Sexual differentiation in zebrafish is complex. Although zebrafish sex determination is primarily genetic, hormonal and environmental factors can influence sexual development. 17 alpha-methyltestosterone (MT), a synthetic androgen, induces female-to-male sex reversal in zebrafish. MT treatment is routinely used in aquaculture for production of all-male populations. However, the molecular mechanisms underlying 17 alpha-methyltestosterone induced gonad masculinisation in fish are poorly understood.In this study, we analysed gonad transcriptomes of zebrafish treated with 17 alpha-methyltestosterone during gonadal development (from 20 dpf to 40 dpf and 60 dpf) and compared them with testis and ovary transcriptomes of untreated zebrafish. These data improve our understanding of the role of androgens in teleost sex differentiation.