Polymorphism in lactate dehydrogenase of skeletal muscle associated with YY sex chromosomes in medaka (Oryzias latipes)

Reproductive performance of male and female phenotypes in three sex chromosomal genotypes(XX, XY, YY) in the killifish, Oryzias latipes

The present study investigates the juvenile and adult reproductive performance of Japanese killifish, Oryzias latipes, which were successfully sex-reversed by feeding them male or female sex hormones during the fry stage. Sexual maturation of these laboratory grown fish of three known genotypes (XX, SY, YY) occurred earliest in untreated genotypes, next in genotypes treated with male hormone (methyl testosterone) and female hormone (estrone), respectively. The delay in sexual maturation caused by early exogenous, sex-hormone treatment may represent a disturbance in the delicate neural-gonadal axis. However, the degree of response was also strongly influenced by the animal's sex chromosomal genotype. XX fish, normally phenotypic females, were affected more by the male hormone than by the female hormone. XY and YY fish, normally phenotypic males, were delayed more by the female hormone than by the male hormone. This specific sex hormone-sex genotype interaction also influenced adult reproductive performance (sperm or egg production). Differences in the metabolism of male and female sex hormones by the XX, XY, and YY fish are probably responsible for these interesting findings.