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Megalobrama amblycephalais susceptible to hypoxia, which results high mortality rates in aquaculture. A preliminary study on a new variety of M. amblycephalacalled "Pujiang No.2" (GS-01–002–2020) discovered that its tolerance to hypoxia was significantly improved compared with that of wild breed. The objective of this study was to identify the key genes responsible for the enhanced hypoxia tolerance of this new variety. Based on previous RNA sequencing results, the function of btr02(bloodthirsty-like tripartite motif [TRIM] 02 gene), a key gene for hypoxia tolerance, was explored using CRISPR/Cas9. The results demonstrated that the mutation rate of M. amblycephala btr02+/-was 39.38 %. The 5-month-old mutant was of the same size as normal individuals; however, its tolerance to hypoxia decreased substantially. Specifically, the LOEcritof knockout mutants increased significantly (P<0.01), and the activity of antioxidant enzymes and the number of erythrocytes decreased significantly (P<0.01) after hypoxia stress. Nevertheless, there was no significant difference in gill morphology between mutant and control groups after hypoxia. These results imply that the btr02gene of M. amblycephalainfluences the ability of fish to adapt to hypoxia by affecting the antioxidant stress processes and erythrocyte production.

This study was to investigate the variances in muscles nutritional value and flavor quality between diploid (DBSB) and triploid blunt snout bream (Megalobrama amblycephala) (TBSB) muscles. Under the same culture conditions, the crude protein level, total and essential amino acids, eicosapentaenoic acid (EPA, C20:5 n-3), docosahexaenoic acid (DHA, C22:6 n-3), total polyunsaturated fatty acids (PUFAs) in muscle of TBSB were significantly (p< 0.05) higher than those of DBSB. In addition, compared with DBSB, TBSB demonstrated significantly (p< 0.05) higher equivalent umami concentration (EUC), sweeter and umami free amino acid and inosine monophosphate (IMP) content, and significantly (p< 0.05) lower bitter free amino acid and hypoxanthine (Hx) content. Furthermore, the odor active compounds 3-methyl-1-butanol (sweet, flowery), 1-hexanol (fruity aroma), pentanal (sweet, wine), octanal (fruity, orange) and nonana (rose, citrus) in TBSB were significantly (p< 0.05) higher than in DBSB, whereas dimethyl sulfide (pungent, stinky) and trimethylamine (fishy) were significantly. Taken together, TBSB was superior in both nutritional and flavor quality, providing a novel insight for fish quality improvement through polyploidy technology.