A Gill Score Guide for AGD managament

April 4th, 2018

Amoebic gill disease (AGD) has been the main disease affecting farmed Atlantic salmon in Tasmania (Australia) since the mid-1980’s. The disease occurs year round and adds significantly to the cost of production because fish need to be regularly treated with fresh water throughout the marine growing cycle.AGD is proactively managed by regularly sub-sampling each caged population and inspecting the gills of anaesthetised fish for gross AGD signs (characteristic white mucoid spots and patches on the gill surface). This ‘Gill Score’ is a 0 (clear) to 5 (extensive lesions) scale and is assessed across all 16 hemibranch surfaces (i.e both sides of all 8 gill arches), it is a conservative scale that is designed to pick up and manage AGD from the onset of the disease. As gill score progresses, the risk to the fish increases from reduced feed intake, to increased stress and eventual death if not treated. Monitoring of the frequency of gill scores in a population and the average gill score (‘Gill Index’) over time allows the farmer to make informed stock management decisions to minimise adverse impact to the animals and to ensure that farm resources can be balanced to treatment requirements in a cost effective manner. A central concept of the gill score is that it is simple and consistent so that producers can compare AGD development trends between farms.

This booklet has been produced for the Atlantic salmon industry and fish health professionals in order to standardise AGD monitoring and communication.

Taylor et al. (2016) Gill Score Guide – Amoebic Gill Disease (AGD) management training document

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