This article is dedicated to the periods of Rainbow trout`s embrional development beginning from fertilization till getting out from the egg. Research has been carried out on materials of Chukhur -Kabala fish factory of Azerbaijan. Morphological changes of the embrional development inside the egg are divided into seven periods. Each period differs from the previous one according to form and essence. Duration of these periods is varies according to the environment, especially to temperature, cleanness, degree of oxygen supply of the water where eggs develop.