| Turbot Scophthalmus maximus is a commercially valuable and tasty flatfish withhighest farming yield in northern China, it has been the main farmed species inmarine fish culture industry in northern China since2002. However, the sustainabledevelopment of turbot farming industry was constrained by more and more arisingproblems such as depletion of underground sea water, germplasm degeneration,ascended culture cost and disease etc. Thus, works on selective breeding should becarried out urgently to foster strains with superior traits especially with fast growthtraits and thermotolerant traits, and so on. In the present study, we aim at selectivebreeding of thermotolerant strains and its possible mechanism was investigated bystudying the expressions pattern of hsp70gene through temperature stimulation toembryos at different developmental stages. In addition, we obtained a thermotolerantstain of turbot by selecting high-temperature tolerant broodstocks, high temperaturetolerance of embryos and families culture under high temperature. Meanwhile, thesurvival rate, albino rate, malformation rate and growth related traits recorded fromdifferent families was compared and analyzed. Also, the growth traits of differentfamilies of turbot were studied.1. We constructed the basic reference breeding population of turbot byintroducing France strain, Danmark strain and Spanish strain combined with theChinese culture populations from Lai-zhou, Hai-yang and Ri-zhao. Thethermotolerant population was also selected. The morphological analysis showed thatthere was notable difference between France and Ri-zhao strain, Ri-zhao andHai-yang strains were similar in morphology, and Denmark strain has the best bodyheight, which was obviously different from the other strains. The basic referencebreeding population was suitable for selective breeding study. Using principalcomponents analysis, three principal components were constructed, the contribution rate from the first, second and third principal component was47.07%,28.10%and15.45%, respectively.2. Genetic diversity within and between6turbot broodstocks strains wereassessed by using14microsatellite loci. The results showed that the number of alleles(A) and effective alleles (Ne) ranged from3to8and1.07to5.54, respectively. Theobserved heterozygosity value (H0) and unbiased expected heterozygosity value (He)ranged from0.440to1.000and0.509to0.824, respectively. The order of the Hevalues for the6broodstocks strains was: Spanish<France<Lai-zhou<Hai-yang<Danmark<Ri-zhao based on the genetic analysis results. There was no significantdifference in genetic diversity of the6turbot broodstocks strains. Genetic diversitycoefficient (Fst) was0.11088, which indicated that there was moderate geneticdifferentiation among6broodstocks strains. Hardy-Weinberg equilibrium and geneticdeviation index (d) showed a reasonable difference within each broodstocks strain，which indicated that they were suitable for basic reference breeding populations.3. The thermotolarant ability of turbot embryos to heat stimulates notably variedat different development stages. Embryos at gastrula stage and cell division stagewere eligible to heat-harden treatment, whereas embryos at the organic forming stage,tail-bud stage and hatching stages were suitable for heat-harden treatment. Thesub-lethal temperature,50%mortality (LT50) temperature, lethal temperature forembryo, yolk-sac larvae (0days after hatching, dah), preflexion larvae (10dah),flexion larvae (25dah) and juveniles (50dah) of turbot which experienced2hheat-harden treatment were examined in this thesis. The order of thermotolerantability of such5developmental stages was:10dah＜embryo＜0dah＜25dah＜50dah,which showed a trend of gradual increase with development generally.10dah stagehave the most fragile response to heat treatment.4. The expressions pattern of hsp70mRNA of turbot larvae and juveniles whichexperienced2h heat treatment were determined using semi-quantitative real-time PCR.After the same temperature drop of the same developmental stage, expression level ofhsp70mRNA was highest at1h post heat treatment, then decreased sharply at24h,and rebounded slightly at48h. Based on the expression level of hsp70, the young fish expressed highest level of hsp70, followed by juveniles and larvae. The hightemperature could stimulate higher expression level of hsp70in turbot.5. A total of39individual parent turbot were selected by culturing the adult fishunder high temperature condition, then the thermotolerant spawner population wasconstructed. In order to test the mothed of sellection at embryo stage, short timeheat-harden treatment was used to compare the high temperature tolerance of embryosat five different development stages: cell division stage, gastrula stage, organicforming stage, tail-bud stage and hatching stage. The results showed that thedifference of high temperature tolerance between5embryo developmental stages wassignificant. Tolerance of heat stimulates of embryos at gastrula stage and cell divisionstage were weak than that of embryos at the other3stages. The rate of normal larvaewas declined with the elevated temperature and prolonged heat-harden time, andshowed a strong correlation. The three embryonic development stages which suitablefor heat shock operation were organic forming, tail-bud and hatching stage. A total of11thermotolerant spawner fish strains and18full-sub families were selected throughheat shock and high temperature culture test. They became important part of the corebreeding population of turbot.6. The difference of growth related traits among full-sib families was notable. Itshowed a remarkable consistency between the total weight growth of110dah and185dah youngfish. The survival rate of youngfish from different full-sub families wascontrasting, and it was low overall. The survival rate may be decided by the quality ofembryo and sperm to a large extent. There were9abnormal traits observed in culturedyoungfish. By the comparison between parent fish and family with abnormalmorphology, some obvious morphological deformation were observed: albino,abdominal deformity, spine curvature and low-jaw upward, all these deformationtraits may be associated with parent, but gill cover missed, eye transformation failure,apple-buttock and inversus metamorphosis may be not associated with parents.Significant difference of albino rates among half-sibs families were observed, whichmight be caused by maternal inheritance and ova quality. There were no significantdifferences in growth rates and body sharp between albino and normal juveniles in the present study. Additionally, a fast growing family and three high-body type familieswere selected as candidates for selective breeding program from all the F2families.7. The heritabilities of10growth related traits were estimated by intra-groupcorrelation of full-sibs of turbot. The heritability of110dah youngfish in total weight,total length, body length, head length, length of up-jaw, length between two eyes, totalheight, body height, caudal peduncle height and caudal peduncle length were0.219,0.461,0.366,0.341,0.717,0.669,0.317,0.207,0.511and0.216, respectively. Theheritability of185dah youngfish in total weight, total length, body length, head length,total height and body height were0.383,0.269,0.286,0.322,0.319and0.352,respectively. The difference was significant in components variance of full-sibs withinsires and dams. From components of variance of full-sibs within sires and dams wereprecise and unbiased for the quantitative character traits. The present study shows thatthe heritability in the traits of turbot is moderate. |
PDF Full Text Request