Sex change of hatchery produced Amphiprion ocellaris: Influence of mating system removal on gonad maturation and nesting success

Abstract

The influence of gonadal maturation and nesting success of the anemone fish Amphiprion ocellaris was analyzed through mating system removal. Four experiments viz., (i) Sex change of active male to female in the absence of active female, (ii) Juveniles in the presence of a functional male that was changing sex from male to female, (iii) Juvenile in the presence of a functional female, and (iv) Same length group juvenile fishes (total length: 50 mm) without the presence of adult fishes, were carried out. The gonad of male in experiment (i) showed first perceptible sign of sex inversion after 1 to 2 weeks. After 25 weeks the testicular zone almost disappeared and the gonad looked like maturing ovary with perivitellogenic oocytes and oocytes at various stages of development. The gonad of juveniles in the second experiment showed increased testicular development after 23 to 24 weeks, and testicular area became clearly discernible after 30 weeks. In the third experiment, the gonad of juvenile completed its spermatogenesis after 15 to 16 weeks and showed well-developed testicular zones. In the fourth experiment, the gonad of largest fish showed development of ovarian part after 24 weeks with oogonia and oocytes at various stages, and degeneration of testicular tissues. The observation of nesting success in the above experimental groups showed that spawning was obtained in the third group after 4 months of association; and after 12 to 18 months in the first and second groups, and after 20 to 24 months in the fourth group. The present study shows that in the absence or disappearance of adult female, the active male changes sex to female within a period of 25 weeks. The study also confirms that in the clownfish A. ocellaris, the largest and socially dominant fish in a host sea anemone (Heteractis magnifica) is generally female, whose gonads are functional ovaries with remnants of degenerated testicular tissues. The second largest fish in the same group is an active male and has gonad that are functioning testis but also possess non-functioning or latent ovarian cells (ovotestis). If the dominant female dies or is experimentally removed from the "queue", the male not only changes sex but also grows at an accelerated rate, and the juveniles also grow faster to become male and fill the size gap of the social group. This adaptation allows continuous reproduction. It is found that social structure plays an important role on the sex changing mechanism.