Intestinal Microecology Dysbiosis, Cultivable Pathogen Composition, and Antimicrobial Susceptibility Profiles...

Intestinal exposure and ocular opacity occur in cultured hybrid porcupinefish, but the associated pathological lesions and gut microecological changes remain poorly characterized. Hybrid porcupinefish were assigned to a healthy control group (CT-CD-JK), an intestinal exposure group (CT-CD-FB), or an ocular opacity group (CT-YQ-FB). Gut microbiota, histopathology, cultivable bacteria, and antimicrobial susceptibility were assessed using 16S rRNA sequencing, hematoxylin and eosin (H&E) staining, bacterial isolation and identification, and disk diffusion testing. Diseased fish showed evident intestinal and ocular tissue injury. Microbial richness was reduced in the CT-CD-FB group, and gut microbial community structure differed among groups (permutational multivariate analysis of variance [PERMANOVA], R² = 0.5058, p = 0.001). At the phylum level, Firmicutes increased in the CT-CD-FB group, whereas Proteobacteria accounted for a higher proportion in the CT-CD-JK group. Linear discriminant analysis effect size (LEfSe) further indicated group-specific enrichment patterns. A total of 23 cultivable isolates were obtained, among which isolates assigned as putative Vibrio harveyi based on 16S rRNA sequence alignment accounted for 90.9% of isolates derived from intestinal contents in the CT-CD-FB group, which was higher than the 16.7% observed in the CT-CD-JK group. Antimicrobial susceptibility testing suggested a potential multidrug-resistance risk among the isolates; however, higher proportions of susceptible (S) isolates were observed for ceftriaxone (CTR), quinolones, aminoglycosides, and chloramphenicol (C). These preliminary findings suggest that gut dysbiosis, intestinal tissue injury, and a higher detection proportion of putative Vibrio harveyi were associated with intestinal exposure in this small cohort of naturally diseased hybrid porcupinefish, providing a basis for subsequent pathogen-verification studies and antimicrobial-susceptibility assessment.