Genetics for amoebic gill disease resistance in Atlantic salmon

Amoebic gill disease (AGD) in Atlantic salmon is caused by the marine amoeba Neoparamoeba perurans. The amoeba colonises gill tissue and causes loss of gill function, hypoxia, acidioses and ultimately a high mortality rate. In Australia, AGD has been documented for over 25 years, and is controlled through routine prophylactic freshwater baths. This increases the production costs by up to 20 % and adds considerable stress to the fish. In 2011 and 2012, AGD was the major cause of salmon mortality in Scotland and Ireland with up to 90 % mortality on the worst affected farms. In Norway, the parasite was first discovered in 2006 on four different locations with documented gill problems (Steinum et al. 2008). The worst of these locations suffered 80 % mortality, but additional infections with other agents cannot be excluded. The amoeba was detected again in 2012 after analysing samples from locations with high mortality. A test of 47 random farms from the west coast of Norway showed that about 30 % of the locations had the amoeba present, but the fish on most of them showed no clinical symptoms of AGD). In 2013 as well, AGD has been documented in Ireland and Scotland as well as in Norway.

Main objective:

Identify the best approach for increasing AGD-resistance in Atlantic salmon by selective breeding

Secondary objectives:

1. Estimate genetic parameters for AGD resistance in a controlled challenge test and in a field test.
2. Validate if the gill score/mortality in the challenge test gives a good prediction of gill score/mortality in the field.
3. Estimate the predictive ability for gill score/mortality of genomic and conventional breeding values and the possible predicted genetic gain
4. Identify genetic markers associated with AGD resistance
5. Characterise host transcriptomic responses in resistant and susceptible fish during AGD infection at the site of infection (gills)