Hybridization and polyploidization are regarded as the major driving forces in plant speciation, diversification, and ecological adaptation. Our knowledge regarding the mechanisms of duplicated-gene regulation following genomic merging or doubling is primarily derived from plants and is sparse for vertebrates. We successfully obtained an F1 generation (including allodiploid hybrids and triploid hybrids) from female Megalobrama amblycephala Yih (BSB, 2n = 48) × male Xenocypri davidi Bleeker (YB, 2n = 48). The duplicated-gene expression patterns of the two types of hybrids were explored using RNA-Seq data. In total, 5.44 × 108 (69.32 GB) clean reads and 499,631 assembled unigenes were obtained from the testis transcriptomes. The sequence similarity analysis of 4265 orthologs revealed that the merged genomes were dominantly expressed in different ploidy hybrids. The differentially expressed genes in the two types of hybrids were asymmetric compared with those in both parents. Furthermore, the genome-wide expression level dominance (ELD) was biased toward the maternal BSB genome in both the allodiploid and triploid hybrids. In addition, the dosage-compensation mechanisms that reduced the triploid expression levels to the diploid state were determined in the triploid hybrids. Our results indicate that divergent genomes undergo strong interactions and domination in allopolyploid offspring. Genomic merger has a greater effect on the gene-expression patterns than genomic doubling. The various expression mechanisms (including maternal effect and dosage compensation) in different ploidy hybrids suggest that the initial genomic merger and doubling play important roles in polyploidy adaptation and evolution.

Tryptophan (Trp) has received increasing attention in the maintenance of intestinal function. In this study, improved triploid crucian carp (ITCC) fed diets containing 6.35 g kg⁻¹ Trp had higher average daily gain (ADG) and improved villus height (VH) and crypt depth (CD) in the intestine compared to the control group. To elucidate the potential mechanisms, we used RNA sequencing (RNA-seq) to investigate changes in the intestinal transcriptome and 16S rRNA gene sequencing to measure the intestinal microbiota in response to 6.35 g kg⁻¹ Trp feeding in ITCC. Dietary Trp altered intestinal gene expression involved in nutrient transport and metabolism. Differentially expressed transcripts (DETs) were highly enriched in key pathways containing protein digestion and absorption and the AMPK signaling pathway. 16S rRNA sequencing showed that 6.35 g kg⁻¹ Trp significantly increased the abundance of the genus Cetobacterium, and the Firmicutes/Bacteroidetes ratio at the phylum level (P < 0.05). In addition, bacterial richness indices (Simpson index) significantly increased (P < 0.05) community evenness in response to 6.35 g kg⁻¹ Trp. In conclusion, appropriate dietary Trp improves the growth performance, and influences the intestinal flora of ITCC. This study might be helpful to guide the supply of dietary exogenous Trp in ITCC breeding.

Culter alburnus (topmouth culter, TC) is extensively distributed in various rivers and lakes in China. As a widely adaptive fish species, they have significant economic value and special ecological roles. Intergeneric hybridization is a pivotal strategy for generating novel hybrid lineages and species. In a previous study, we obtained an improved bisexual hybrid culter, BTBTF₁, derived from the hybrid lineage of Megalobrama amblycephala (blunt snout bream, BSB, 2n = 48, ♀) × Culter alburnus (2n = 48, ♂). In this study, we established an improved hybrid culter lineage by the self-crossing of BTBTF₁ and evaluated the biological characteristics regarding cytology, morphology, and genetics. DNA content and chromosome analyses confirmed that BTBTF₁-F₂ was a diploid lineage (2n = 48), with morphological traits exhibiting intermediate values between parental species, except for significantly TC-biased full-length-to-body length (FL/BL) and body length-to-head length (BL/HL) ratios (p < 0.05). ITS sequencing analysis revealed that BTBTF₁-F₂ inherited ITS1 sequences from BSB and TC. The global methylation level in BTBTF₁-F₂ was substantially reduced compared to progenitors, characterized by elevated full and diminished hemimethylation states. Transcriptomic analysis identified 7877 differentially expressed genes (DEGs), displaying 9.05%/8.30% maternal (BSB)-dominant and 17.01%/18.95% paternal (TC)-dominant expression patterns in BTBTF₁ and F₂. Remarkable intergenerational similarity in phenotypic and molecular profiles, coupled with bidirectional inheritance of progenitor characteristics, confirmed BTBTF₁-F₂ as a genetically stable allodiploid lineage. Remarkably, methylation patterns, and DEG expression collectively demonstrated significant TC-oriented bias (p < 0.05). This study reports a novel stabilized allodiploid culter lineage after a comprehensive assessment at cytology, morphology, and genetic levels, and provides new insights into genetic bias in hybrid progeny.

