situ em igarapés urbanos

Abstract

Urban areas generate and release domestic and industrial effluents into the aquatic environment. In the Amazon, the rapid and disordered occupation of large cities, like Manaus, resulted in the severe degradation of small streams, known regionally as igarapés. As a consequence of this degradation, the fish fauna has been deeply affected and there is a reduction in the abundance of native species of streams in the region, such as the fish Aequidens pallidus (Cichliformes: Cichlidae). In this context, there is a need for studies that provide information about the sublethal effects of water in the Manaus streams. Such information is essential for the definition of conservation strategies for the species and can also be used in the elaboration of public policies that aim to reverse the current situation of urban streams. Therefore, the objective of this study was to evaluate the toxicological effects of water from urban streams on the health of Aequidens pallidus through an in situ experiment. Three urban streams were selected: one intact (A) and two impacted (B and C). The fish were exposed to each stream for seven days. Biomarkers of effect as genotoxic, histopathological, condition factor (K) and the hepatosomatic index (IHS), as well as the exposure biomarker: metallothioneins (MTs) were analyzed. Limnological parameters of the water were also checked and samples were obtained for analysis of dissolved metals. A reduction in K was observed in fish confined in streams B and C, while IHS was reduced only in fish from stream C. In fish erythrocytes, erythrocytic nuclear abnormalities (ANEs) and micronuclei (MN) were observed. From the ANEs, a significant increase in reniform and vacuolated nuclei was observed. MN frequencies, MT concentrations, and gill and olfactory organ injury index were higher in fish from streams B and C. Lesions such as aneurysms, epithelial detachment and lamellar fusion were observed in the gills, and vacuole formation, loss of cilia and necrosis in the olfactory organ. The results suggest a high sensitivity of the cichlid Aequidens pallidus upon exposure to degraded environments and indicate damage to the health of individuals, representing the possibility of severe ecological damage since the species is at the top of the food chain and prevents the invasion of non-native species in the streams. These results reinforce the need to take measures to reduce pollution in the streams of Manaus, in order to contain their harmful effects and to promote the health of native fish species.