Fish Reproduction

june 10
Broodstock Managemenet

In hatchery operation, large number broodstocks are difficult to handle and require more fasilities. Horvath, et al. suggested some guidelines to broodstock management in hatchery:
1. Select healthy fish with good physical characteristics,
2. Feed administration with good quality food of the appropiate dietary composition,
3. Keep the broddstock at a low stocking density,
4. Identify the sex of the broodstock and keep separately if possible, because mixed stocks aren inclined to spawn naturally,
5. Replace unspawned broodstock because the broodstock should not only tolerate but actually respond positively to induced spawning,
6. Keep spawned fish separately from other broodstock and feed with protein-rich feed at 2-5% body weight per day, in order to promote recrudescence of eggs and sperms,
7. Produce natural feed by adding fertilizers regularly,
8. Select deep ponds for keeping broodstock and supply with adequate water, in order to ensure favourable water quality and to stimulate gonadal development,
9. Before each spawning season, add some trash fish into the feed, in order to promote gonadal development as well as recovery,
10. Stock new spawners with old spawners, for replacement of broodstock

Gonad Maturation

Sexual maturity of teleost depends on many reason. As an poikilothermic animal, temperature as an importance factor that affect sexual maturity. Under tropical condition, some fish become sexually mature within the first year, but others fish takes longer 2-4 years. Maturation of gonad is process where tiny incipient sex cell develop, together with accecory tissue, into large organ with mature sperm or eggs that can be spawn. Maturation may occur once in a fish’s life or many time a year, depending to species and condition. Gonadothopin (GtH) regulate the formation and maturation of gametes.
GtH I important in oocyte growth, induces the theca cells to produce testosterone (T) which is converted to 17b-estradiol (E2) in the granulosa cells. E2 travels to the liver and stimulates production of vitellogenin (Vg). Vg return and sequestered by ovary as yolk protein. GtH II important in maturation of gonad, induces the theca cells to produce 17a-progesteron (17P) which is converted to 17a,20b-dihydroxy-4-pregnen-3-one (17,20DHP) in granulosa cells.
In aquaculture, final maturation and ovulation are the stages of reproduction most commonly induced by hormonal therapy. Many species spawn immediately after ovulation as long as the needed environmental cues and social cues are present.

recapped from N.Sukumasavin


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