Flavobacterium psychrophilum, cause of ... - cop.eXtension.org

et al. 1997), but its morphology may be affected by conditions of culture (Kondo et al.
2001).
Figure 1. Microscopic photo showing Flavobacterium
psychrophilum in a wet mount at 1000X. Photograph by R.
A. Holt
The bacterium is refractile, does not form microcysts or fruiting bodies, but produces
bright yellow colonies not greater than 3 mm in diameter with thin spreading margins
(Figure 2) on specialized agar (Borg 1960; Pacha 1968). Additional phenotypic
characteristics are presented in Table 2.
Figure 2. Flavobacterium psychrophilum
colonies with thin spreading periphery on
Cytophaga Agar. Photograph by R. A. Holt.
Epizootics of BCWD commonly occur when water temperatures range between 4 -10 o C
(Borg 1960), but mortality generally abates as temperatures approach 15 - 18 o C (Rucker
et al. 1953; Holt et al. 1989; Santos et al. 1992). In recent years at some fish hatcheries in
the Pacific Northwest, this disease has been observed to persist and cause death at water