Comparison of the reproductive traits of male and female Soleoidei fishes in Japan

In this study, we examined the seasonal reproductive traits and inter-sex differences in the gonadosomatic index (GSI) of four Soleidae fish species in Japan to gain insights into the life history traits of Soleoidei fishes. We found that the sex ratio of one of these species was significantly skewed toward females, whereas the other three species showed no significant differences in the frequencies of males and females. For all species, the GSI values for mature males were between 0.5 and 1.5, which were notably lower than those of mature females (GSI: 7-15), and the weight of testes was approximately 10% that of female ovaries, after normalizing for body weight. The lower GSI values of male Soleidae fish may be indicative of an effective energy allocation mechanism within populations.