Embryonic and Early Larval Development of Snow Trout Schizothorax richardsonii (Grey): A Research Note

The embryonic and larval developments of the snow trout Schizothorax richardsonii, an inhabitant of the Himalayan region, were documented in the present study. The telolecithal eggs were translucent, and the chorion and vitelline membranes were separated by perivitelline space. In the zygote, after 1 h of fertilization (HAF), the perivitelline space widened toward the animal pole compared to the vegetal pole. The meroblastic cleavage started at 2 HAF, and the first cleavage furrow divided the zygote into two blastomeres. After successive cleavages, the number of cells increased, and the size of blastomeres became smaller and more variable. The embryo reached a high stage at 12 HAF. Epiboly started at 17 HAF, and 90% epiboly was recorded at 44 HAF. The segmentation of the embryo started at 46 HAF. Hatching was recorded at 125 HAF at 11.8–12.6 °C. The newly hatched larvae were translucent (1.5 ± 0.6 mg) with a ventrally located mouth and undifferentiated digestive tracts. The swim bladder appeared, and anus opened on day-5 after hatching (DAH). The sequence of fin formation was as follows: caudal, pectoral, dorsal, anal, and pelvic fins. The exogenous feeding started on day 8 after hatching, and the yolk sac was depleted on day 9. The average weight of 32 DAH larvae was 54.38 ± 7.8 mg.