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

psychrophilum among rainbow trout was also affected by the severity of ectoparasitic
monogenean infestations caused by Gyrodactylus derjavini (Busch et al. 2003).
Flavobacterium psychrophilum has been cultured from the water and from algae covering
rocks in rivers (Amita et al. 2000), but it is highly susceptible to osmotic changes
(Michel et al. 1999). The bacterium can be cultured from stream water for up to four
months, after which “starved” bacteria remained viable but non-culturable for as long as
nine months (Vatsos et al. 2003). The organism remained viable and culturable in
sterilized 15 o C fresh water after starvation for as long as 300 days, but the addition of
nutrient-soils increased bacterial survival in water microcosms (Madetoja et al. 2003).
Isolates of F. psychrophilum retain their virulence for relatively short periods (up to 8
months) without special provisions and for even longer periods when isolates are either
lyophilized or frozen at –80 o C (Michel and Garcia 2003).
Clinical Presentation and Pathology
In his original description of BCWD among fingerling rainbow trout, Davis (1946) found
that affected fish displayed a remarkable pathology that began as a whitish discoloration
along the peripheral margin of the adipose fin that progressed to eventually invest the
entire caudal peduncle. In most cases, the adipose fin and the integument covering the
dorsal area of the peduncle became necrotic, which revealed the underlying musculature.
In latter stages of disease, tissue and muscle degeneration progressed to such an extent