A HISTOLOGICAL STUDY OF THE DEVELOPMENT OF THE DIGESTIVE-TRACT OF SIBERIAN STURGEON (ACIPENSER BAERI) DURING EARLY ONTOGENY

Histological development of the digestive tract of Siberian sturgeon d uring early life stages (1-21 days post hatch) was studied using light microscopy. At hatching, the digestive tract is represented by a gast ric cavity filled with yolk and lined by endodermal cells, and a parti ally differentiated hindgut; and does not communicate with the exterio r as the mouth and anus are not yet opened. During the endogenous feed ing phase, yolk sac resorption, stomach differentiation into a gizzard and glandular region, and the development of the anterior, intermedia te region and spiral valve of the intestine are the most conspicuous e lements of development. At onset of exogenous feeding (9 days post hat ch), yolk sac reserves are not completely depleted from the cardiac st omach, suggesting a period of mixed nutrition. Fat is accumulated in t he anterior and intermediate regions of the intestine confirming the g reater resistance of larvae to long periods of starvation. At this tim e, the alimentary canal presents the morphological digestive features characteristic of juvenile and adult stages. The buccopharynx is lined by a pseudostratified cylindrical epithelium with teeth and numerous taste buds. The esophagus is constituted by ciliated and mucous cells which are organised in two different regions. The non-glandular stomac h presents a simple columnar epithelium and a prominent tunica muscula ris, while the glandular stomach epithelium consists of cuboidal cells , with numerous simple and tubular gastric glands. The anterior and in termediate regions of the intestine are similar, lined by a columnar c iliated epithelium and can be distinguished by the major number and si ze of mucosal folds and level of vacuolisation of the intermediate int estine. The spiral valve is lined by a simple columnar ciliated epithe lium with supranuclear vacuoles. Present results reveal that the ontog enetic development of the digestive tract of Siberian sturgeon is simi lar in comparison with other Acipenserid species. However, there exist several differences referred to the differentiation time of some dige stive structures, such as the differentiation of the pyloric and cardi ac stomach, the development of gastric glands, and the acquisition of an anatomically alimentary canal similar to those of juveniles and adu lts, which affect first feeding time and, the rearing and husbandry of Siberian sturgeon larvae. (C) 1998 Elsevier Science B.V. All rights r eserved.