Diuron and its biodegradation metabolites were recently reported to cause alterations in plasma steroid hormone concentrations with subsequent impacts on reproductive development in fish. Since steroid hormone biosynthesis is regulated through neurotransmission of the central nervous system (CNS), studies were conducted to determine whether neurotransmitters that control hormone biosynthesis could be affected after diuron and diuron metabolites treatment. As the same neurotransmitters and steroid hormones regulate behavioral outcomes, aggression was also evaluated in male Nile tilapia (Oreochromis niloticus). Male tilapias were exposed for 10 days to waterborne diuron and the metabolites 3,4-dichloroaniline (DCA), 3,4-dichlorophenyl-N-methylurea (DCPMU), at nominal concentrations of 100 ng L. In contrast to Diuron, DCA and DCPMU significantly diminished plasma testosterone concentrations (39.4% and 36.8%, respectively) and reduced dopamine levels in the brain (47.1% and 44.2%, respectively). In addition, concentrations of the stress steroid, cortisol were increased after DCA (71.0%) and DCPMU (57.8-%) exposure. A significant decrease in aggressive behavior was also observed in animals treated with the metabolites DCA (50.9%) and DCPMU (68.8%). These results indicate that biotransformation of diuron to active metabolites alter signaling pathways of the CNS which may impact androgen and the stress response as well as behavior necessary for social dominance, growth, and reproduction.

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