The aim of this project is to develop a cost-effective in vitro assay of brown trout gonads to quantify the molecular and cellular effects of aromatase inhibitors (AIs). AIs are chemicals that affect reproduction through inhibiting the action of the aromatase enzyme that catalyses the final conversion of androgens into estrogens.To encompass the sensitive period of gonadal development, the gonads will be collected from immature males and females from each species. Primary endpoints for the assay will include the synthesis of sex steroids (testosterone, estradiol) to assess the function of the sex steroidogenic pathways,  histology to assess morphology and immunohistochemistry to assess cell proliferation