Marker-assisted breeding of a lymphocystis disease-resistant Japanese flounder (Paralichthys olivaceus)

An allele of a microsatellite, Poli9-8TUF, has a dominant effect at a single major locus and is responsible for resistance to lymphocystis disease (LD-R) in Japanese flounder. We developed a new population of Japanese flounder produced by marker-assisted breeding using this allele. A female that originated from the KP-B inbred line with LD-R that was homozygous for the favorable allele (B-favorable) and a male from a commercial stock bred for higher growth rate and good body shape were selected as parents. A female was selected as the LD-R-bearing parent because the recombination rate of females is lower in the region where the LD-R locus is located. As expected, the B-favorable allele was transmitted as a heterozygote to the progeny (LD-R+ population). The LD-R+ population, when tested at two commercial fish farms that had LD outbreaks, showed no incidence of LD at either farm, while a control population without B-favorable alleles (LD-R−) had incidences of 4.5% and 6.3% at the two farms. These results show that marker-assisted breeding using molecular markers linked to an economically important trait is an efficient strategy for breeding.