In order to contribute developmental technology, the early embryonic stages during the pre-gastrula were studied by cytological, histological or biochemical viewpoints in goldfish Carassius auratus.
Synchronous cleavages occur 9 times every about 30 min from 50 min to 6 h post-fertilization at 20°C, and, thereafter, transpose asynchronous phase, suggesting mid-blastula transition (MBT). This timing is staged as the mid-blastula. Genomic expression of mesodermal markers, goosecoid and no tail, are detected with in situ hybridization assay from 8 h post-fertilization. This timing is staged as the late-blastula. Cytoplasmic protrusions as cell movement are ovserved after MBT, and autonomous mixing of blastomeres from the late-blastula stage. Deep cells were produced from the surface part of blastomeres and central part of yolk cell during the late-blastula stage. Marginal yolk syncytial layer forms during the mid-blastula stage, but central yolk syncytial layer forms after the late-blastula stage. This result suggests that each yolk syncytial layer has a different origin of nuclei.