Induction of Gynogenetic Diploid Males and Presumption of Sex Determination Mechanisms in the Hirame Paralichthys olivaceus

Abstract

When gynogenetie diploids having the proportion of females of 97.1% were administered orally with 17a-methyltestosterone at the concentration of 1—10 ppm μg/g diet) from 29.1 mm to 113.7-115.0 mm in total length, almost all treated gynogenetic diploids became males. Genetic effects in sex determination mechanism were discussed using groups showing high and low value of the proportion of females in gynogenetic diploids. A high proportion of females (average 90.3%) were obtained in 12 out of 13 lots at matings between sex reversed gynogenetic females (phenotypically males) and normal females. These facts strongly suggest that the genetic sex determination mechanism in hirame is basically XX-XY type. On the other hand there were no groups having high proportion of females in the matings between males in gynogenetic diploids which had shown low proportion of females and normal females. This result may be explained by using naturally sex reversed hirame (XY) as female parents in inducing gynogenetic diploids. Effects of environmental factors on sex differentiation were suggested in present studies and remained as future problems. © 1991, The Japanese Society of Fisheries Science. All rights reserved.