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QTL mapping studies of growth traits based on high-density linkage maps in Northeast China has great significance for local enterprises in achieving MAS and improving the selection accuracy of parent fish. Here, we constructed a high-density genetic linkage map with 11,445 single nucleotide polymorphism (SNP) markers in a full-sib F1 family consisting of 120 progenies in Songpu mirror carp (Cyprinus carpio) reared in Northeast China. The consensus map covered 5471.93 centimorgans (cM) across the 50 linkage groups with an average resolution of 0.54 cM. Around the first overwintering period, a total of 15 QTLs for growth traits were identified on five LGs (LG7, LG8, LG14, LG30, and LG41). All of them were responsible for body weight (BW) at both 150 (before overwintering) and 350 (after overwintering) days, explaining 9.8–17.9 % of the phenotypic variation (PV). Two major-effect QTLs were detected on LG30, which explained 16.5 % and 16.4 % (qTL9–30), and 15.8 % and 17.9 % (qTL10–30) of the PV at 150 and 350 days, respectively. In addition, 15 loci were identified for 4 growth traits other than BW at both time points, including 6 loci for body length (BL), 7 loci for body height (BH), 3 loci for body thickness (BT) and 5 loci for head length (HL). These loci explained PV ranging from 15.9 % to 21.2 % for BL, 9.3–19.6 % for BH, 9.6–15.5 % for BT, and 10.6–18.1 % for HL. Nine candidate genes (IGF1b, LEPb, PACAP1a, GHSR1a, PPSS2, IRS1, APOAIb, IRS2band ADSS1) were identified, five of which were directly related to growth hormone (GH), including IGF1b, PACAP1a, GHSR1a, PPSS2and IRS1. Notably, three genes (GHSR1a, PPSS2and IRS1) were derived from two major-effect QTLs (qTL9–30 and qTL10–30). In conclusion, these novel findings may shed light on early selection of growth traits of common carp cultured in Northeast China and other relatively high-latitude regions.

Integrin α6(ITGα6) is involved in a variety of cellular physiological responses and plays an important role in the immune response. Currently, common carp is severely affected by the virus of Cyprinid herpesvirus 3 (CyHV-3) in aquaculture. Studies have shown that ITGα6is associated with herpesvirus infection. However, the role of ITGα6in the response to CyHV-3 virus infection is still unclear. In this paper, we cloned the ITGα6from common carp (CcITGα6) and studied its expression profile after infection with CyHV-3. Two transcripts of CcITGα6were cloned, named CcITGα6aand CcITGα6b. The full-length cDNA of the CcITGα6atranscript was 3867 bp, the ORF was 3273 bp, and 1090 amino acids were encoded. The full-length cDNA of the CcITGα6btranscript was 3368 bp, the ORF was 3189 bp, and 1062 amino acids were encoded. Two transcripts of CcITGα6 consist of four parts: the signal peptide, extracellular region, transmembrane region, and cytoplasmic region. The difference between the two CcITGα6 transcripts lies in the cytoplasmic region and no homologous sequence. Similarly, the secondary structure, glycosylation sites, and phosphorylation sites were different in the cytoplasmic region. Phylogenetic analysis showed that CcITGα6 was highly conserved and clustered with zebrafish ITGα6b. The two CcITGα6transcripts were constitutively expressed in ten sample tissues but displayed distinct expression patterns. The highest relative expression levels of the two transcripts of CcITGα6were observed in the head kidney, whereas the lowest was observed in the heart. The relative expression levels of the CcITGα6btranscript in the five tissues were significantly higher than the relative expression levels of the CcITGα6atranscript (p < 0.05), and they were significantly lower in the brain (p < 0.05). After CyHV-3 infection, the relative expression levels of two transcripts of CcITGα6were higher in the breeding strain than in the non-breeding strain and reached the highest at 48 h and the lowest at 144 h. However, the expression of CcITGα6bin the breeding strain was significantly higher than the expression of CcITGα6bin the non-breeding strain at all infection stages (p < 0.05). This result indicated that CcITGα6bmight play an important role in resistance to CyHV-3 in common carp, which provides a theoretical basis for the study of the CyHV-3 resistance mechanism of common carp and lays the foundation for guiding breeding.