A mortality level of about 16% occurred in two farmed rainbow trout of 1-3 g and 10-100 g in the north Iran during spring 1996. Infected fish were darkened in colour and showed fin and tail rot, gill necrosis with a general aneamia and ulceration of dorsal area at the base of dorsal fin. In some cases, the infected fish showed exophthalmia, flashimg swimming, and skeletal deformity including lordosis and scoliosis.
Bacteriological examinations of the lesions resulted in isolation of a Cytophaga/Flexibacter like bacterium (CFLB) when cultured onto a selective Cytophaga agar. Histopathologically, the epithelial layers of epiderm were lost and where the epithelial cells existed there were clusters of thin filamentous rod organisms invaded to epithelial tissue.
The epizootiological study of this condition shows that unsuitable long transportation, poor water quality, long exposure to the sunlight and malnutrition, in particular, vitamin deficiency were probably the main predisposing factors involved in the occurring of CFLB infection.This is first finding of CFLB infection reported in Iranian cold-water fish farm.