occurrence of a motile aeromonas septicaemia in the imported ornamental fish, oscar (astronotus ocellatus): isolation, characterization and pathogenicity

a bacterial septicaemia occurred in 3-female oscars (astronotus ocellatus) of about 2-year old held in 300l freshwater aquaria in south tehran. the external signs of infected fish consisted of lethargy, anaemia, distension (clinical dropsy), exophthalmia and cataract. internally there was a large amount of red-ascitic fluid accumulated in the abdominal cavity with haemorrhages/ hyperaemia of internal organs, in particular, liver kidney, peritoneum as well as the presence of dark-brown dots on the surface of liver. kidney was enlarged and undergone liqufactive necrosis. the bacterio logical examination resulted in isolation of single and pure gram negative rod bacterium in which biochemical and physiological characters resembles of aeromonas veronii biovar sobria. experimentally, this isolate was relatively virulent to goldfish of 2-5g at 20-23c. more details of condition such as histopathological features and possible predisposing factors are given in the text.