Maturation and Sex Ratio of Three-line Grunt, Parapristipoma trilineatum along the Southwestern Coast of Kii Peninsula, Japan

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Maturation and sex ratios were examined in three-line grunt, <I>Parapristipoma tyilineatum</I>, occurring along the southwestern coast of Kii Peninsula, Japan. Monthly changes in gonad index (GI) demonstrated that the spawning season in this region, from April to July peaking in May and June, was slightly earlier than previously reported for other regions. GI values indicated that no females at age 1 year and all females over 2 years were mature, compared with some males at age 1 year and all males over 2 years. The sex ratio was female-biased in May and June, but male-biased in July, September and October. Because the female-biased sex ratio in May was represented by fish in the 200-239 mm fork-length class (mainly 2-3 years old) and that in June by the 200-219 mm fork-length class (mainly 2 years old), together with the fact that these samples were caught by angling and set net, there seemed to be a behavioral difference between the sexes (mainly in 2-3 year-old fish) during their spawning migration. Based on whole samples, the sex ratio was female-biased in the 190-219 mm fork-length class (and 2 year old fish) and male-biased in the greater than 300 mm fork-length class (and fish older than 7 years) .
日本水産増殖学会の論文