- Atlantic salmon, Salmo salar L., were exposed to different concentrations of Paramoeba sp. The lowest concentration which induced amoebic gill disease (AGD) was 230 Paramoeba sp. L-1 and the severity of infection increased with increasing concentration. The concentration of Paramoeba sp. positively correlated with the number of gill lesions (R2 > 0.7). This study provides evidence that Paramoeba sp. is the causative agent of AGD and describes an experimental model that enables the severity of the induced disease to be controlled.