Sex ratio of Parapristipoma trilineatum on the pacific coast of Tokushima Prefecture

摘要

Sex ratio of Parapristipoma trilineatum were studied using 3,896 and 3,184 specimens collected by entrapping around Ishima and Mugi-oshima Islands on the Pacific coast of Tokushima Prefecture, respectively, between 1994 to 1997. Monthly variations of the 2-year-old sex ratio in 1996 and 1997 were not found. In the populations spawned from 1989 to 1996 around Ishima Island and from 1991 to 1996 around Mugi-oshima Island, the sex ratios of 1 to 3 years old were close to 1: 1 and that of more than 5 years old were no bias to one sex as a whole. From these findings, we recognized that the sex ratio of Parapristipoma trilineatum is 1: 1 and there is no bias in the survival ratio between female and male.