| Scophthalmus maximus also known as Turbot,which belongs to the genus Scophthalmidmus,is an important economic fish for mariculture in our country.Feed expenditure has always been the highest proportion of turbot breeding cost.With the increase of feed price in recent years,feed expenditure has increased accordingly,which has seriously affected the development of turbot breeding industry.Feed conversion efficiency is an important index of feed utilization efficiency and an important economic trait of Turbot.If genetic breeding can be carried out according to the feed conversion character,improve the feed conversion character of turbot and breed new varieties with high feed conversion,the breeding cost and profit of turbot can be effectively reduced,and the development of the industry can be promoted.In order to achieve this goal,genetic evaluation and screening of related molecular markers for feed conversion characters of Turbot were carried out in this study,providing reference for improving feed conversion characters of Turbot by genetic means.The main results of this study are as follows:1.Evaluation of genetic parameters of growth-related traits such as feed conversion of TurbotIn this study,421 juvenile turbot from 15 full sibling families were used to measure individual feed conversion and genetic evaluation of growth-related traits of turbot through a specially designed cage culture system.The results showed that the heritability of body mass was 0.30±0.14 among growth-related traits of Turbot,which belonged to medium heritability.The heritability of body length and feed conversion were 0.47±0.17 and 0.45±0.21,respectively,which belonged to high heritability.The correlations of genetic and phenotypic correlations between body mass and body length were 0.955±0.031 and 0.892±0.019,respectively.The correlations between feed conversion and body weight and length were 0.783±0.149 and 0.750±0.166,respectively,and phenotypic correlations were 0.370±0.078 and 0.292±0.090,respectively.It is concluded that the forage conversion characters of Turbot have high heritability and good breeding potential,and can be improved by individual selection.2.Screening of microsatellite molecular markers related to feed conversion of TurbotMolecular marker-assisted breeding(MAS)can effectively solve the problem of difficult to measure feed conversion traits,so the screening of molecular markers related to feed conversion of Turbot was carried out.Microsatellite markers are commonly used in molecular marker-assisted breeding of fish.In order to screen out microsatellite markers related to the feed conversion rate of turbot and improve breeding efficiency,300 juvenile turbot were used as experimental materials in this study,and individual feed conversion rate was measured by a specially designed cage culture system.Thirty samples with the highest and lowest feed conversion rates were selected as the high feed conversion rate group(group H)and the low feed conversion rate group(group L)by BSA analysis.40 pairs of microsatellite primers were used to amplify the mixed pools of DNA from groups H and L of Turbot.The genotypes of individual PCR products of the two groups were counted,and the loci with different alleles between the two pools were screened.Through further population verification and family verification,the correlation between microsatellite loci and feed conversion rate of Turbot was analyzed.The results showed that the allele of microsatellite site YSKr148 at 238 bp had a significant positive correlation with the feed conversion rate of Turbot(0.359).The positive group had a significantly higher feed conversion rate than the negative group in family verification.The microsatellite site could be used as a molecular marker.To help complete molecular marker-assisted breeding for improving feed conversion characters of Turbot.3.Screening of SNP molecular markers related to feed conversion of TurbotSingle nucleotide polymorphism(SNP)refers to only a few nucleotide differences between different alleles at the same site or only small insertions,deletions,etc.Compared with microsatellite markers,SNP markers have higher distribution density in the genome,have higher genetic stability,and are easier to genotyping and automated analysis.In order to screen out SNP markers related to feed conversion rate of Turbot,this study selected tail fin samples of 300 juvenile turbot with known feed conversion rate and conducted whole genome resequencing.Clean Reads were matched to the reference genome using the mem module of BWA software and the results were analyzed with Qualimap software.The Haplotypecaller module of GATK software was used for SNP detection.The number of SNP sites in the original detection results was 6 724 384.A total of 2 691,355 SNPS were detected in the filtered results.The Farm CPU model of GAPIT software was used for genome-wide association analysis of feed conversion traits in the study population.The results of GWAS showed that 10 SNP sites were significantly associated with feed conversion of Turbot.Are 6-16420739,6-6495550,12-13569009,11-24062351,12-3217099,13-16056972,13-6779641,21-9350009,7-2338434 and 8-13266833,respectively.These loci were distributed on chromosomes 6,7,8,11,12,13 and 21 of Turbot.A total of 15 candidate genes were found near these loci,which may be related to feed conversion traits of Turbot.This study provides a theoretical basis for the formulation of breeding strategies for forage conversion traits of Turbot,and provides molecular tools for marker-assisted breeding of forage conversion traits by screening out molecular markers related to feed conversion.The identification of functional genes that might be related to the characters provided the research direction for the molecular mechanism related to feed conversion traits of Turbot,and laid the foundation for breeding and improvement of Turbot with high feed conversion.This study provides a theoretical basis for the formulation of breeding strategies for forage conversion traits of Turbot,and provides molecular tools for marker-assisted breeding of forage conversion traits by screening out molecular markers related to feed conversion.The identification of functional genes that might be related to the characters provided the research direction for the molecular mechanism related to feed conversion traits of Turbot,and laid the foundation for breeding and improvement of Turbot with high feed conversion. |
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