Effects of High-Fat Diet on Intestinal Microbiota in Largemouth Bass (Micropterus salmoides) from a Segmental Perspective

Intestinal functional zonation and segment-specific microbiota responses to high-fat diet (HFD) are poorly understood in largemouth bass. In this study, a feeding experiment was conducted using 390 largemouth bass with an initial body weight of 10.87 ± 0.05 g. The impacts of HFDs on intestinal histomorphology and microbial communities across four intestinal segments, compared with a normal diet (ND), using 16S rRNA gene sequencing and histological analysis. The intestine was divided into four segments based on morphological features and length. Results showed that HFDs significantly decreased intestinal fold height and induced inflammatory lesions. Microbial genera exhibited distinct spatial distribution: Klebsiella was concentrated in segments 1 and 2, Cetobacterium in segment 4, and Acinetobacter was abundant in most segments. HFDs significantly increased opportunistic, potentially pathogenic taxa, including Acinetobacter and Plesiomonas, while reducing probiotics such as Paenibacillus and Bacillus. Segmented analysis detected more differential microbes and revealed potentially pathogenic taxa overlooked by whole-intestine analysis. These findings reveal segment-specific microbial distribution and HFD-induced intestinal dysbiosis in largemouth bass, providing a theoretical basis for intestinal functional zonation and the optimization of healthy aquaculture strategies.