Investigation of apoptosis and cell proliferation in the esophagus and intestine of pearl mullet (Alburnus tarichi Güldenstädt, 1814) during reproductive migration

In this study, cellular response in the epithelia of the esophagus and intestine of pearl mullet that migrated from the highly alkaline and brackish water of Lake Van to fresh water were investigated by apoptosis and cell proliferation. Toward this aim, the fish were caught from Lake Van or upstream and at the entrance of a stream (Karasu) In the esophagus epithelium, apoptotic cells were observed as randomly distributed and the AI displayed no differences between fish from the lake or the stream. Those cells were determined to increase through the villus epithelium and become localized in the villus tips in the intestine of fish from the freshwater. The AI increased significantly at the anterior or mid-intestine epithelia and throughout the intestine epithelium, whereas it remained unchanged in the posterior intestine epithelium of fish from both upstream and at the entrance of the stream. In the esophagus epithelium, proliferating cells were observed as distributed randomly and the PI values decreased gradually in fish from freshwater. In the intestine, the proliferating epithelial cells were localized mainly in basal areas and troughs of the intestinal folds. The PI increased significantly in the anterior intestine epithelium or throughout the intestinal epithelium of fish collected from the entrance of the stream; however, it did not change along the intestinal epithelium of fish collected upstream. In conclusion, it was observed that cellular changes in the esophagus epithelium during acclimation to freshwater in pearl mullet differed from other euryhaline fish species. Modifications of the cell turnover in the intestinal epithelium during acclimation to freshwater might be related to epithelial permeability, hormonal regulations or oxidative mechanisms during acclimation to freshwater.