Physiology of Finfish and Shellfish (2+1)

3.1.11. Seasonal changes in the female reproductive organ

These complete in 5 phases or periods.

1. Resting period: Normally it occurs between Aug to Sept. The ovaries are small, thin, thread like, translucent, pale or dirty white in colour with reduced vascularization. At this phase ovary consists of several number of oogonia and oocytes in the stage of oocyte I and oocyte II.
2. Preparatory period: This occurs between Oct to Dec. At this phase ovary becomes slightly larger, thicker, opaque and yellowish in colour. There is an increase in the weight of ovary. At this stage oocyte II and oocyte IV are found maximum in number.
3. Maturing period: This period occurs between Jan to Mar. at this phase ovary increase in the volume and weight about 2/3 to 3/4^th of the body cavity. Vascularization increases and the blood capillaries become well developed. Immature oocytes are reduced in number and stage V oocytes make their appearance in large number. Stage VI and VII oocytes are also present in reduced numbers.
4. Spawning period: Normally it occurs between April to June. During this phase, the ovaries show a well marked increase in their volume and weight. Ovary become turgid and yellow in colour with a large number of translucent eggs. Ovarian wall is almost transparent. Ova may be extruded by applying a pressure on the abdomen.
5. Post spawning period: It is also known as spent phase. Normally it occurs between July to Aug. The ovaries are flaccid, shrunk and sac like reduced in volume with dull colour. The vascular supply in the ovary is highly reduced. The ovary shows atretic and discharged follicles along with stage I and II oocytes.