Influence of social stability on the sex determination process in false clown anemonefish (Amphiprion ocellaris)

ABSTRACT To evaluate the involvement of plasma cortisol in sex determination in hermaphrodite protandrous sex-changing fish, sexually immature false clown anemonefish (Amphiprion ocellaris) were kept in groups of 3 individuals for 360 days. Observations of time-course changes of diurnal behaviour and plasma concentrations of cortisol, oestradiol, and 11-ketotestosterone were evaluated. The social hierarchy of the experimental groups was assumed to become stable during the middle period of the experiment, but unstable at the beginning and at the end according to the increase or decrease in the frequencies of agonistic behaviours. The plasma concentration of cortisol increased as the social hierarchy became unstable and oestradiol showed the opposite trend to cortisol. These results suggest that in protandrous anemonefish sex determination induced by social interaction is mediated by cortisol. The stability of the social hierarchy is considered to be very important for the sex determination process.