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

water or filtered and ultraviolet-irradiated or ozonated water supplies prior to ponding or
placement in production raceways.
Proper management of fish culture conditions, monitoring and maintenance of high
standards for water quality, and adequate sanitation procedures are other essential
requisites that may help to avoid and/or limit the severity of BCWD or RTFS epizootics.
Equipment may be disinfected in 1-2% formalin for 10 minutes, in 0.5-1% chlorine for 2
minutes, or by exposure to alkaline conditions equal to pH 13 for 2 minutes (Branson
1995). Stresses associated with high water velocities and heavy rearing densities may
elevate the level of mortality among cultured fishes and should be avoided (Wood 1974;
Sarti and Giorgettii 1996; Iguchi et al. 2003). Wood (1974) has recommended that water
flows in incubators should not exceed 4 - 5 gallons per minute and that the population of
each tray should be adjusted in order to avoid oxygen deficiencies at this rate of flow.
Substrates such as PVC netting material (Vexar) have been added to incubation trays to
reduce sac-fry movement and mechanical abrasion (Leon and Bonney 1979). This has
helped to reduce coagulated-yolk and BCWD losses in coho salmon fry. Other stresses
normally associated with routine fish culture practices (e.g.- handling during grading,
vaccination and transport, elevated rearing densities, poor water quality, and the presence
of other pathogens or parasites) may precipitate epizootics (Branson 1995; Evensen and
Lorenzen 1997). Nematollahi et al. (2003a) have demonstrated that adhesion of virulent
F. psychrophilum to gill arches of rainbow trout can be facilitated by high levels of
nitrites or organic materials in the water.