Studies on the formation of compound yolk in the developing oocytes of an air-breathing fish Channa punctatus (Bloch).

Abstract

1. The process of vitellogenesis in an air breathing fish, Channa punctatus has been studied using histochemical tests for proteins, carbohydrates, lipids and nucleic acids.2. The results indicate two categories of compound yolk formed during vitellogenesis, one-the intravesicular and the other intervesicular yolk.3. The intravesicular yolks develop within yolk vesicles and are composed of polysaccharides including glycogen, protein and RNA. In mature oocytes, these yolks occupy a peripheral position and the smaller variants of such yolk form the cortical alveoli lying just below the vitelline membrane which might participate in the process of fertilization.4. The intervesicular yolks are in the form of spherical globules which fill in most part of the cell except a zone of peripherally displaced PAS positive intravesicular yolk bodies and are mainly composed of proteins and lipoproteins.5. Both nucleolar extrusions and extra-oocytic materials brought into the oocyte by maternal circulation and entering through endocytosis contribute to the formation of intervesicular yolk.6. The appearance of ‘yolk nucleus’ in the early oocytes and its disappearance in mature oocytes is speculated to be involved in the process of yolk deposition.