Histochemical changes, cellular dynamics and antioxidant responses in the corpuscles of Stannius of the female Lake Van fish ( Alburnus tarichi Güldenstädt, 1814) (Cyprinidae) during migration from highly alkaline and brackish water to freshwater

Abstract

The Lake Van fish (Alburnus tarichi) is an anadromous species, which is endemic to Lake Van Basin of Turkey. In spring, the fish migrates from Lake Van, which has highly alkaline and brackish water, to freshwater to spawn. During the anadromous migration of the female Lake Van fish, histochemical changes in the cell types, cellular dynamics, apoptosis, cell proliferation and antioxidant responses in the corpuscles of Stannius (CS) which are tiny endocrine glands related with calcium homeostasis were examined. When compared to the lake, calcium concentrations of ambient water and plasma increased considerably in freshwater. Freshwater dramatically increased the number of predominant type-I cells in the gland while decreased the type-II cells. A reduction in the cytoplasmic periodic acid-Schiff content of type-I cells was observed in freshwater. No cytoplasmic staining was found in cytoplasm of type-II cells in both lake and freshwater. Apoptotic cells were detected in fish sampled from both the lake and freshwater and a nonsignificant increase was observed in freshwater. The number of proliferating cells increased significantly in the freshwater, as well as antioxidant defences such as catalase, glutathione peroxidase and glutathione s-transferase activities, which indicates an elevated oxidative status. The findings suggest that type-I cells are possible source of a hypocalcin hormone and type-II cells are considered to be a likely precursor of type-I cells. Apoptosis and cell proliferation are basic mechanisms of gland remodelling. In addition antioxidant mechanisms play a role during the acclimation of the gland in different environments.