Gill disease in marine farmed Atlantic salmon at four farms in Ireland.

A study of four marine salmon farms was undertaken in Ireland in 2008, with a focus on gill health and disease. All four farms suffered severe gill disease resulting in mortalities and, in some cases, failure to thrive. The aetiology of the gill pathologies in some cases was associated with small gelatinous zooplankton and bacteria, but also involved epitheliocystis and parasites such as marine costia (Ichthyobodo species) and amoebae (Neoparamoeba species). Treatments with oral broad-spectrum antibiotics and/or freshwater baths had equivocal benefits. There was a strong association of susceptibility to gill disease with one genetic strain of salmon.