Zhifeng Zhou

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.

Distant hybridization in fish serves to integrate the genetic material from two distinct, distantly related species. In this study, we successfully produced a new hybrid fish (BG) through the intergeneric hybridization of blunt snout bream (Megalobrama amblycephala, BSB, 2n = 48, ♀) and green tip culter (Culter dabryi, GTC, 2n = 48, ♂). The objective of this research was to characterize the genetic, morphological, reproductive, and nutritional features of the hybrid compared with its parents. The DNA content and chromosomal number analysis revealed that BG was a diploid hybrid fish with 48 chromosomes. Integrated analysis of 5S rDNA, mitochondrial DNA, and Sox9 gene sequences revealed that BG predominantly inherited its genetic traits from BSB. Notably, certain gene fragments (376 bp segment of 5S rDNA class II and 718 bp segment of BG Sox9-II) originated from the paternal GTC, demonstrating biparental genomic integration. The growth performance analysis revealed that BG exhibited enhanced growth, achieving a body weight significantly greater than that of BSB and 1.81-fold that of GTC (both p < 0.05). The reproductive analysis indicated that BG possessed bisexual fertility, with testicular histology revealing accelerated spermatogenesis relative to BSB. Additionally, the nutritional analysis of BG muscle revealed elevated levels of crude protein (18.13%) and umami amino acids (5.45%) compared to those in its parents. BG showed higher growth, bisexual fertility, and improved muscle nutritional composition. This hybrid represents a promising resource for cyprinid breeding and aquaculture diversification.