| dc.description.abstract | Yersinia ruckeri (Yersinia) is a gram-negative bacterium and a challenging pathogen in Recirculating Aquaculture Systems (RAS), causing Enteric Redmouth Disease (ERM) in fish, including Atlantic salmon, which can lead to significant economic losses. Among the wide range of disinfectant agents used in aquaculture, ozone and peracetic acid (PAA) have shown great potential for eliminating various pathogens, including Yersinia, through their oxidative effects. Studying the effects of PAA, ozone, and Yersinia at the molecular level in fish can provide a better understanding of the physiological processes involved and improve disease management strategies in aquaculture. The two core objectives of this project were, first, to analyze the gene expression levels of Atlantic salmon parr exposed to PAA and ozone, either alone or during Yersinia challenge, and second, to study the effect of Yersinia on the gene expression of the fish.
The experimental setup involved a total of nine RAS units, divided into three sets (N=3), each designated for a specific treatment. Timepoint 1 served as the untreated group, where fish were not exposed to any disinfectant or Yersinia. At sampling point 2, the RAS units were exposed to continuous ozone at a concentration of 300-350 mV and semi-continuous PAA at a concentration of 1 mg/L for eight days. After introducing Yersinia (serotype O1) to the RAS units, samples were taken at timepoints three and five, 24 hours and 21 days post-inoculation, respectively. Samples were collected from four tissues—gill, skin, spleen, and olfactory. RNA was extracted, followed by cDNA synthesis and quantitative real-time PCR (qPCR) to compare gene expression levels.
Yersinia gene expression was below the detection level of the assay in all tissues. The number of genes that underwent significant changes between different time points was highest in gill, followed by skin, which had more changes than spleen, while olfactory had the fewest changes. Overall, Yersinia primarily suppressed antioxidant genes in gill. Ozone caused significant changes in gene expression, especially in gill and olfactory tissues, mainly with long-term exposure along with Yersinia. In contrast, PAA, along with Yersinia, temporarily affected the spleen and activated immune and antimicrobial responses in the skin and olfactory tissues, highlighting the suppressive effect of ozone on the examined genes compared to PAA. | |
