Segment-specific immune responses and microbial dynamics in the gut of largemouth bass (Micropterus salmoides) following viral infection

In teleost fish, the gut is a critical mucosal organ responsible for both nutrient absorption and immune defense. While regional differences in nutrient absorption have been well characterized, the interplay between microbiota and immune function across different intestinal segments remains poorly understood. This study aimed to investigate segment-specific immune responses and microbiota dynamics following largemouth bass virus (LMBV) infection. Using transcriptomic analysis and 16S rRNA sequencing, we systematically characterized the immune responses and gut microbiota composition across the foregut, midgut, and hindgut. The results revealed that hindgut exhibited stronger antibacterial and anti-inflammatory responses, which were beneficial for maintenance of mucosal homeostasis and a more stable microbial community. In contrast, the foregut and midgut exhibited significant alterations in the abundance of metabolism-associated microorganisms. Collectively, our findings revealed distinct immune and microbial profiles across intestinal segments and highlighted their strong correlation. This study enhances our understanding of the interplay between intestinal immunity and microbiota in teleost fish and provides a theoretical foundation for exploring intestinal immune regulation strategies in aquaculture.