Uso do hormônio HCG na reprodução natural de tilápias do Nilo (Oreochromis Niloticus)

Abstract

Synchronization of ovulation or spawning by hormonal protocols can allow for better reproductive management in a large diversity of domestic animals. Even though Nile tilapia reproduces naturally in captivity, seed production could benefit from the synchronization of spawning. Therefore, this study aimed to evaluate the effects of hormonal induction by hCG on the natural and artificial spawning of Nile tilapia. For this evaluation, two experiments were performed. In the first one, eighty young females (344 ± 90 g, close to 1 year old), forty old females (565 ± 152 g, close to 3 years old), and 75 males (527 ± 109 g, close to 1 year) were used. Young and old females were divided into two groups: (1) females induced with hCG at a dose of 3 IU · g-1 of live weight and (2) control females that received serum, both by the intracoelomic route. We evaluated three breeding cycles of 7 days long each, where each female received the injection just before being stocked with the males for natural reproduction in 5,000 L tanks (8 females: 5 males). After we obtained the results from the first experiment and intending to try to clarify doubts that arose, a second experiment was carried out. We evaluated different doses (0.5, 1.5, 2.5, and 3.5 IU · g-1 female), number of injections (1 or 2), and administration route (intracoelomic or intramuscular) of hCG hormone in 40 females for artificial reproduction by stripping. Our results indicate that the use of hCG hormone in a dose of 3 IU · g-1 of live weight is not effective for synchronization of natural reproduction in Nile tilapia and the negative effect of age on reproductive performance was not reversed by the use of this hormone. In the second assay, the reproductive performance was clearly higher in Nile tilapias that received one injection in comparison to those treated with two injections. There was no statistical difference between the administration routes evaluated (intracoelomic or intramuscular). The use of a single injection with lower doses of hCG (especially 0.5 and 1.5 IU · g-1 of female) resulted in 100% of spawned females in artificial reproduction and these doses should be investigated in future studies on the synchronization of natural spawning in Nile tilapia.