Fine anatomical structures of the intestine in relation to respiratory function of an air-breathing loach, Lepidocephalichthys guntea (Actinopterygii: Cypriniformes: Cobitidae)

Background. The omnivorous freshwater loach, Lepidocephalichthys guntea (Hamilton, 1822)inhibiting unique ecological niche where oxygen content is low. Its alimentary canal is remarkably short, which is surprising considering the fact that this fish is an omnivore. This peculiarity can be correlated with the specific nature of food. Therefore, the aim of the present study was to investigate the mucosal adaptation of the intestine in adult L. guntea with respective digestive- as well as respiratory function. Materials and methods. The surface design of the mucosa of different sections (anterior, mid, and posterior) of the intestine of L. guntea were studied using light and scanning electron microscope following commonly accepted procedures. Results. The mucosa of the anterior intestine was provided with various types of mucosal folds and crowded with almost closely oval or rounded columnar epithelial cells with prominent microridges. The irregular mucosal surface of the mid intestine was exemplified by regularly spaced columnar epithelial cells with minute and prominent microridges/microvilli. On the contrary, irregular mucosal folds with stumpy villi were detected in the posterior intestine. The mucosal surface of that region was made up of columnar epithelial cells containing inconspicuous microridges. In that region the submucosa was provided with increasing number of blood vessels. Various cellular elements in the anterior and mid intestine were accordingly adapted to serve the important functions of absorption and gas exchange. However, the arrangement of low mucosal folds and dense blood capillaries in between the folds in the posterior intestine unequivocally suggested its respiratory role. Conclusion. The micro-architectural pattern and cellular architecture of the anterior intestine and middle intestine of L. guntea unequivocally suggests that these two regions are adapted to serve major role of digestion and absorption process. However, major changes that appear in the posterior intestine are considerably reduction of the absorptive area and the penetration of blood capillaries in between the columnar epithelial cells. Therefore, the posterior intestine of L. guntea is probably adapted to suit its role for aerial respiration. However, further investigation is needed the detailed physiological processes involved for aerial respiration in the region concerned.