Dietary BmKn2-7 Supplementation Modulates Intestinal Microbiota and Hepatopancreatic Responses and Enhances Resistance to Vibrio parahaemolyticus in Litopenaeus vannamei

Background: Global expansion of Litopenaeus vannamei aquaculture has intensified the reliance on antibiotics for disease control, raising concerns about hepatotoxicity, microbiota dysbiosis and antimicrobial resistance. Synthesized scorpion venom-derived antimicrobial peptide BmKn2-7 is a promising alternative, but its efficacy and mechanisms as a dietary additive in shrimp remain unclear. Methods: A 56-day feeding trial was conducted with six diets: a basal diet (FM), four diets supplemented with BmKn2-7 (0.8, 1.6, 2.4 and 3.2 mg/kg), and a florfenicol diet (FL, 3.2 mg/kg). Results: Growth performance was unaffected by any treatment. However, FL group significantly reduced condition factor and hepatosomatic index and markedly increased serum ALT and AST. The A2.4 diet increased whole-body crude lipid contents and significantly elevated serum ACP, AKP, HDL-C, and TG. 16S rRNA gene sequencing showed that intestinal microbial diversity indices were numerically highest in the A2.4 group, although pairwise differences were not statistically significant. A2.4 was also associated with reduced Vibrio abundance and enrichment of genera such as Acinetobacter, while FL induced pronounced community shifts. Hepatopancreatic transcriptomics and pathway analysis indicated that A2.4 was associated with shifts in amino acid, organic acid, and carbohydrate metabolism, together with enhanced endoplasmic reticulum protein processing, whereas FL was mainly associated with reduced V-ATPase-related proton transport. Key BmKn2-7 responsive genes were positively correlated with phosphatase activities and lipid parameters, and Hsp90b1 was negatively correlated with ALT and AST. Following V. parahaemolyticus challenge, A2.4 showed the lowest cumulative mortality, significantly outperforming FL and high-dose BmKn2-7. Conclusions: Dietary supplementation with BmKn2-7 at 2.4 mg/kg improves intestinal microbial homeostasis, metabolic and proteostatic functions, and resistance to V. parahaemolyticus. These findings support the further evaluation of BmKn2-7 as a potential feed additive for reducing antibiotic dependence in shrimp aquaculture.