Evaluation of Hypoxia Tolerance and Cloning-Expression Analysis of Related Genes in Hybrid Fish Derived from Megalobrama amblycephala × Xenocypris davidi Bleeker

The diploid distant hybrid (2nBY) derived from female blunt snout bream (Megalobrama amblycephal, BSB) × male Bleeker’s yellow tail (Xenocypris davidi Bleeker, YT). To investigate the hypoxia tolerance and the regulatory mechanisms of hypoxia-inducible factor-1α/2α (hif-1α/2α) in 2nBY, BSB, and YT, experiments consisting of 24 h of hypoxia treatment (DO = 2.0 ± 0.1 mg/L) followed by 6 h of reoxygenation were conducted. The loss of equilibrium critical oxygen pressure (LOEcrit), gill tissue structure, and antioxidant indices, as well as the full-length sequences and expression of hif-1α/2α in 2nBY, BSB, and YT, were compared. The results showed that the LOEcrit value of 2nBY was significantly lower than that of BSB but higher than that of YT (p < 0.05). After hypoxia treatment, the changes in gill tissue structure and antioxidant indices of 2nBY were less obvious than those of BSB, and the recovery rate was faster after reoxygenation. Sequence analysis revealed high similarity of hif-1α/2α between YT and 2nBY. After hypoxia treatment, hif-1α/2α were upregulated in the liver but showed distinct gill expression among the three groups. Their gill expression differences may contribute to varied hypoxic tolerance. Distant hybridization between BSB and YT successfully generated hybrid offspring with enhanced hypoxia tolerance relative to BSB. These results provide theoretical and technical support for the breeding of a new hypoxia-tolerant germplasm resource of bream.