Cytophaga psychrophila (Order Cytophagales) infections of the cranium and anterior vertebrae in salmonid fishes were associated with ataxia, spiral swimming along the long axis of the fish, and death.The syndrome was observed in 2 to 10% of underyearling coho salmon Oncorhynchus kisutch, rainbow trout Salrno gairdned, and steelhead trout S. gairdneri at several private, state, and federal hatcheries in Washington and Oregon, USA.Affected f.ish did not recover and ultimately died.Histoloqcal examination of affected fish consistently revealed subacute to chronic periostitis, osteitis, meningitis, and ganglioneuritis.Inflammation and periosteal proliferation of the anterior vertebrae at the junction of the vertebral column with the cranium with extension into the cranial case was a consistent feature of the disease.The adjacent nervous tissue, particularly the medulla, was often compressed by the proliferative lesion and this may have caused the observed ataxia.Though bacteria were seldom observed in these lesions, C. psychrophila was isolated in culture from the cranial cavity of all affected fish that were tested.Epizootiological observations suggested that the bacterium is the etiologic agent of the disease because the spiral swimming behavior and lesions were only observed in populations which had recovered from acute C. psychrophila infections, known as 'cold-water disease' '
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Kent et al. (1989) studied this question.