Analysis of high-fat diet tolerance in hybrid culter based on digestive enzymes, gut microbiota, and liver transcriptome

Hybrid culter (Derived from lineage of Megalobrama amblycephala ♀ × Culter alburnus ♂; denoted as BTBT) is a superior cost-effective aquaculture germplasm with pronounced high-fat diet (HFD) tolerance. A 12-week feeding trial using five crude lipid gradients (3–15%) demonstrated that a dietary crude lipid content level of 9–12% was optimal for BTBT and that BTBT had significantly lower HFD mortality than its parents. We analyzed the growth performance, liver histology, digestive physiology, gut microbiota, and liver transcriptomics of BTBT individuals to elucidate the mechanism of tolerance. Growth indicators and frozen liver sections revealed that BTBT had superior growth tolerance and better liver health than its parents under HFD conditions. Notably, BTBT exhibited attenuated lipase activity, thereby mitigating HFD-induced metabolic stress. 16S rRNA sequencing revealed that under HFD conditions, BTBT maintained moderate and stable gut microbiota diversity compared with BSB, and presented significantly higher PD whole tree, Chao1 and ACE indices than TC. Liver transcriptomic profiling using the short-time-series expression miner demonstrated enhanced mitochondrial function and transcriptional regulation as dietary lipid levels increased. Weighted gene coexpression network analysis identified intermediate inheritance modules enriched for lipid/energy metabolism, antioxidant defense, immunoregulation, and tissue repair pathways (e.g., fasn , fatty acid-binding protein 1b, ATP synthase F1 subunit alpha, gamma-glutamyltransferase 5b, BCL2-like 1, and heat shock protein 9). Furthermore, synthesizing the parental expression patterns formed a stabilized HFD-adaptive transcriptional network. In particular, Pearson correlation analysis revealed a significant negative association between Rhodobacter abundance, a BTBT-enriched genus, and liver expression of the proinflammatory gene elastase 2-like, thus suggesting a causal link to reduced inflammation. Collectively, these findings demonstrate that HFD tolerance in BTBT arises from the combined effects of enhanced nutrient absorption capacity, gut microbiota stability, comprehensive regulation of multi-pathway genes, and the anti-inflammatory effects of this signature genus.