Studies on sex-manipulation and production of cloned populations in hirame, Paralichthys olivaceus (Temminck et Schlegel)

Hirame (Paralichthys olivaceus) is an important cultured flatfish species in Japan, Korea and China. Because females grow faster, methods of feminized culture were developed. Sex ratios were examined in gynogenetic diploids and normal diploids and their progenies in order to clarify genetic sex-determination and enable its artificial manipulation. It was revealed that this species has male heterogametic sex-determination. However, sex-differentiation of genetic females (XX) seems to be so unstable that spontaneous sex-reversal to physiological males can be caused by exogenous factors, especially high water temperature. Manipulating techniques for physiological as well as genetic sex were established using sex-steroids and/or controlling rearing water temperature. Homozygous clones were produced by the combination of inducing mitotic gynogenetic diploids and meiotic gynogenetic diploids over two generations. More vigorous heterozygous clones were produced by hybridization between different clones. These appear to be good material for fish breeding and commercial fish culture. (C) 1999 Elsevier Science B.V. All rights reserved.