Introduction: reproduction in fish, as in all vertebrates, is regulated by GnRH control on gonadotropic hormones (GTH) activity. However, the neuroendocrine factors that promote GnRH and GTH activity are unknown. In Nile tilapia (Oreochromis niloticus), sexual activity and the ability to reproduce depend on social rank only dominant males and females reproduce. Here, this characteristic of dominant fish allows us to compare brain and pituitary gene expression in animals that do and do not reproduce, aiming to reveal mechanisms that regulate reproduction. Methods: an extensive transcriptome analysis was performed, combining two sets of transcriptomes: a novel whole-brain and pituitary transcriptome of established dominant males identified by behavioral assays, together with a cell-specific transcriptome of LH and FSH cells. Results: in most dominant fish, as determined behaviorally, the gonadosomatic index (GSI) was higher than in subordinate fish, and the leading upregulated pituitary genes were those coding for GTHs. In the brain, various neuropeptide genes, including oxytocin, cholecystokinin, and MCH, were upregulated these may be related to reproductive status through effects on behavior and feeding. In a network analysis combining the two transcriptome sets, brain aromatase (cyp19a1b), which is specifically expressed in LH cells, is the most central gene with the highest number of connections. Conclusions: the close correlation between behavioral dominance and reproductive capacity in tilapia allows us to unravel novel genes that may partake in the regulation of the HPG axis, highlighting aromatase as an important factor in integrating the brain and pituitary factors that maintain a sexually active organism. Overall design: Brain and pituitary RNA-seq of dominanat reproducing vs subordinate non reproducing male tilapia