Morphological changes in the kidney of a fish living in an urban stream.

This study reports the incidence of histological alterations in the posterior kidney and morphometric changes in the interrenal tissue of the Neotropical fish Astyanax altiparanae collected from an urban stream impaired by anthropogenic activities and from a clean site (reference). The histological alterations observed in fish kidney from the disturbed stream were in complete contrast to those from the reference site, in respect of the type, severity and number of lesions observed. Tissue lesions found in fish from the urban stream were more severe and in some cases irreparable. The morphometric analysis of interrenal cells showed that fish from the urban stream exhibited increased cellular and nuclear areas and nuclear diameter, indicating hyperactivity of the interrenal cells, which is a sign of long-term stimulation of the hypothalamus-pituitary-interrenal axis. The high incidence of histological alterations in the kidney of A. altiparanae is an evidence of the poor environmental quality of this urban stream, while interrenal cells hypertrophy indicates that these fish are chronically exposed to stressors in their environment. Although the specific causative factors for the observed alterations are unknown this study demonstrates the application of kidney histopathology as a general quality indicator of the aquatic environment.