This study evaluated the effect of probiotics (Clostridium butyricum, Bacillus coagulans) and Chinese herb polysaccharides (Astragalus polysaccharides, APS) on growth performance, immunity, disease resistance, and intestinal microbiota of rainbow trout (Oncorhynchus mykiss). Specimens of O. mykiss (n = 360; 79.9 ± 2.2 g) were fed for 42 days with different diets containing a basal diet (control, C0), supplemented with 10⁹ CFU/kg of C. butyricum + 10⁹ CFU/kg of B. coagulans (E1) and 10⁹ CFU/kg of C. butyricum + 10⁹ CFU/kg of B. coagulans + 100 g/kg of APS (E2) as experimental diets. The results indicated that both E₁ and E₂ diets increased specific growth rate, reduced feed conversion ratio, and optimized muscle composition. Compared with the control treatment, after trout were fed with E₂ diet 42 days, activities of SOD, T‐AOC, and CAT increased significantly, while malondialdehyde content decreased significantly in the E1 treatment. After Aeromonas salmonicida challenge, cumulative mortality was 80%, 41%, and 29% in C0, E1 and E₂ treatments, respectively. The abundance of Bacillales, Actinomycetales, and Pseudomonadales increased in the fish intestine of E₂ treatment, while that of Rhodobacterales and Rhizobiales decreased. These data showed that C. butyricum + B. coagulans with APS improved growth performance, enhanced immunity and disease resistance, and modulated intestinal microbiota of O. mykiss.

This study investigated the impacts of white spot syndrome virus (WSSV) on the gut microbiota of Penaeus monodon through a comparative microbiota analysis of infected and healthy shrimp using 16S rDNA sequencing. The WSSV-infected shrimp exhibited characteristic white spots, reduced feeding activity, and behavioral lethargy preceding 100% mortality. The comparative microbiota analysis revealed a significantly diminished α-diversity in the infected specimens, marked by phylum-level dominance shifts from Proteobacteria (72.68%) and Firmicutes (11.27%) in the controls to Cyanobacteria (75.51%) and Proteobacteria (15.63%) in the WSSV-infected shrimp. An LEfSe analysis identified Arthrospira_PCC-7345 and Halochromatium as significantly enriched taxa during infection, contrasting with depleted populations of Ruegeria, Marivita, Bacillus, and seven other genera. The distinct dysbiosis pattern characterized by the pathogen-favored taxa proliferation and commensal species suppression demonstrates WSSV-associated microbiota restructuring, potentially contributing to disease progression in farmed P. monodon. These findings establish intestinal microbial biomarkers for early WSSV detection in aquaculture systems.

Mycobacterium marinum is an opportunistic pathogen prevalent in aquatic environments, causing significant morbidity in fish, including Coho salmon (Oncorhynchus kisutch), a species increasingly cultured in Chinese salmonid aquaculture. This study investigated the immune response of Coho salmon to M. marinum infection and the bacterial proliferation dynamics in the liver and kidney. Transcriptome analysis revealed 5028 differentially expressed genes (DEGs) in the kidney and 3419 DEGs in the liver at 6 weeks post-infection. Gene Ontology and KEGG enrichment analysis highlighted pathways such as cytokine–cytokine receptor interaction, metabolic pathways, and Toll-like receptor signaling in the kidney, while the DEGs in the liver were enriched in metabolic pathways, immune system processes, and stress and defense responses. The temporal expression profiling of 15 immune-related genes, including acute-phase proteins (serum amyloid A-5 and hepcidin), cytokines (TNF-α, IL-1β, IL-17A), chemokines (CXCL13 and CCL19), pattern recognition receptors (Toll-like receptor 13), and other immune-related genes, showed significant upregulation against M. marinum infection, with stronger responses in the liver. Furthermore, it was found that there was a progressive proliferation of M. marinum in the infected liver and kidney from approximately 2.5 log₁₀ cfu/g at week 2 to about 6 log₁₀ cfu/g by 6 weeks, with a significantly higher load in the liver. These findings provide critical insights into the immune mechanisms of Coho salmon against M. marinum and the pathogen’s tissue-specific proliferation, offering a foundation for developing targeted control strategies against M. marinum in aquaculture.

Nowadays, members of the genus Enterobacter have been documented as human and aquaculture pathogens. To date, no reports have described Enterobacter bugandensis infecting Hippocampus abdominalis. In the present study, an isolate of E. bugandensis, designated H4, was identified as a causative pathogen in cultured H. abdominalis following Koch’s postulate, and its virulence properties were further described. The isolate’s genome consisted of a single circular chromosome and harbored several virulence and resistance genes, including, but not limited to, csgG, acrB, hcp, gndA, galF, rpoS, fur, rcsB, and phoP involved in adherence, antimicrobial activity, effector delivery systems, immune modulation, and regulation, as well as baeR, blaACT-49, ramA, hns, ftsI, acrA, gyrA, fabI, crp, oqxB, parE, gyrB, phoP, rpoB, tuf, ptsI, and fosA2 functioning against aminoglycoside, cephamycin, disinfecting agent and antiseptic, fluoroquinolone, macrolide, peptide, and other antimicrobials. Additionally, the isolate exhibited multiple resistance to cephalosporins, penicillins, and tetracyclines and demonstrated a median lethal dose (LD₅₀) of 4.47 × 10⁵ CFU/mL in H. abdominalis. To our knowledge, this is the first study to describe E. bugandensis infecting H. abdominalis. These findings highlight the zoonotic potential of E. bugandensis and underscore the need for targeted health management in seahorse farming.