Dynamics of Gill Responses to a Natural Infection with Neoparamoeba perurans in Farmed Tasmanian Atlantic Salmon.

Simple Summary: This study focuses on how Tasmanian sea-farmed Atlantic salmon respond to a natural infection with a parasite that causes amoebic gill disease (AGD), a major health issue for salmon globally. The research aimed to understand the progression of the disease by examining the salmon's gills at different stages of the outbreak and evaluating their response to freshwater treatment. The study employed both macroscopic and microscopic examinations of gills, as well as molecular tools to measure the abundance of amoebae and the expression of specific genes that indicate inflammation. Key findings showed a strong correlation between different measures of gill health and significant differences between distinct stages of AGD. After treatment, a varied response among the fish was observed, indicating that management strategies need to account for individual genetic, environmental, and health factors. The expression patterns of some inflammation-related genes highlight their potential as biomarkers for early detection of gill damage in salmon aquaculture worldwide. The results of this research are important as they can help develop better ways to detect and manage this disease early, potentially reducing losses in salmon farming and ensuring the sustainability of this vital food resource. Gill health has become a significant global challenge for Atlantic salmon (Salmo salar) aquaculture, particularly during the marine phase of farming. The increasing prevalence of gill pathologies has been linked to rising seawater temperatures, underscoring the need to evaluate existing tools for monitoring gill health and to develop novel approaches for early detection. In this study, we investigated the gill responses of commercially farmed Atlantic salmon to natural infection with Neoparamoeba perurans during an outbreak of amoebic gill disease (AGD) in Tasmania. Our focus spanned the low AGD prevalence, high AGD prevalence, and post-freshwater treatment stages of the outbreak. Evaluations of gill tissue included assessments of the gross AGD score, histopathological score, abundance of N. perurans (measured by 18S rRNA gene expression), and expression levels of inflammation-related transcripts. We demonstrated a strong correlation between different measures of AGD-related gill pathology and significant differences between distinct stages of the N. perurans outbreak. Post-treatment, fish exhibited considerable variability in their responses to the freshwater bath, highlighting the necessity for personalized management strategies that consider genetic, environmental, and health status factors. The expression patterns of angiogenin-1 (ANG1) and complement C1q tumour necrosis factor-related protein 3-like (C1QTNF3) emphasize their potential as biomarkers for early detection of gill damage in salmon aquaculture worldwide. [ABSTRACT FROM AUTHOR]