Hybridization-Driven Herbivorous Adaptation in Fish: Morphological, Digestive, Transcriptome, and Microbial Evidence...

Modifying the feeding habits of economically valuable carnivorous fish species towards omnivorous or herbivorous diets is of significant importance in aquaculture. In previous studies, we obtained a hybrid fish (BM) by crossing herbivorous female Megalobrama amblycephala (BSB) (♀) with carnivorous male Culter mongolicus (MC) (♂). Preliminary research indicated that BM exhibits herbivorous tendencies and rapid growth. To further evaluate the feeding characteristics and application potential of BM, this study systematically analyzed and compared BM with its parental groups, focusing on the structural traits of feeding organs, digestive enzyme activity, hepatic transcriptome, and gut microbiota features. The results demonstrate that BM possesses intermediate morphological traits in its feeding organs, with measurable ratios lying between those of BSB and MC and closer to BSB. In terms of intestinal morphology, BM also exhibits hybrid characteristics, showing greater similarity to BSB. Compared to BSB, BM exhibited significantly higher trypsin and lipase activities in both the intestine and liver (p < 0.05), although these levels remained lower than those in MC (p < 0.05) and were closer to BSB. The α-amylase activity in BM was significantly lower than in BSB (p < 0.05) but higher than in MC (p < 0.05). Regarding muscle composition, BM showed a significant increase in protein content compared to both parental lines BSB and MC (p < 0.05), while its crude fat content was significantly lower than that of the paternal line MC (p < 0.05), and showed no significant difference from the maternal line BSB. Transcriptome analysis revealed that differentially expressed genes in the liver of BM were significantly enriched in pathways related to nutrient intake and metabolism, including the MAPK signaling pathway, insulin signaling pathway, glycerophospholipid metabolism, adipocytokine signaling pathway, arginine and proline metabolism, and glycolysis/gluconeogenesis, all closely associated with feeding habits in fish. The analysis of gut microbiota showed greater similarity between BM and BSB. Overall, the findings demonstrate that BM is a high-quality hybrid fish with herbivorous tendencies and elevated muscle protein content, which highlights its considerable potential for reducing feed costs and promoting sustainable aquaculture. These results provide supporting data for the future promotion and utilization of BM.