Gonadal development and sex inversion in saddleback anemonefish Amphiprion polymnus Linnaeus (1758)

Gonadal development and sex inversion of saddleback anemonefish, Amphiprion polymnus were described. One-month juveniles had sexually undifferentiated gonads with primordial germ cells aggregated in groups, while two- to three-month juveniles displayed immature hermaphroditic gonads containing early developmental stages of both male and female germ cells, namely spermatogonia, primary spermatocytes, oogonia, and primary oocytes in chromatin-nucleolus stage. Spermatogenesis began at 4 months having testicular tissue comprising of spermatogenic cells in all developmental stages but ovarian cavity was first seen later at 5 months. The male region of ovotestis was peripheral, whereas the female region was more centrally located. There was no connective tissue between ovarian and testicular areas. Six-to 11-month fish had slightly larger ovotestes than those at previous age. Protandric sex inversion first occurred at 12 months. Sex change was characterized by degeneration of male germ cells, deposition of yellow-brown pigment and the formation of vitellogenic oocytes. Before spawning activity began, their gonads contained female germ cells in all stages with numerous vitellogenic oocytes, whereas functional males had both ovarian and testicular tissues. Most females of breeding pairs had mature oocytes in their gonads and began to spawn when their ages reached 14 months.