Size-dependent resistance to amoebic gill disease in naive Atlantic salmon (Salmo salar)

Amoebic gill disease, caused by the protozoan ectoparasite Neoparamoeba perurans, remains a significant threat to commercial Atlantic salmon aquaculture operations worldwide. Anecdotal reports from commercial producers suggest that historically, smaller Atlantic salmon smolts are more susceptible to AGD than larger smolts. Cohorts of large (> 350 g) and small (< 200 g) Atlantic salmon smolts were exposed to 50 N. perurans trophozoites per litre in a tank-based challenge. By the end of the challenge, the large smolt cohort had significantly lower gill parasite burdens and reduced AGD-related pathology compared to the small smolt cohort. An RNAseq approach was employed using an illumina sequencing platform to compare large smolts (> 350 g) to small smolts (< 200 g) to investigate potential gene expression differences resulting in AGD resistance.