抄録
Since 1972, the catch of flatfish in Suõ-Nada decreased dramatically, and the catch in 1984 was only 52% of that in 1972.
This paper presents the biological parameters for stock assessment for Japanese flounder in Suõ-Nada, that is, age and body length at sexual maturity, main spawning season, maturity rate by age, and evaluation of the degree of sexual maturity which were mainly based on the data from 1980 to 1985.
The combination of maturity factor [103×gonad weight(g)/body weight without internal organs(g)] and observation of gonads by the naked eye can be applied to expedient judgement of sexual maturity for a large number of specimens. Maturity factor and mean body length at 50% sexual maturity were 10.0 in both sexes and 13.5cm in females and 12.0cm in males, respectively.The peak of the spawning season was the middle of December. The mean maturity rate was as follows:at age 0, 1, 2, over 3 years, it was 20, 70, 90, 100% for females and 20, 95, 95, 100% for males.