Distant hybridization induces genomic instability in offspring, driving the occurrence of gene recombination and mutation. Analysis of the genomic genetic composition can be used to infer the genetic evolutionary relationships between species. Based on the improved diploid carp (IDC) and the improved diploid scattered mirror carp (IDMC) lineages derived from distant hybridization between female common carp and male blunt snout bream, this study analyzed the genetic variation in their mitochondrial genomes to investigate the impact of distant hybridization on mitochondrial DNA (mtDNA) structural variation. Analysis of complete mitochondrial genome sequence structure and composition revealed subtle structural divergence across generations in both the IDC and IDMC lineages. Analysis of the protein-coding gene sequence structure demonstrated mitochondrial genome structure instability in nascent hybrid diploid lineages. Yet, subsequent self-crossing significantly narrowed the range of structural variation within each lineage. Furthermore, analysis of the genetic variation in the mitochondrial genome sequence structure revealed that paternal base insertions occurred in both F₁ lineages, accompanied by mutations predominantly consistent with those in crucian carp. The results of this study also indicated that the strictness of the paternal mtDNA elimination mechanism varied significantly among polymorphic individuals across different generations of the hybrid lineages, reflecting the randomness of paternal leakage.

The genomes of newly formed natural or artificial polyploids may experience rapid gene loss and genome restructuring. In this study, we obtained tetraploid hybrids (4n=148, 4nJB) and triploid hybrids (3n=124, 3nJB) derived from the hybridization of two different subfamily species Carassius cuvieri (♀, 2n = 100, JCC) and Megalobrama amblycephala (♂, 2n = 48, BSB). Some significant morphological and physiological differences were detected in the polyploidy hybrids compared with their parents. To reveal the molecular traits of the polyploids, we compared the liver transcriptomes of 4nJB, 3nJB and their parents. The results indicated high proportion chimeric genes (31 > %) and mutated orthologous genes (17 > %) both in 4nJB and 3nJB. We classified 10 gene patterns within three categories in 4nJB and 3nJB orthologous gene, and characterized 30 randomly chosen genes using genomic DNA to confirm the chimera or mutant. Moreover, we mapped chimeric genes involved pathways and discussed that the phenotypic novelty of the hybrids may relate to some chimeric genes. For example, we found there is an intragenic insertion in the K+ channel kcnk5b , which may be related to the novel presence of the barbels in 4nJB. Our results indicated that the genomes of newly formed polyploids experienced rapid restructuring post-polyploidization, which may results in the phenotypic and phenotypic changes among the polyploidy hybrid offspring. The formation of the 4nJB and 3nJB provided new insights into the genotypic and phenotypic diversity of hybrid fish resulting from distant hybridization between subfamilies.

The hybrid golden pompano “Chenhai No. 1” (CH), generated through distant hybridization [(♀ Trachinotus ovatus × ♂ T. blochii) × ♂ T. ovatus], exhibits significantly enhanced growth performance compared to its parental T. ovatus (TO). To elucidate the molecular mechanisms underlying this rapid growth, we performed integrated transcriptomic and untargeted metabolomic profiling of muscle tissue. Transcriptomic analysis identified 3172 differentially expressed genes (DEGs), with weighted gene co-expression network analysis (WGCNA) highlighting the ‘darkorange2’ module as strongly associated with rapid growth. Key DEGs, including mapk8a, acacb, and pkmb, were upregulated and implicated in energy metabolism, glycolysis, and signal transduction. Metabolomic profiling detected 576 significantly altered metabolites, predominantly enriched in glycolysis, the tricarboxylic acid (TCA) cycle, amino acid metabolism, lipid biosynthesis, and mTOR signaling. Integrated analysis revealed coordinated alterations between core module genes and differential metabolites in interrelated pathways, including correlations between pfkpa/pfkma and glyceraldehyde-3-phosphate, acacb and phosphatidylcholine/phosphatidylethanolamine, and sesn2 and leucine. These findings suggest that the growth advantage of CH arises from the coordinated enhancement of energy metabolism, amino acid sensing, and lipid metabolic remodeling, establishing a synergistic transcription–metabolism regulatory network. This study provides multi-omics insights into the molecular basis of rapid growth in an economically important teleost fish.