Abstract
Common carp is one of the oldest and most popular cultured freshwater fish species both globally and in China. In a previous study, we used a carp strain with a long breeding tradition in China, named Huanghe, to create a new fast-growing strain by selection for fast growth for 6 years. The growth performance at 8 months of age has been improved by 20.84%. To achieve this, we combined the best linear unbiased prediction with marker-assisted selection techniques. Recent progress in genome-wide association studies and genomic selection in livestock breeding inspired common carp breeders to consider genome-based breeding approaches. In this study, we developed a 2b-RAD sequence assay as a means of investigating the quantitative trait loci in common carp. A total of 4,953,017,786 clean reads were generated for 250 specimens (average reads/specimen = 19,812,071) with BsaXI Restriction Enzyme. From these, 56,663 SNPs were identified, covering 50 chromosomes and 3,377 scaffolds. Principal component analysis indicated that selection and control groups are relatively clearly distinct. Top 1% of Fst values was selected as the threshold signature of artificial selection. Among the 244 identified loci, genes associated with sex-related factors and nutritional metabolism (especially fat metabolism) were annotated. Eighteen QTL were associated with growth parameters. Body length at 3 months of age and body weight (both at 3 and 8 months) were controlled by polygenic effects, but body size (length, depth, width) at 8 months of age was controlled mainly by several loci with major effects. Importantly, a single shared QTL (IGF2 gene) partially controlled the body length, depth, and width. By merging the above results, we concluded that mainly the genes related to neural pathways, sex and fatty acid metabolism contributed to the improved growth performance of the new Huanghe carp strain. These findings are one of the first investigations into the potential use of genomic selection in the breeding of common carp. Moreover, our results show that combining the Fst, QTL mapping and CRISPR–Cas9 methods can be an effective way to identify important novel candidate molecular markers in economic breeding programs.
Highlights
Except for the body length gain, which was non-significantly higher in the control group, all measured growth performance indices were significantly higher (P < 0.05) in the selected group than in the control group (Table 1)
2b-restriction site–associated DNA (RAD) libraries were sequenced for 250 specimens (190 selected and 60 control), generating a total of 4,953,017,786
A combination of the two was proposed as a promising strategy for the implementation of genomic selection (GS) at acceptable costs, where a panel size of 384 markers could be recommended for the selection of candidates for pig breeding programs if at least one parent of selection candidates is genotyped at high-density (Wellmann et al, 2013)
Summary
With the development of high throughput genotyping technology, the cost of genome-wide genetic markers decreased sharply, facilitating genomic selection (GS) and prediction of complex, quantitative traits (Meuwissen et al, 2001) After the first large-scale implementation of GS in dairy cattle breeding (Schaeffer, 2006), this technique has been applied in other cultured species, such as pig (Knol et al, 2016), lupin (Yang et al, 2015), wheat (Charmet and Storlie, 2012), and Atlantic salmon (An et al, 2012; Correa et al, 2015; Tsai et al, 2015; Bangera et al, 2017). As a result of centuries-long breeding tradition, a strain of common carp named Huanghe is deeply rooted in Chinese culture, and remains popular among consumers for its cultural and historical relevance, its growth performance is objectively somewhat worse than that of other modern strains (Zhang et al, 2013). Using this strain as the base, recently we established a new fast-growing strain (Su et al, 2018), here provisionally named Xinlong strain. BLUP is widely used in fish breeding (Lind et al, 2012)
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