Effects of husbandry on prevalence of amoebic gill disease and performance of reared Atlantic salmon (Salmo salar L.)

Improved husbandry has been identified as an area that may alleviate amoebic gill disease (AGD) on Tasmanian salmon farms. We report results of three trials that aimed to reduce AGD prevalence and/or minimise losses associated with AGD. In the first trial, cages were rotated between different sites and data compared to stationary cages that remained on a reference site; this arrangement was repeated over two consecutive years. The second trial studied the effect of prophylactic freshwater bathing, while the third trial considered the effects of sea cage size. All trials evaluated the effect of treatment on AGD prevalence, fish biomass gain, and the percentage of mortalities. No significant reduction of AGD prevalence was detected in terms of Neoparamoeba presence on the gills as measured by the immuno-dot blot assay. However, fish from the rotated cages showed a significant longer period between freshwater baths (P=0.037), and the mean biomass in the rotated cages (P=0.038 in year 1 and P=0.041 in year 2), and the non-prophylactic bathed cages (P=0.048) was significantly higher at the end of the trials. The mortality rate was not affected by any of the treatments. The results of these trials suggest that impact of AGD on salmon industry can be offset by adjustment of husbandry methods. © 2004 Elsevier B.V. All rights reserved.