Juvenile bisexuality in the red sea bream,Pagrus major |
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Authors: | Michiya Matsuyama Ricardo Torres Lara Shuhei Matsuura |
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Institution: | 1. Department of Fisheries, Faculty of Agriculture, Kyushu University, 46-04, Hakozaki, Higashi-ku, 812, Fukuoka, Japan 2. CINVESTAV-IPN U. Merida, Apdo. Postal 73 Cordemex, C.P. 97310, Merida, Yucatan, Mexico
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Abstract: | The histology of the gonad of the red sea bream,Pagrus major, was examined in order to study the early gonadal development, sexual maturation and sex ratio in a natural population. A
total of 1,117 fish between the ages of 4 months and 8 years were examined. Gonads of 4-month-old fish were either sexually
undifferentiated with a central cavity, or ovarian in form. Gonads of 12- and 18-month-old fish were ovaries or bisexual gonads,
while those of 2-year-old fish were ovaries, bisexual gonads or testes. Fish aged between 3 and 8 years had ovaries or testes,
except for a few bisexual gonads found in 3- and 4-year-old fish. The chronological appearance of females, hermaphrodites
and males in that order, and histological evidence, suggested that the testis originates from the ovary via a bisexual gonad
in the juvenile stage. The sex ratio of females to males at the age of 2 years and over was about 1:1, suggesting that hermaphroditic
red sea bream appear in about 50% of the juvenile population. The sexual pattern in this species, therefore, is concluded
to be gonochorism with a bisexual juvenile stage. |
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Keywords: | Gonadal structure Sex ratio Gonochorism Bisexual gonad Juvenile bisexuality Sexual maturation Vitellogenesis Spermatogenesis |
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