The criteria of testicular maturity during the spawning season and maturity rates according to age are described for male red sea bream Pagrus major collected from the Chikuzenkai between April and June, 1984. The degree of maturity of the testis is categorized into four stages on the basis of the results of a histological survey. The testicular maturity rates in fish aged 2, 3, 4 and 5 years were shown to be 18.7, 64.4, 80.0 and 100%, respectively. The fork length at which 50% of the fish attained maturity ranged from 280 to 300 mm. The weight and gonadosomatic index (GSI) value of the mature testis tended to increase with age and size. It was indicated that the sex ratio of mature red sea bream in the Chikuzenkai is probably 1:1 and that both sexes have a similar size composition at maturity.
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