Controlled Artificial Reproduction in Mouth Brooding Tilapia with Human Chorionic Gonadotropin:
A protocol for induced breeding in mouth brooding tilapia for genetic improvement is discussed. Human chorionic gonadotropin (HCG) was suspended in calcium free Hanks' balanced salt solution (c-f HBSS), and injected into the back muscle of blue tilapia (Oreochromis aureus) females at the dose of 0.5, 1.0 or 1.5 IU g-1 female. Males were injected with the hormone at the dose of 1.5 IU g-1 male. Control females and males were injected with c-f HBSS only. Females were isolated individually and allowed to spawn naturally, but isolated males were stripped for sperm. Sperm was diluted 0, 1, 2, 3, 4, or 5x in c-f HBSS and stored in the refrigerator at 4oC for 4 days. Naturally spawned egg batches of an isolated, hormone-injected female were fertilized daily with stored sperm of hormone-injected males and incubated at 28± 2oC. Spawning time was significantly advanced and more consistent among hormone-injected females than controls, and the response increased with an increase in hormone concentration. Apparently, the hormone enhanced predictable and synchronous spawning. The hormone also increased sperm production significantly. Sperm production in both hormone-injected and control males decreased over sampling time. The c-f HBSS extended viability of eggs removed from the mouths of isolated females for 1 h, and generally improved sperm motility and fertility (capacity to fertilize eggs) during cold storage. For all dilutions, sperm quality dropped with storage time. Hatching success of eggs fertilized with low (1-3x) sperm dilutions was better than that achieved with high (>3x) sperm dilutions and undiluted sperm. The hormone induction protocol facilitated greater control over the collection of gametes and programming of controlled artificial reproduction.
Journal of the Ghana Science Association Vol. 10 (2) 2008: pp. 70-77