Genetic parameters of resistance to amoebic gill disease in two Norwegian Atlantic salmon populations

Abstract

Amoebic gill disease (AGD) is an increasing problem in Northern Europe and selective breeding has been shown as a good strategy to manage this disease in Tasmania. To explore the possibilities to perform selective breeding for AGD-resistance in Norwegian Atlantic salmon, two controlled challenge tests and one field (on-farm) test were performed with fish from two different breeding companies. For the field test, full-sibs of the same families from one of the controlled challenge tests were exposed to AGD naturally in a net-cage in the sea in Ireland. In all three experiments, two rounds of AGD infection were run, and all fish were assessed when the average gill score had progressed to an advanced threshold. Following assessment, all fish were bathed in freshwater. Heritability for resistance against both first and second AGD infection in the challenge tests and the field test ranged from 0.09 to 0.20. Estimated genetic correlation between gill score in the challenge test and field test resistance ranged from 0.02 to 0.34 and was not significantly different from 0. The genetic correlation between gill score in the first and second infection of the field test was 0.69 and ranged from 0.09 to 0.18 in the two challenge tests. These results indicate that AGD resistance in Norwegian Atlantic salmon can be improved by selective breeding. However, further work to optimize the controlled challenge test to better predict field test resistance is required.