Comparison of early developmental stages, yearly growth and morphology of grass carp, Ctenopharyngodon idellus, Wu-chang fish, Megalobrama amblycephala, and their hybrid. In：R. Hirano and I. Hanyu (eds.)

Abstract

This study was conducted to compare the early developmental stages, yearly growth and morphology of the hybrid grass carp, Ctencloharynaodon idellus 1.19aalobramai samblyceprialA and the female parent, grass carp, c. idellus. Where sufficient data were available, the study also compared the hybrid with the male parent, h. amblycePhala, or Wu-Chang fish. Fertilization rates were as high as 95% and the hatching time was about 30 hours at 21-24'C for both grass carp and the hybrid. The percentage of malformation in the embryonic development was lower and the hatching rate was higher in the.grass carp. The larval growth rates of the two groups were the same till the eighth day after hatching, but in the following weeks, larvae of grass carp grew faster. During a culture period of 17 months, growth of the hybrid in terms of body length was found to be the same as that of grass carp. Survival rates for grass carp and the hybrid were 98.5% and97.0%, respectively. Although the external apoearance of the hybrid bore closer resemblance to the female parent, most of the hybrid's morphological characteristics were a cross between those of the parents.