Lysolecithin Improves Lipid Metabolism and Gut Microbiota: An Integrated Transcriptome and Microbiome Analysis in Largemouth Bass (Micropterus salmoides) Fed Stearin-Based High-Lipid Diets

Background: Supplementing aquafeeds with emulsifiers can enhance lipid utilization, yet the physiological effects of lysolecithin, derived from enzymatic lecithin conversion, remain under-explored. Objectives: This study examined the effects of lysolecithin supplementation on hepatopancreatic transcriptome and gut microbiota in largemouth bass (Micropterus salmoides) fed stearin-based high-lipid diets. Methods: Two diets were formulated: a control containing 130 g kg−1 stearin fish oil (SO), and in the experimental diet (SL), 3.1 g kg−1 rapeseed oil was replaced with 3.1 g kg−1 lysolecithin oil. Each diet was fed to three replicate groups for 56 days. Hepatopancreas and distal intestine were sampled for transcriptome profiling, and gut microbiota were characterized at 28 and 56 days. Results: Lysolecithin supplementation resulted in 424 differentially expressed genes compared with the control (322 up- and 102 downregulated). KEGG enrichment indicated major effects on lipid metabolic processes, notably activation of the PI3K-AKT signaling pathway, enhanced adipocyte lipolysis, and modulation of adipocytokine signaling, suggesting improved insulin sensitivity and lipid mobilization. Histological analysis showed mild distal intestinal inflammation in the SO group. Gut microbiota composition shifted over time; lysolecithin increased the relative abundance of Cetobacterium and reduced potential opportunistic taxa compared with the control. Conclusions: Overall, dietary inclusion of lysolecithin improved lipid utilization in largemouth bass, likely by enhancing lipid metabolism and promoting beneficial gut microbial profiles. These findings support lysolecithin as a promising feed additive for optimizing high-lipid aquafeeds.