SEXUAL MATURITY, SPAWNING AND SEX-RATIO O F THE 2 FORMS OF FLATFISH, GENUS PLEURONICHTHYS, IN KIISUIDO CHANNEL WATERS OFF THE PACIFIC COASTOF CENTRAL JAPAN
K. Watanabe et al., SEXUAL MATURITY, SPAWNING AND SEX-RATIO O F THE 2 FORMS OF FLATFISH, GENUS PLEURONICHTHYS, IN KIISUIDO CHANNEL WATERS OFF THE PACIFIC COASTOF CENTRAL JAPAN, Nippon Suisan Gakkaishi, 62(1), 1996, pp. 17-22
Sexual maturity, spawning season and sex ratio in the two sibling spec
ies of flatfish, genus Pleuronichthys, Honmeita and Bakemeita were sur
veyed. Spawning season in the Honmeita was estimated to be from the mi
ddle of November to the beginning of January, while the Bakemeita was
estimated to be from the middle of January to the beginning of May. Th
e Existence of seasonal isolation in the spawning season between the t
wo forms was distinctive. However, there remained the possibility of r
eciprocal crossing between the two forms in January, because the perio
d in which mature males with fully matured testis were observed was mu
ch longer than the spawning season. In this report, the existence of a
nother reproductive isolation mechanism, such as geological isolation
of spawning ground, is suggested, considering the absence of heterozyg
ous variants of these two forms in isozyme analysis and the lack of co
mmon mtDNA haplotypes between the two forms. Differences in the sex ra
tio were also demonstrated between the two species. The sex ratio of H
onmeita and Bakemeita were 1.5 and 1.0 respectively.