The process by which the zygote divides repeatedly into a full-fledged organism is called fertilization. This is done in three steps.
(i) Embryonic cleavage: Cleavage begins 30-45 minutes after formation of the zygote. The zygote divides by cleavage to form micromere and macromere cells. In the process of blastulation, these cells become blastomeres. Blastomere cells are arranged in a certain layer. During gastrulation, blastomere cells are arranged in three layers. Ectoderm, Mesoderm and Endoderm.
(ii) Hatching of larval stage: Larva emerges from egg within 15-18 hours. The larva is called an egg. Dimpona age of 72 hours is called renupona. In this condition, the embryo takes on a light yellow color. Notochord and nerve cord are formed. Eyes, hearing and chromatophores are formed. Air sacs and digital fins are present.
(iii) Post larval hatching: In this stage the yolk sac is destroyed. Operculum, dorsal fin, caudal fin etc. arise. Air sacs are divided into two parts. The tail is homocircular. The nostrils are fully divided, the eyes are equal and the fleshy mouth is formed.