# Pathogenic Characterization and Host Immune Response to Vibrio harveyi in Diseased Seriola dumerili

## TL;DR

This study investigates how Vibrio harveyi causes disease in greater amberjack and how the fish's immune system responds, offering insights for better disease control in aquaculture.

## Contribution

The study identifies virulence genes in V. harveyi and reveals immune-related gene activity in infected greater amberjack.

## Key findings

- Vibrio harveyi strain Vh-2 causes high mortality and severe splenic damage in greater amberjack.
- 396 genes in infected fish spleens show altered activity, with many linked to immune and metabolic processes.
- Vh-2 is resistant to ampicillin but sensitive to ceftriaxone, florfenicol, and meropenem.

## Abstract

The greater amberjack (Seriola dumerili) is an important farmed fish that often becomes sick from harmful bacteria, causing serious losses in aquaculture. In this study, we examined a disease-causing bacterium taken from sick fish and confirmed that it can trigger illness in healthy fish. We also studied how the fish reacts after infection by looking at changes in gene activity in its immune tissues. The results show that many genes related to defense and inflammation become more active. These findings help us better understand how the fish fights infection and may support improved disease control in aquaculture.

The greater amberjack (Seriola dumerili) is an economically important marine species that is prone to bacterial infections, resulting in high mortality rates and substantial economic losses. In this study, a virulent bacterial strain, Vh-2, was isolated from diseased greater amberjack and identified as Vibrio harveyi. Experimental infections caused high mortality and severe splenic damage characterized by tissue necrosis, abnormal pigment deposition, cellular disintegration, and extensive immune cell infiltration. A virulence gene analysis revealed that Vh-2 harbored multiple virulence-associated genes such as toxR, toxS, vhpA, vhpB, vhhA, vhhB, luxR, and pap6. Antibiotic susceptibility testing demonstrated ampicillin resistance but sensitivity to ceftriaxone, florfenicol, and meropenem. Transcriptomic profiling of infected spleens identified 396 differentially expressed genes (DEGs) compared to the control group, of which 293 were upregulated and 103 were downregulated. A functional enrichment analysis indicated that these genes were primarily involved in cell cycle regulation, DNA repair, metabolic processes, and immune-related pathways. These findings enhance our understanding of V. harveyi pathogenesis and immune responses of S. dumerili and provide new insights into the prevention and control of V. harveyi infections in marine fish.