Morphological characterization of embryonic development in Rana catesbeiana

To explore the early embryonic development process of bullfrogs (Rana catesbeiana) and supplement their biological information and imaging data, we obtained the fertilized eggs from artificially bred bullfrogs by natural oviposition to investigate their morphological changes and biological characteristics. The results show that the size of fertilized eggs was (1.41±0.31) mm. At temperature of (24.5±0.4) ℃, the early embryonic development process could be divided into 7 phases and 24 stages. It took 177 h 38 min for the fertilized eggs to reach the operculum closure stage, and the total accumulated temperature was 4 249.71 h·℃. The embryonic development process showed a pattern of a fast speed at the first several stages (From fertilized egg to 64-cell stage) and then a slowdown at the latter stages. When being stimulated by external stimuli, the embryo had an annular contraction response by bending the head and tail. Later, as the embryo hatched until the completion of gill closure, they become tadpoles.