| Turbot (Scophthalmus maximus L) is a high-nutrition and economic valued species,it is a native European marine fish, naturally inhabits the Baltic, Black, andMediterranean Seas, it was introduced into China in1992. Accompanied by certain keytechnological breakthroughs, especially artificial breeding, the turbot farming industrydeveloped rapidly, and it became one of the most abundant marine species in the seasoff the coast of North China. However, genetic breeding to improve important traits ofturbot, including growth, disease resistance, and systematic artificial breeding, did notreceive enough attention, the issue could be observed in the loss of genetic diversity,increased inbreeding, the appearance of albino turbot in culture stocks and theincreasing long time before turbot appearing in the marketplace. To develop asustainable and environmentally friendly turbot industry, new strategies and techniqueswere required to develop new turbot strains with increased disease resistance and fastergrowth.Selective breeding can adapt the animals to artificial conditions and improve traitsof economic interest. Within an aquaculture breeding program, growth rate and survivalare highly desirable economic traits, estimation of the genetic parameters for these twotraits, including their genetic correlation under standard commercial rearing conditions,is required for evaluating the potential to select for, and thus maximize, the response intotal yield. Turbot is a cold water species, the optimum growth temperature is between18～20℃. When the water temperature is higher than26℃, it may cause the fish stressresponse, resulting in the decreased of survival rate, growth rate and resistance todisease. The natural seawater temperature is often more than26℃during the summerin Northern China, it need to join the cold water from the underground deep well, alarge number of pumping caused the groundwater level dropped significantly and watershortage. In the present study, genetic parameters for early growth and survival rate of turbotwere analysed with family data built in2011, the efficiency of phenotypic valueselection and breeding value selection were compared, faster growth and high survivalrate families were selected.2400fishes form60families were exposed to two thermaltolerance challenges (chronic and acute thermal shock), assessed indicates and statisticalmodels were taken examples from the literatures about the upper thermal tolerance inrainbow trout and resistance to White Spot Syndrome Virus (WSSV) in Penaeusvannmei, genetic parameters for upper thermal tolerance in turbot were analysed, Thehigh heat resistance families were selected when two thermal tolerance challenges weretaken into account. The results were as the following:1. The number of individuals of40families on days50and80were collected, andthe survival rate of every family was calculated, the body weights were recorded.Genetic parameters of the growth and survival traits were analysed using a linear animalmodel and threshold sire-dam model, respectively. The results showed that survivalrates of40families range from65.80%～97.75%, heritabilities of body weight andsurvival rate were0.195±0.292and0.098±0.096, respectively, the correlationcoefficient of family breeding values was0.494.2. The efficiency of phenotypic value selection and breeding value selection werecompared using the body weight and survival rate data. Results indicate that, whetherfor family selection or individual selection for body weight, the efficiency of breedingvalue selection was higher than that of phenotypic selection. the efficiency of familybreeding value selection for survival rate was also higher than that of phenotypicselection. Considering the growth and survival traits,12fast growth and high survivalfamilies were screened out.3. A chronic thermal tolerance challenge was processed with chronic thermal shock(1℃/day before26℃and0.5℃/day after26℃), it stopped the shock when it was29℃, then maintained this temperature until the end of the experiment, the experimentstopped when all individual died. Upper thermal tolerance served as the index of Heatresistance. Variance components were estimated using animal models and the averageinformation restricted maximum likelihood method, heritabilities of body weight andupper thermal tolerance were0.268±0.408å'Œ0.027±0.066, respectively.4. A thermal tolerance challenge was processed with acute thermal shock(1℃/day), it stopped the shock when it is29℃, then maintained this temperature until the end ofthe experiment, the experiment did not stopped until21day. Variance components,common environmental coefficients and heritability of heat resistance were estimatedusing three different trait definitions(binary test-survival, longitudinal data and binarytest-day survival) and eight statistical models(linear model, threshold(probit and logit)model, linear model with censored observations, linear model ingroing censoredobservations, linear repeatability model and threshold(probit and logit) repeatabilitymodel). Heritabilities of all statistical models range from0.003±0.007~0.272±0.188,most values were low, only threshold (Probit and Logit) was medium heritability. Theresult from correlation coefficients of the families breeding value in each tank showedthat the linear repeatability model is the most suitable model. The rank correlationcoefficient of families breeding value of each model showed that statistical models havea higher consistency family sort when they were used to analyze the same traitdefinition.5. Whether for chronic thermal shock or acute thermal shock for upper thermaltolerance trait, the efficiency of family breeding value selection is higher than that ofphenotypic selection. Considering two different thermal shock,10high heat-resistancefamilies were screened outGenetic parameters of growth, survival and upper thermal tolerance traits injuvenile turbot were estimated, the efficiency of phenotypic value selection andbreeding value selection were compared, fast growth and high survival rate and heatresistance families were screened out, providing with family materials for cultivatingnew breed. |
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