Histopathology and immunohistochemistry of gills of Van fish (Alburnus tarichi Güldenstädt, 1814) infected with myxosporean parasites.

The Van fish are a cyprinid species endemic to Turkey's largest soda lake, Lake Van, and have great economic value because they are a food source. Once a year, the fish take part in reproductive migration to the fresh waters flowing into the lake. The fish migrate from an extreme environment with high salinity (2.2%) and high pH (9.8). These fish are unable to reproduce in this alkaline environment and must migrate to fresh water during their breeding season. The aim of the present study is to report the presence of the myxosporean parasites on the gills and the pathological changes. Changes in gill histopathology, mucocytes, mitochondria-rich cells, expression of Heat Shock Protein 70 (Hsp70), and ATPase (NKA) were observed in the gill tissue. As a result of the histopathological changes in gills, infected fish had abundant plasmodia with different sizes. Plasmodia were found on gill filaments inside white ovoid-shaped structures. It was observed that plasmodia were contained on the primary filament which changed the histological structure of the gill tissue to a large extent. It was determined that the density and size of mucocytes in the infected areas of the gill tissue increased, whereas the number of mitochondria-rich cells decreased. Hsp70, an indicator of stress, was not different between normal and infected fish.