<p>Van fish live in Lake Van, which has different physicochemical properties from freshwater and seawater ecosystems. Every year, Van fish migrate from Lake Van, which has extreme physicochemical properties, to the freshwater flowing into the lake to reproduce. During this migration, they are exposed to stress due to the different properties of the aquatic habitats. In this study, changes in the kidney tissue of Van fish during the spawning migration downstream and in freshwater were examined morphometrically, histologically, biochemically, and immunohistochemically. It was observed that proximal tubule area and diameter, collecting duct area and diameter, glomerulus area, Bowman’s capsule area, and glomerulus numbers changed in the kidneys of fish sampled from downstream and freshwater. Na + /K + ATPase transmembrane proteins (NKA) and apoptotic cells were immunohistochemically labeled in both aquatic areas in the kidney tissue. While relative cells containing NKA were determined to be dense in stream samples, apoptotic cells were determined to be more numerous in the kidney tissue sampled from the downstream environment. Plasma urea, uric acid, and sodium were high in downstream, while creatinine, chloride, magnesium, and potassium were also high in freshwater. As a result, it was determined that changes in the morphological structure and histology of the kidney tissue of Van fish were necessary for adaptation in different aquatic habitats.</p>