Sex change and steroid profiles in the protandrous anemonefish Amphiprion melanopus (Pomacentridae, Teleostei)

Plasma profiles of several gonadal steroids and cortisol were examined in a field population of the protandrous, sex-changing anemonefish Amphiprion melanopus to elucidate potential roles of these hormones in gonadal sex change. Sex change was experimentally induced in males by removal of their dominant female pair mates. These sex-changing males were captured and sampled at 5, 10, or 20 days after female removal. Unmanipulated males and females were also sampled. Males had higher plasma levels of 11-ketotestosterone (11-KT) than did females, but had lower levels of androstenedione (Ad), testosterone (T), and estradiol-17 beta (E2). The three androgens showed decreases from male levels at 10 days, then an increasing trend at 20 days after female removal. E2 levels exhibited no changes from male levels until 20 days, when a significant increase over male levels was observed. Mature females had higher levels of Ad, T, and E2 than the 20-day treatment group, indicating that these steroids continue to rise after Day 20. The results support hypothesized roles for androgens in male function and E2 in female function in A. melanopus. However, E2 increases lagged behind oogonial proliferation, arguing against an influence of this steroid in the initiation of female function. Cortisol levels did not differ between males and females, but exhibited an increase during sex change, peaking at 20 days.