Neoparamoeba Page, 1987: light and electron microscopic observations on six strains of different origin

Although amoebic gill disease (AGD) has emerged as one of the most severe h ealth problems in the fish industry, proof of the identity of AGD agents fr om various localities is still missing. Six strains of amoebae designated u ntil recently as Paramoeba species (the agents of AGD) were studied in cult ures by light and electron microscopy. Although they were isolated from gil ls of different hosts (Dicentrarchus labrax and Scophthalmus maximus) and f rom distant localities, their morphology was identical. The strains differe d from Paramoeba eilhardi, the type species of the genus, in that they lack ed the boat-shaped microscales on the cell surface but could be safely iden tified as belonging to the genus Neoparamoeba Page, 1987. Transmission elec tron microscopy revealed the presence of a symbiotic organism, Perkinsiella amoebae Hollande, 1980, in all strains under study. The only difference am ong the strains examined was found in the size of trophozoites, which could be attributed to the different origins of the strains, but until more refi ned diagnostic methods are available, in addition to N. pemaquidensis, the closely related species N. aestuarina also has to be taken into considerati on as the agent of AGD.