Distribution of some endocrine cells in the digestive tract of Van fish ( <scp> <i>Alburnus tarichi</i> </scp> Güldenstädt, 1814) during reproductive migration

The Van fish (Alburnus tarichi Güldenstädt, 1814) is an endemic species of the Lake Van basin, belonging to the Cyprinidae family and exhibiting an anadromous life cycle. Although feeding and growth occur in Lake Van, spawning takes place in freshwater streams entering the lake between April and July, influenced by water temperature. These distinct habitats lead to differences in feeding behaviour and nutritional intake. Fish obtain a limited amount of food from the fresh water in which they breed. This study aimed to characterize the distribution of endocrine cells in the digestive tract of Van fish through morphologic, histologic and immunohistochemical analysis, providing insights into the species' digestive physiology. At the end of the oesophagus, there was a stomach-like structure that served as the stomach. In the continuation of this structure, the anterior and posterior intestines were seen. Although taste buds were observed in the mucosa layer of the oesophagus of fish in the lake environment, no taste buds were found in the oesophagus of fish in the freshwater environment. Immunohistochemical analysis identified gastrin (GAS), cholecystokinin (CCK) and somatostatin (SST) cells within the digestive tract. In freshwater fish, GAS and CCK cells did not react in the oesophagus, whereas in lake fish, GAS, CCK and SST were all detected along the tract. The density and localization of these cells differed based on the parts of the digestive tract and the aquatic areas sampled. The distribution of endocrine cells in the digestive tract of Van fish is influenced by feeding conditions, water physicochemical properties and environmental stress, highlighting the adaptive digestive physiology of this endemic species.