Fish display a variety of behaviours associated with sexual reproduction and these can be disrupted by exposure to environmental estrogens such as ethinyl estradiol. In order to understand better the basis of mating behaviours we are characterising the transcriptome of the brain of guppy (Poecilia reticulata) and seeking associations between gene expression and behaviour. By identifying and characterizing genes that play central roles in behaviour we can then identify how that expression is disrupted by estrogenic exposure.