Amoebic gill disease (AGD) represents a substantial risk for the fish health in Norwegian seawater fish farms. Development of amoebic gill disease can be controlled at site level, given early detection and treatment, but it is not considered possible to achieve and maintain areas free from the pathogenic agent.
AGD was first detected in Tasmania in 1984. The disease has since appeared sporadically in other parts of the world, and since 2010 in the northeast Atlantic. In Norway AGD was first observed in 2006. Since then, there have been outbreaks each year since 2012.
Saltwater fish disease
The disease affects Atlantic salmon throughout the seawater phase, and in particular post-smolts during the first autumn in sea. In Norway, AGD has additionally been observed in farmed rainbow trout, ballan wrasse, broodstock and juveniles and in wild caught corkwing wrasse used as cleaner fish in farms producing salmonids. The amoeba is found in some wild fish in Hordaland, but this fish has not developed the disease.
Paramoeba perurans is present in Norwegian waters from Vest-Agder county to Møre og Romsdal county, where also gill disease has been diagnosed. In Norway AGD recorded along the coast of Vest-Agder of Sør-Trøndelag. Sporadic detections of amoeba Paramoeba peru have been made northward to Troms county.
If left untreated, AGD could cause substantial losses in Norwegian fish farming areas. However, the currently inadequate amount of available data makes it unfeasible to estimate the total potential for future losses for the whole industry.
High temperature and high salinity are major risk factors.
Need more knowledge about the amoeba
Knowledge on the infection reservoir and spreading dynamics is lacking. The amoeba is sporadically detected in wild fish, but the knowledge is too scarce to make any assessment of the significance.
Early detection and treatment
Early detection of the parasite is of importance. The longer the disease has progressed, the more difficult it is to implement effective treatments. The most effective known treatment against AGD is fresh water, but hydrogen peroxide is also reported to be useful. If left untreated, it is evident from experiences in Tasmania and Scotland that AGD has the potential to cause major losses.
Commissioned by NFSA
The Norwegian Food Safety Authority (NFSA) asked the Norwegian Scientific Committee for Food Safety (Vitenskapskomiteen for mattrygghet, VKM) for a risk assessment of amoebic gill disease (AGD). The NFSA has asked for this risk assessment to assess whether the disease should be listed on List 3 of Annex 1 of the Regulation 17 June 2008 no. 819 on the placing on the market of aquaculture animals and products thereof, and on the prevention and control of certain diseases in aquatic animals. To prepare scientific background documents necessary to answer the questions, the VKM, Panel on Animal Health and Welfare, established a project group consisting of both VKM members and external experts.