Morphological and physiological studies on sex differentiation and sex change in coral reef fish
2006
Nakamura, M.(Ryukyu Univ., Nishihara, Okinawa (Japan)) | Kobayashi, Y. | Miura, S.
In addition to gonochorism, several types of hermaphroditism are seen in fish. Individuals of some fishes bear gonads containing both mature ovary and mature testis. Some fishes change sex from male to female (protandrous sex change), others change from female to male (protogynous sex change), and a few can change sex either way and multiple times (bothway sex change). In many cases, sex change is cued by social factors, such as the disappearance of a male or female from a group. These phenomena reveal that the mechanisms of sex determination and sex differentiation in fishes, in being diverse and more plastic, differ from those of other higher vertebrates. First, our research focuses on analyzing the mechanism of sex differentiation in gonochoristic fish, using genetically controlled all-female and all-male tilapia Oreochromis niloticus. Second, we examined the sex change from an endocrinologic viewpoint, using morphological, physiological, and molecular techniques. In order to further characterize protandrous, protogynous, and bothway sex changes, we carry out experimental studies with the sea anemone fish Amphiprion clarkii, the three spotted wrasse Halichoeres trimaculatus and the honeycomb grouper Epinephelus merra, and the gobiid fish Trimma okinawae, respectively.
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