EFFECTS OF LHRH-A ON THE GROWTH AND GENE EXPRESSIONS OF THE GROWTH AXIS IN NILE TILAPIA OREOCHROMIS NILOTICUS

Regulations of synthesis and secretion of growth hormone (GH) in teleosts are based on the dual control of hypothalamic stimulators including gonadotropin-releasing hormone (GnRH), dopamine (DA), and growth hormone-releasing hormone (GHRH), and hypothalamic inhibitors including somatostatin (SS) and norepinephrine (NE). Gonadotropin-releasing hormone (GnRH) can stimulate the release of growth hormone (GH). LHRH-A is an analog of mammalian GnRH. Nile tilapia (Oreochromis niloticus), a freshwater fish with sexual dimorphism. The effects of LHRH-A on the growth and expressions of GH, GHR and IGF-I mRNA in Nile tilapia remain unclear. Two experiments, designated as long-term and short-term experiments, were carried out. In the long-term experiment, two hundreds Nile tilapias of similar body weight were randomly assigned to the control group (intraperitoneal injection with phosphate saline) and the LHRH-A group (intraperitoneal injection with LHRH-A, 0.01 μg/g body weight) and fed under the same conditions for 70 days. The absolute growth rates (AGR), specific growth rates (SGR), condition factor (CF) and hepatosomatic index (HSI) were obtained by measuring the body length, body weight and hepatic weight at different stages. AGRW and AGRL levels of LHRH-A-treated male and female increased by 15.95%, 14.82% and 5.06%, 25.36%, respectively, compared to control group (PSGRW and AGRL levels of LHRH-A-treated male increased by 11.52%, 1.21%, 39.06% and 3.94%, 1.08%, 10.00%, respectively, compared to the control group (PSGRW and AGRL levels of LHRH-A-treated female increased by 14.29%, 6.88%, 5.83% and 24.19%, 9.09%, 28.21%, respectively (PCF and HIS levels of the LHRH-A group were also significantly higher than those of the control group (PPPP<0.01). The results indicated that LHRH-A could increase the mRNA expressions of GH in pituitary and GHR and IGF-I in liver, and significantly promote growth of Nile tilapia. Moreover, our study suggested that large scale administration of some neruoendocrine factor in diet to accelerate the growth rate of cultured fish has promising potential.