Revealing Natural Hybridization between Hypophthalmichthys Molitrix And Hypophthalmichthys Nobilis In Original Place（Xiangjiang River of China）Through Morphological and Molecular Approaches

Abstract

This study investigates natural hybridization between Hypophthalmichthys molitrix and H. nobilis in the Xiangjiang River using morphological and molecular approaches, aiming to elucidate hybridization patterns and driving factors, and provide a scientific basis for fish germplasm conservation. Morphological analysis revealed that most traits of suspected hybrids were intermediate between the two species, with some showing transgressive variation or alignment with one parent. Principal component analysis indicated closer proximity to H. molitrix. Genome resequencing confirmed hybrids as intermediate, with equal genetic contributions from both parents. COI gene analysis identified H. molitrix as the maternal parent, as hybrids exclusively carried its mitochondrial DNA. The study suggests that natural hybridization is driven by incomplete reproductive isolation, overlapping spawning grounds, and habitat alterations due to hydraulic engineering, which exacerbate abundance imbalances between the species. Asymmetric hybridization may be linked to physicochemical factors affecting gamete affinity. This study provides the first domestic evidence of natural hybridization in the Xiangjiang River, with H. molitrix as the maternal parent, and offers new insights into fish hybridization theory. Recommendations include strengthening fishery monitoring, restoring spawning grounds, and protecting habitats to maintain ecosystem stability and biodiversity.

Keywords: Natural hybrids, Asymmetric hybridization, Genome resequencing, Mitochondrial COI gene