Atlantic salmon cultured in commercial farms are at risk of contracting and transferring infectious bacterial diseases and other pathogens. Altering cage size aims to reduce prevalence of infectious diseases by reducing stress levels in fish and reducing contact time between fish in the same cage.
In 2000, a replicated study in Tasmania, Australia (Douglas- Helders et al., 2004) found higher levels of amoebic gill disease salmon, Salmo salar, stocked in 60m diameter round cages compared to those in 80m diameter cages. Levels of amoebic gill disease were 47% and 22%, respectively. Two cages with a diameter of 60m and three of 80m diameter were used for the study. Average biomass per pen was 2337 kg for the 60m cages and 2806 kg for the 80m cages. Monthly samples were taken from August to November. Signs of clinical disease were assessed using the routine Tasmanian salmon farmers gill assessment method.