The Cultivation Of Broodstock And Selection Of The Families With High Growth Rate And The QTL Of Growth-related Traits In Half-smooth Tongue Sole(Cynoglossus Semiliaevis)

Half-smooth tongue sole is a specific and commercial ocean fish which iswelcomed by the vast number of consumers for its delicious taste and abundantnutritions. The market value is extremely high and the cultivation prospect is really good.In the last decade, half-smooth tongue sole farming developed rapidly and the annualoutput had reached tens of thousand tons, the annual value is more than30billion RMB.Half-smooth tongue sole has been one of the main marine cultured fishes.Now the factory farming of half-smooth tongue sole has been realized, thetechnology of artificial reproduction is getting mature, their reproduction is mainly relyon artificial spawning. For a variety of reasons, the mortality of the spawners is veryhigh after artificial spawning, and the quality of ovum is unsatisfactory. Addition, theextremely low growth rate of the female individuals limited the industry development ofhalf-smooth tongue sole, which made them can not growing to the commercial grade.Moreover, the percentage of female individuals is as high as60%⁷0%, which furtherlimited the breeding scale.In this paper, we have cultivated the broodstock of half-smooth tongue soleintensively with nereid. It turned out that the females grew rapidly and the date of gonaddevelopment had been brought forward, the egg laying period had been extended, theegg laying amount, fertilization rate, hatching rate, etc had risen notably, the mortalityrate had a significant reduction which was the most important. After4months’culturing,the average body weight of Group A rose from1.25kg to1.85kg, the net gain andaverage daily gain were0.6kg and4.92g/d respectively, which were higher than Group Bthat they were0.34kg and2.79g/d respectively. Before spawning, there were118individuals had matured, the mature rate was59.60%. However, only67individuals in Group B that the gonad had matured, the mature rate was33.84%. In Group A,11individuals were dead, the mortality rate was9.32%, by contrast, there were28individuals dead and the mortality rate was41.79%, which got much higher than32.47%over Group A. Gonad of parent fish of Group A began to develop on26th May, whichwas19days earlier than Group B, and began to spawn on10th September, which was6days early. The spawning season of Group A was24days,13days were extendedcomparing with Group B. Mean fecundity and mean floating eggs were411.3ml and263.2ml separately, which was60.6ml and71.2ml higher than Group B respectively,also the mean floating rate of Group A （80.97%） was notably higher than Group B（67.65%）. The fertilization rates of the2groups were60.37%and47.29%separately,Group A was13.08%higher than Group B. The hatching rates of the2groups were53.28%and22.40%, Group A was2.38times as much as Group B. Both of the2groups’aberration rates was low,2.36%and4.73%separately, however Group A was less thanhalf Group B. In this study, we cultured half-smooth tongue sole parent fish via usingfresh-living feeds, nereid for example, and the growth and spawning of parent fish havebeen studied detailedly that satisfactory experimental results were obtained. We initiallyfound that this method can reduce the mortality effectively, thus theories and technicalguidance have been provided for seeding.In this paper, we established22half-smooth tongue sole families （5neo-malefamilies were included） which were cultured in the same pond for the purpose ofcomparing their growth performance. This study shows that there are significantdifferences in growth rate. We selected2fast-growing families（16and61）whoseaverage daily gain were0.81g/d and0.56g/d;4faster-growing families（21,28,57and63）were selected, the average daily gain were range from0.48g/d to0.53g/d;12commonly-growing and4slow-growing families were selected also.3families（16,17and4） has a higher servial rate, which were73.0%,75.0%and65.5%respectively whichwas significantly higher than control（38.0%）. The growth rate of5neo-male families （3,4,7,20and56） were very slowly, it ranged from0.26g/d to0.38g/d, which were alllower than the control. It showed that fast growing families could be selected via familyselection, which could provide theories and new technical methods for the breeding andhigh quality seeding of half-smooth tongue sole.Additionally, we have made some reaserch on growth-ralated traits （body weightand total length） by QTL mapping.80F1individuals which were obtained by crossing the wild group with the cultured group were selected as the segregation population, andthe genetic linkage map of half-smooth tongue sole was constructed by suingmicrosatellite markers and mapping software Joinmap4.0.100SSR markers were usedto construct genetic linkage map, and50microsatellite markers were mapped to14linkage groups. Total length and body weight were mapped primarily, and then cobiningthe high density genetic linkage map the corresponding linkage group were mapped. Onthe basis of genetic linkage map, WinQTLCart2.5software was used to analysis thegrowth-related traits with composite interval mapping. Inorder to analysis themicrosatellite markers, LOD score2.5was selected as the threshold value for theregression analysis between traits and markers.Two QTLs that were identified for bodyweight, designated as We-1and We-2, accounted for26.39%and10.60%of thephenotypic variation. Two QTLs for body width, designated Wi-1and Wi-2, which weremapped in LG4f and accounted for14.33%and12.83%of the phenotypic variation,respectively.And2growth-related traits were obtained, Scaffold1442₅4298andScaffold080351.