The preoptic area (POA) of the hypothalamus plays a central role in regulating social behavior and emotional responses. In Amatitlania nigrofasciata, a monogamous species with strong biparental care, the role of dopamine (DA) signaling in pair bonding remains underexplored. This study investigates Tyrosine Hydroxylase (TH) and Dopamine Receptor 2 (D2R) expression across A. nigrofasciata, Mchenga conophorus, and Danio rerio, species with differing social behaviors. We hypothesized that increased TH-positive neurons in the POA may be associated with monogamous behavior. Using in-situ hybridization, we mapped TH expression in neurogenic regions, specifically within the POA, by co-localizing it with Dlx2. RT-qPCR analysis revealed significant upregulation of TH and D2R in A. nigrofasciata, while no changes were observed in the other species. These findings indicate developmental heterochrony in TH expression and potential heterometry in the POA influencing monogamy, advancing our understanding of how early neural mechanisms shape complex social behaviors in vertebrates.