ONTOGENY OF THE DIGESTIVE TRACTS IN GRASS CARP (CTENOPHARYNGODON IDELLUS), YELLOWCHECK CARP(ELOPICHTHYS BAMBUSA) AND TOPMOUTH CULTER(CULTER ALBURNUS)

A thorough understanding of the temporal process of structure and function of larval and juvenile digestive systems has important values for investigating the digestive characteristics, nutritional needs of larva and juveniles, and enhancing their survival and growth. In inland aquaculture in China, grass carp Ctenopharyngodon idellus, yellowcheck carp Elopichthys bambusa and topmouth culter Culter alburnus are economically important freshwater species that belong to the family Cyprinidae, with entirely different nutritional needs. Using the methods of histology, a comparative study among the above species in early developmental stages was conducted in our study to examine the ontogeny of digestive tracts. The results of the three species in different days post hatching (dph) showed the following: (1) yellowcheck carp had the maximum relative bulk of yolk sac in newly hatched larva in the three species; (2) the intestinal tubes and oral fissures of the three species were differentiated apparently at 2 dph and 3 dph, and intestinal cavities of grass carp, yellowcheck carp and topmouth culter appeared at 3 dph, 4 dph, and 2 dph, respectively; (3) the food pulps were observed inside the intestines of grass carp, yellowcheck carp and topmouth culter in 4 dph, 7-9 dph, and 4 dph, respectively, indicating that these larval species had initiated exogenous feeding at different times post hatching; (4) mucosal folds of intestines in grass carp, yellowcheck carp and topmouth culter were initially differentiated at 5 dph, 6 dph and 6 dph, respectively, and subsequently the number and height of mucosal folds has been increased at different degrees with the development of larvae and juveniles, enabling the fishes to increase the total mucosal surface areas during development; (5) the intestinal coiling of grass carp and yellowcheck carp was initially observed from the transverse slices at 14 dph and 30 dph respectively, but no intestinal coiling appeared during the experiment at 30 dph in topmouth culter; (6) grass carp, yellowcheck carp and topmouth culter were observed to have numerous intestinal mucous cells at 17-23 dph, 30 dph and 24-29 dph, respectively, indicating that the conversion or the divergence of feeding habits within a specific species or between different species had been generally accomplished.