Construction Of Microsatellite Genetic Linkage Maps For Half-smooth Tongue Sole And Japanese Flounder

Half-smooth tongue sole (Cynoglossus semilaevis) and Japanese flounder(Paralichthys olivaceus) are important cultured marine fish species in China. They havebeen the most popular fish species together with barfin flounder (Verasper moseri),Spotted halibut (Verasper variegatus) and turbot (Scophthalmus maximus) in thenorthern China.Half-smooth tongue sole (Cynoglossus semilaevis) is a commercially valuableflatfish that is widely distributed in Chinese coastal waters. Due to its commercial value,easy domestication and natural resource depletion, half-smooth tongue sole has beenselected as a promising species for aquaculture. It has been one of the most popularmarine species used in aquaculture in China.Japanese flounder (Paralichthys olivaceus) is a marine fish which is economicallyimportant as a food, and has been widely cultured in Asian countries such as China,Japan and Korea. It is mostly distributed along the coast of China, where it has beencultured for approximately20years due to its favourable traits such a fast growth rate,good adaptability to temperature and disease resistance in a variety of cultivationconditions.Recently, the number of wild individuals of the fish species is little, and thefisheries resource is rather critical. Meanwhile, the deterioration of maricultureenvironment cause the frequency of fish diseases, which results in increasing andappreciable economic damage, and also has adverse effect on the healthy developmentof aquaculture. The traditional methods of genetic improvement of quantitative traitshave relied mainly on phenotype and pedigree information, which are easily influencedby environmental factors. It is generally accepted that marker-assisted selection (MAS)could accelerate genetic improvement in a relatively short period, especially when thetarget characteristics are disease-related and there is a sufficient amount of observed genetic variation in a given trait. A genetic map constructed from a populationsegregated for a trait of interest is required for QTL identification. Information ongenetic markers associated with QTL can be used in MAS breeding programs toidentify and select individuals carrying desired traits. The mainly research results are asfollows:High-density genetic linkage maps of half-smooth tongue sole were developedwith1023microsatellite markers and one SCAR marker. The parents and F1progeny(92individuals) were used as segregating populations. The female map was composedof845markers in21linkage groups, covering a total of1526.7cM, with an averageinterval1.89cM between markers. The male map consisted of818markers in21linkagegroups, spanning1584.0cM, with an average interval of2.03cM. The genome lengthof half-smooth tongue sole was estimated to be1608.4cM for the females and1671.5cM for the males. Based on estimations of the map lengths, the female and male mapscovered94.9and94.8%of the genome, respectively. The length of linkage group variedfrom38.7cM to101.1cM, and the markers on the linkage group varied from23to74.The integrated map was constructed by incorporating the homologous parental linkagegroups, resulting in21linkage groups with a total of1667.3cM. Genome coverage ofthe integrated linkage map was approximately95.6%. Furthermore,159sex-linked SSRmarkers were identified. Five sex-linked microsatellite markers were confirmed in theirassociation with sex in a large number of individuals selected from different families.These sex-linked markers were mapped on the female map LG1f with zerorecombination and a LOD of22.9. The present linkage map was sufficiently dense toprovide systematic genome searches to identify QTL, such as disease resistance, growthand sex-related traits, and is very useful for marker-assisted selection (MAS) breedingprograms for economically important traits in half-smooth tongue sole.Genetic linkage maps were constructed for the Japanese flounder (Paralichthysolivaceus). The10thpopulation with80individuals, crossed by6812E36as femaleparent and681383B as male parent were used in this experiment. A total of947microsatellite markers were polymorphic in the reference family. The female map wascomposed of829markers, covering a total of1597.3cM with an average interval2.39cM between markers. The male map consisted of672markers, spanning1608.1cMwith an average interval of2.56cM. The genome length of Japanese flounder was estimated to be1716.3cM for the females and1735.8cM for the males, and the coverageof93.1%for the female map was observed and92.6%for the male map. The length oflinkage group varied from34.9cM to86.4cM, and the markers on the linkage groupvaried from10to46. The integrated map consisted of841markers, spanning1733.8cMwith an average interval of2.22cM. Genome coverage of the integrated linkage mapwas approximately94.0%. The mean recombination at common intervals throughout thegenome revealed slight differences between sexes,1.1times higher in the male than inthe female.The present study reports two microsatellite genetic linkage maps for half-smoothtongue sole and Japanese flounder after the screening a large number of SSR markers,many of which are available in the public domain, as well as certain previouslyunpublished ones. The linkage maps were sufficiently dense to allow systematicgenome searches to identify QTL.