Physiology of Finfish and Shellfish (2+1)

3.1.7. Seasonal changes in testes

Seasonal changes are found to appear in teleost fishes at the time of breeding. The testicular cycle in bony fishes divide into 5 phase or periods.

1. Resting period: After spawning a rest period comes in between Aug to sept. This period is called quisant period or phase. In this period, the testes are thin and yellowish in colour and seminiferous tubules are small in size but filled with spermatogonia.
2. Preparatory period: This occurs between Oct to Dec. The morphological appearance is almost similar with resting period but in this phase volume of testes increases. In this phase spermatogonia starts to divide.
3. Maturing period: This period occurs between Jan to Mar. In this period volume and weight of the testes will increase. Testes are more vascular and opaque and spermatogenesis takes place. Spermatogonia reduce in number and numerous primary and secondary spermatocytes are formed. Interstitial leydig cells become very well developed.
4. Spawning period: Normally it occurs between April to June. During this phase, the testes increase in volume and weight. They are turgid and become pink colour. Milt oozes out on pressing the abdomen. The seminiferous tubules increase in diameter and are full with sperms and various stage of spermatogenesis takes place.
5. Post spawning period: It occurs between July to Aug. At this period testes will be flaccid due to excessive discharge of sperm. Weight of testes also reduces. Germ cells of this phase are present in the form of spermatogonia.