Abstract
Amoebic gill disease (AGD) is a parasitic disease caused by the amoeba Paramoeba perurans, which colonizes the gill tissues and causes distress for the host. AGD can cause high morbidity and mortalities in salmonid and non-salmonid fish species. To understand the genetic basis of AGD and improve health status of farmed A. salmon, a population of ~ 6,100 individuals belonging to 150 full-sib families was monitored for development of AGD in the sea of Ireland. The population was followed for two rounds of AGD infections, and fish were gill scored to identify severity of disease in first (N = 3,663) and the second (N = 3,511) infection with freshwater treatment after the first gill-scoring. A subset of this gill-scored population (N = 1,141) from 119 full-sib families were genotyped with 57,184 SNPs using custom-made Affymetrix SNP-chip. GWAS analyses were performed which resulted in five significantly associated SNP variants distributed over chromosome 1, 2 and 5. Three candidate genes; c4, tnxb and slc44a4 were found within QTL region of chromosome 2. The tnxb and c4 genes are known to be a part of innate immune system, and may play a role in resistance to AGD. The gain in prediction accuracy obtained by involving genomic information was 9–17% higher than using traditional pedigree information.
Highlights
Amoebic gill disease (AGD) is a parasitic disease caused by the amoeba Paramoeba perurans, which colonizes the gill tissues and causes distress for the host
The population used originated from Marine Harvest (MH) breeding nucleus in Ireland which was developed with a cross of parents mated in 1:2 male to female ratio
The difference in estimates could have been due to multiple reasons e.g. difference in adopted methodology for the estimations, population differences, infection types used as phenotype which might activate different immune responses, e.g. first infection should activate innate while subsequent later infection should be mainly pursued by acquired immune system, and/or the total number of markers used in this study perhaps could not explain the total genetic variance
Summary
Amoebic gill disease (AGD) is a parasitic disease caused by the amoeba Paramoeba perurans, which colonizes the gill tissues and causes distress for the host. Attachment of amoebae to the gill initiates a localized host cellular response, including hyperplasia and hypertrophy of the gill epithelium and lamellar fusion[5] This pathological condition can cause high production losses in multiple salmonid and non-salmonid fish species[3,4]. The existence and severity of disease at farmed facilities is evaluated by random sampling of fish (~10–15) and investigation and/or scoring of gills for pathological conditions caused by amoeba as described by Taylor et al.[7]. Amoebic gill disease has been a major problem over many years in farmed Atlantic salmon (Salmo salar) of Tasmania, and cleaning of amoeba from the gills requires freshwater treatments which costs ~10–20% of the total production cost[4]. AGD is a rising threat for Norwegian salmon with first documented occurrence in 200613, and since amoeba has been regularly reported every year on the southwest coast and further north[14] in Norway
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