Bacterial Coldwater Disease
Synonyms
- Rainbow Trout Fry Syndrome (RTFS)
- Bacterial fry anemia
- Low temperature disease
- Peduncle disease
- Saddleback
- Tail-rot
- Systemic myxobacteriosis
Bacterial Coldwater Disease (BCWD) is caused by Flavobacterium psychrophilum, also known as Flexibacter psychrophilus and Cytophaga psychrophila. There may be strain differences among isolates but their importance from a fish health management perspective has not been demonstrated. Because of problems with isolating
the causative agent, correctly diagnosing the disease and differentiating F. psychrophilum from other closely related and concurrent diseases, there is a lot of confusion and misinformation regarding BCWD.
Host range, distribution, and Occurrence
BCWD is a serious disease of all species of salmonid fish. It is also known to cause disease in carp, tench, chub, and eel. It is known only to infect fish in fresh water. The disease does not appear to be host specific and may infect many aquatic vertebrates. BCWD is particularly virulent at water temperatures below 12 C. (54 F.). However, untrue to its name, the disease is known to cause significant losses at temperatures up to 16 C. (61 F.)
BCWD was first described in 1946 as a disease of trout and salmon in the United States. Today it is found in many areas of the world including North America, Europe, Scandinavia, Japan, Southeast Asia, Australia and Chile.
BCWD infects all life stages of fish from gametes and eyed eggs through to broodstock. The disease is most acute in eggs, fry and fingerlings and tends to be more chronic in larger fish. Mortality typically begins within 5 to 10 days following infection and peaks 20 to 60 days later, depending on water temperature and fish age. The disease is known to recur, particularly following stress or handling; such as during smoltification, grading, sorting, transport, vaccination, marking, etc. Total cumulative mortality is typically 5% to 20% but mortality of up to 90% has been noted. BCWD is often observed to precede or occur in association with other diseases such as IPN, IHN and VHS virus. mortality is typically 5% to 20% but mortality of up to 90% has been noted. BCWD is often observed to precede or occur in association with other diseases such as IPN, IHN and VHS virus.