New cells added to the preoptic area during sex change in the common clownfish Amphiprion ocellaris

•POA sex differences occur across vertebrates, regulating physiology and behavior.•How the POA changes in fish that change sex in adulthood is not known.•We find addition of newly proliferated cells as one mechanism of POA sex change.•Data are consistent with potential gonad-dependent and -independent mechanisms.•Results reinforce the uniqueness of the timecourse of sex change in anemonefish.