STUDIES ON THE ANATOMY AND HISTOCHEMISTRY OF THE DIGESTIVE TRACT IN THE FINGERLING STAGES OF THE GRASS CARP, CTENOPHARYNGODON IDELLA (VALENCIENNES), IN RELATION TO FOOD AND FEEDING HABITS.

The anatomy and histochemistry of the digestive tract of the fingerling stages of the grass carp, Ctenopharyngodon idella (Valenciennes) described. The observed qualitative and quantitative differences along the tract indicate a high degree of specialization of each segment for specific digestion and absorption. The results revealed that the mouth is relatively
large, semiventral and is bounded by the upper and lower lips. The lips consist of an outer layer of epidermis and an inner layer of dermis. The epidermis is formed of stratified epithelium provided with numerous taste buds and mucus-secreting cells. The latter stain blue-red with. Alcian blue and periodic acid Schiff (PAS) indicating the presence of neutral
mucopolysaccharides (MPS). The dermis consists of two layers: an outer well developed stratum compactum and an inner thin layer of reticular connective tissue. Pigment cells and blood capillaries are of common occurrence in the dermal layer.
The mouth leads into the bucco-pharynx through the dorsal maxillary valve, lying just behined the dorsal lip. The tongue is poorly developed and does not contain muscle fibers. The wall of the buccopharynx is made up of mucosa and submucosa, and in some places of a third layer, the muscularis. The mucosa consists of stratified squamous epithelial layer, containing taste buds. The mucus - secreting cells are so abundant that in certain cases they
occupy the entire epithelial surface. They decrease gradually towards the posterior direction.Their contents stain blue and red with Alcian blue and PAS indicating their acid and neutral MPS contents. Taste buds are much mumerous in the anterior portion than in the posterior one. The submucosa consists of stratum compactum and a layer of loose areolar connective tissue, richly supplied.