Abstract

Currently, aquaculture production of rainbow trout (Oncorhynchus mykiss) is a multibillion dollar industry; nevertheless, the development of this sector has not been exempt from pitfalls related to the recurrent presence of pathogens of bacterial origin. This is the case of Yersinia ruckeri, the etiologic agent of the infectious pathology known as Enteric Red Mouth Disease (ERM), causing serious economic losses that can be as high as 30–70% of production. Although several studies have been performed regarding pathogen features and virulence factors, more information is needed about the host defense mechanism activation after infection. Given this perspective, this study aimed to evaluate rainbow trout’s short-term innate immune response against infection with Y. ruckeri. A series of factors linked to the innate immune response were evaluated, including determination of hematological parameters, oxidative stress biomarkers, and analysis of the expression of immune-related genes. Results showed a significant decrease in several hematological parameters (white blood cell count, hematocrit, neutrophils, monocytes, lymphocytes, and thrombocytes) and oxidative stress indicators (SOD) between the control and infected groups. In addition, there were significant differences in the level of gene expression between infected individuals and the control group. Most of these genes (il-1β, il-8, il-10, tnf-α1, tnf-α2, socs3, mmp-9, cath, hsp-70, saa, fer, pcb) were upregulated within the first 24 h following infection. Results from this study showed more insights into the short-term immune response of rainbow trout to infection with Y. ruckeri, which may be useful for the establishment of biomarkers that may be used for the early detection of ERM.

Highlights

  • Aquaculture production of rainbow trout (Oncorhynchus mykiss, Walbaum 1792) has become a modern multibillion dollar industry, which represents 1.6 % of worldwide aquaculture production (848.1 thousand tons in 2018) [1]

  • It highlights the recurrent presence of pathogens of bacterial origin, such as the case of Yersinia ruckeri, which is a Gram-negative rod with rounded ends

  • Due to the high incidence of Enteric Red Mouth Disease (ERM) in rainbow trout cultured in Portugal, the present study aims to gain new knowledge on thiensPhoorrttu-tgeraml, tihnenpatreesheonsttsdtuefdeynsaeimmsetcohagnaiisnmnsewagkainnoswt Yle.drgueckoenri tihnefeschtioornt-.term innate host 2. dReefseunlstes mechanisms against Y. ruckeri infection

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Summary

Introduction

Aquaculture production of rainbow trout (Oncorhynchus mykiss, Walbaum 1792) has become a modern multibillion dollar industry, which represents 1.6 % of worldwide aquaculture production (848.1 thousand tons in 2018) [1]. In Portugal, the introduction and cultivation of rainbow trout occurred in the early 1960s, on the banks of the Coura River, and during the last decade, the production has remained relatively stable, oscillating between 900–1000 tons per year [2]. The development of this sector has not been exempt from pitfalls related to the presence of pathogens. Among these, it highlights the recurrent presence of pathogens of bacterial origin, such as the case of Yersinia ruckeri, which is a Gram-negative rod with rounded ends. Biochemical tests of Y. ruckeri allow it to be distinguished from other Yersinia species [6], and PCR is the clinical diagnostic system that has guaranteed the most reliable and specific identification of Y. ruckeri in the shortest period of time [7,8]

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