The reproductive biology and the histological and ultrastructural characteristics in ovaries of the female gadidae fish Merluccius merluccius from the Egyptian Mediterranean water
AbstractMonthly analysis of the maturity stages distribution revealed that the gadidae fish Merluccius merluccius has a long spawning period extending from early January to early June. All the females over 34.4 cm in body length are mature. The peak value of gonadosomatic index (GSI) was attained in January and continued to May and thereafter decreased gradually from June to August. The analysis of ova diameter revealed that there are eight ova groups in each ripe and spawning ovary; the first four
groups are small and transparent and the remaining four groups are yolky. Fecundity shows a wide range for a given length, the absolute fecundity has a linear relationship with length groups and gutted weight. Relative fecundity ranged from 743 to 1699 egg per 1 cm and varied from 92 to 148 eggs per 1 g. The general pattern of the histological development of the ovaries includes six periods: 1. Immaturation period characterized by “small spherical cells each with a large nucleus”. 2. The maturation period
characterized by “appearance of isolated follicular epithelial cells around the oocyte and the formation of yolk nuclei”. 3. Vacuolization period characterized by appearance of “marginal vacuoles; the oocyte
wall consists of zona radiata coated with a follicular epithelial layer”. 4. The yolk deposition period characterized by “the presence of yolk granules in the cytoplasm”. 5. Ripening period characterized by “migration of the nucleus to the animal pole”. 6. Spawning-spent period characterized by presence of “empty follicles, different stages of cytoplasmic growth”. The ultrastructure of the vacuolized and ripe oocyte wall showing the presence of five different layers, in which the outer most layers, is theca layer;
the second layer is the follicular epithelial layer and then the third and fourth layers are zona radiata externa and zona radiata interna, respectively. The fifth layer is known as “cortical alveoli".