REGULATION OF GROWTH AND REPRODUCTIVE GENES BY PITUITARY HORMONES IN MALE AND FEMALE MOZAMBIQUE TILAPIA Oreochromis mossambicus

Male tilapia grow faster than female tilapia, a characteristic that is widely employed in aquaculture production. Differences in the allocation of energy towards somatic growth and reproductive functions may underlie sex-specific growth rates.  Sexual dimorphism in tilapia is largely governed by the endocrine system, which, through the coordinated actions of horm ones, regulates a range of physiological processes including growth and reproduction. Secreted by the pituitary gland, growth hormone (GH) regulates growth and development both directly through growth hormone receptors (GHR) and indirectly through the stimulation of hepatic insulin-like growth factor (IGF).  Also secreted by the pituitary gland, gonadotropins regulate gonadal development through the stimulation of sex steroid hormones.  Our objective was to characterize the mechanisms associated with the endocrine control of growth and reproduction that may underlie sexual dimorphism.

To address this objective, we surgically removed the pituitary gland (hypophysectomy) of Mozambique tilapia and replaced GH and gonadotropins by intraperitoneal injections with ovine GH (oGH) and ovine luteinizing hormone (oLH).  We found that hypophysectomy decreases gonadosomatic index (GSI) by ten days in both males and females; combined injections of LH and GH restore GSI to control levels (Figure 1).  These results suggest that combined actions of GH and LH play a role in maintaining gonadal development in both male and female adult tilapia.  Additional analysis of hepatic and gonadal expression of GHR, IGFs, and sex steroid hormone receptors will further our understanding of the sexual differences in the endocrine control of hepatic expression of GH/IGF system genes in tilapia. [Supported by HATCH (#HAW02051-H), NOAA (#NA18OAR4170347), NIH (1R21DK111775-01) and NSF (IOS-1755016)].