Study On The Development Of Digestive Tract And Food Selection Of Pelteobagrus Fulvidraco (Richardson)

The development of feeding organs and digestive tract as well as food selection in different stages are studied. The results are as following:1. The size of mouth, morphogenesis of the digestive tract and gut length increase with the growth of this species. The width and height of fish mouth apparently affect the size of food which is intaken.2. On the third day after hatching, the appearance of mandibular arch, hyoid arch(not including basihyoidian cartilage), the first to the fifth branchial arch and branchial stegite prepares for the first feeding in morphogenesis. In 13-day-old fry, the bony development of the pharyngeal skeleton has begun. In 36-day-old young fish, the whole bony development has already finished.3. In the group of feeding larvae, mucosa thickness and muscle thickness of different parts of digestive tract increase with the development of fish. Apart from comparative stability in the number of folds, the height of folds in esophagus, the number and the height of folds in stomach show no apparent law. However, in intestine, they both increase although they have something to do with fullness In stomach, we see no microvilli on the top of the single epithelium while in intestine, the epithelium cell is covered with microvilli, which grows slowly. Goblet cell increases rapidly, especially in stomach and intestine.4. The period of mix nutrition has relationship with temperature. When mean water temperature is between 24 and 26 , the period lasts for about four days(3days old to 6days old); when temperature is between 27 to 28 ,the period lasts for only two days(3days old to 4days old). The first feeding appears on the third day after hatching. The first food of larvae is Rotifera, But if Cladocera predominates in water, the first food can also be small Cladocera . The selection of main food varies with the development of food intake and digestive organs, changing as following sequence: Rotifera in early stage of feeding, then Cladocera first and Copepoda second in postlarval stage, Oligochaeta first intaken in juvenile stage, and then mainly Oligochaeta in young stage.5. Apparent day and night feeding rhythm is observed in larval and juvenile stages. The peak index of fullness lies at 21:00 in prelarval stage, 3:00 in postlarval stage and 6:00 in juvenile stage. The daily feed intake rate varies with the development. In those three stages, the daily feed intake rates are 69.96%, 28.84% and 10.00% respectively.6. Starvation has a great effect on morphology, behaviour, color and histology, especially the histology of intestine. The phenomenon of preying on internal species occurs when size hierarchy or lack of sufficient food exists.