Sex Ratio, Spawning Period, and Sexual Group Maturity of the Largehead Hairtail Trichiurus japonicus (Teleostei: Trichiuridae) in Korean Waters

This study was performed to obtain information on the sex ratio, spawning period, and size at sexual maturity for fishery management of the largehead hairtail Trichiurus japonicus in Korean waters. The overall sex ratio (female, F; male, M) was 1:0.46 (n = 1274 females:589 males, 68.4% female) and as fish increased in length, the proportion of females increased. The oocyte development pattern was group-synchronous development, for which oocyte groups at different stages can be identified within the same ovary. The average gonadosomatic index (GSI) showed two peaks in June (3.03) and August (3.10) in females and in May (1.81) and September (2.24) in males. The median value of GSI showed two peaks in May (2.65F, 1.78M) and September (2.55F, 1.87M) for both females and males. As a result of analyzing the GSI and the monthly gonadal developmental stages, the main spawning season was estimated to be bi-annual (May–June and September–October). The anal length of fish at 50% sexual maturity was analyzed using a logistic regression model and was determined to be 16.38 cm (female) and 18.31 cm (male).