Developmental stages and germ cell lineage of the loach (Misgurnus anguillicaudatus).

The staging of embryonic and larval development, and the germ cell lineage of the loach, Misgurnus anguillicaudatus, are described. Fertilized eggs were obtained by artificial insemination. For the convenience of detailed observation and photography of the external appearance, we use dechorionated embryos. Through a series of operations, these embryos were cultured at 20 degrees C in an incubator. Embryonic and larval development of the loach was divided into five periods: cleavage, blastula, gastrula, segmentation, and hatching. Stages were assigned within each of these periods. Developmental stages were determined and named by morphological features and somite number. The staging series were photographed and tabulated. The germ cell lineage was then elucidated by whole mount in situ hybridization of mRNA expression of the germ-cell-specific marker vasa and histological analysis. Primordial germ cells (PGCs) of the loach derived from the cleavage furrows of 8-cell stage embryos began proliferation in the late blastula period and migrated to the gonadal anlagen through a migration pathway similar to that of the zebrafish. However, it is characteristic of the loach that PGCs migrate a long distance and stay in the posterior part of the yolk-extension region.