Zoological Studies

Vol. 50 No. 4, 2011

Development of Gonadal Tissue and Aromatase Function in the Protogynous Orange-Spotted Grouper Epinephelus coioides

Ya-Ju Tsai1, Mong-Fong Lee2, Chia-Yung Chen1, and Ching-Fong Chang1,3,*

1Department of Aquaculture, National Taiwan Ocean Univ., Keelung 202, Taiwan
2Department of Aquaculture, National Penghu Univ., Penghu 880, Taiwan
3Center of Excellence for Marine Bioenvironment and Biotechnology, National Taiwan Ocean Univ., Keelung 202, Taiwan

Ya-Ju Tsai, Mong-Fong Lee, Chia-Yung Chen, and Ching-Fong Chang (2011) The protogynous orange-spotted grouper Epinephelus coioides is a diandric type of hermaphrodite. We found that a paired gonad developed in a forked morphology at 1 mo of age, an ovarian cavity within the gonad was formed at 4 mo of age, and ovarian lamellae containing oogonia and primary oocytes proliferated at 6.5 mo of age. A single spermatogenic cyst (SSC) developed at the margin of the ovarian lamella containing primary oocytes and then various stages of spermatogenic cysts (VSCs) proliferated within the gonads of primary males. In contrast, an SSC was present at the margins of the ovarian lamellae containing vitellogenic oocytes and atretic oocytes of secondary males at 5.4 yr of age. Positive immunohistochemical expression of proliferating cell nuclear antigen was detected in nuclei of oogonia, cortical alveoli oocytes, vitellogenic oocytes, spermatogonia, and spermatocytes, while perinucleolar oocytes, spermatids, and spermatozoa were negatively stained. After administration of an aromatase inhibitor (AI) in juvenile fish for 2 mo, they changed sex into males. Adult fish fed diets containing the AI for 4 mo also changed sex into males. Abundant mature spermatogenic cysts became the main components within the testicular lamellae where single residual primary oocytes were scattered. Immunohistochemical signals of aromatase were present in somatic cells around the oogonia, cortical alveoli oocytes, vitellogenic oocytes, and spermatogenic cysts. The results suggest that aromatase (estrogen) plays an important role in sex differentiation and is also involved in sex change in the orange-spotted grouper.

Key words: Aromatase, Fish, Gonadal differentiation, Male development, Sex change.

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