Histological structure of the Altai Osman digestive tract, Oreoleuciscus potanini (Cypriniformes: Leuciscidae)

This study focuses on the histomorphological analysis of the digestive tract of the omnivorous ecological form of Altai Osman (Oreoleuciscus potanini Kessler, 1879), an endemic carp species of Central Asia that lacks a morphologically distinct stomach. Four distinguishable sections were identified: esophagus, foregut, midgut, and posterior intestine. The esophagus was characterized by the presence of a multilayered squamous epithelium, an abundance of goblet cells (average 15.6 cells/100 μm), and a thick muscle layer (263.1 μm) consisting of transverse striated muscle. The foregut exhibited the maximum height of the mucosa fold (811.6 m), the height (811.6 μm), columnar epithelium (77.5 μm), and enterocyte nuclei (27.4 μm²), indicating its leading role in digestion and nutrient absorption. The midgut was characterized by a decrease in the fold height (581.7 μm) and an increase in the number of goblet cells (2.9 cells/100 μm) compared to the foregut. The posterior intestine exhibited the lowest fold height but the highest number of goblet cells (5.6 cells/100 μm) and intraepithelial leukocytes (16.4 cells/100 μm). Supranuclear vacuoles were also found in the posterior epithelium. Elements of gut-associated lymphoid tissue (GALT), including intraepithelial leukocytes and eosinophil-like cells, were detected in all parts of the digestive tract. The study revealed histomorphological characteristics of the Altai Osman digestive tract attributable to its omnivorous diet.