Multi-omics interrogation of herbivorous phenotype acquisition in hybrid culter under a 30% crude protein diet.

BACKGROUND: Herbivorous teleosts represent eco-efficient alternatives for sustainable aquaculture, yet the molecular drivers of herbivory in hybrid culter remain elusive. We investigated the hybrid culter (BTBT)-derived from Megalobrama amblycephala (blunt snout bream, BSB, ♀) and Culter alburnus (topmouth culter, TC, ♂)-exhibiting transitional herbivory. RESULTS: Morphometric analyses revealed BTBT pharyngeal dentition (formula 2.4.5-5.4.2) and intestinal coiling (IL/BL = 1.63) intermediate between parental phenotypes. After a 12-week 30% protein dietary intervention, digestive enzyme assays demonstrated BTBT's gut cellulase activity (76.02 U/g) mirrored herbivorous BSB (79.83 U/g; P > 0.05) and exceeded carnivorous TC (47.71 U/g; P < 0.05). The 16S rRNA profiling identified enrichment of cellulolytic Flavobacterium and elevated carbohydrate-metabolizing pathways in BTBT. Liver transcriptomics further revealed superior xenobiotic detoxification and glycolytic plasticity in herbivorous BTBT. Multi-omics correlation networks exposed synergistic host-microbiota interactions governing plant polysaccharide utilization and enteric homeostasis. Crucially, h6pd emerged as a nodal regulator, orchestrating NADPH-dependent glycolipid equilibrium, free radical scavenging, and xenobiotic metabolism. CONCLUSIONS: Our findings establish that herbivory in BTBT arises through tripartite adaptation: Digestive system structural adaptation, symbiotic microbiota-driven enzymology, and conserved regulatory genetics.