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RAINBOW TROUT FRY SYNDROME (RTFS)

Definition

Disease caused by Flavobacterium psycrophylum, formerly known as Cytophaga psycrophyla or Flexibacter psycrophylum. Prevalent in Denmark, France, Germany, Spain and the UK, it also occurs in North America as well as in Chile and Tasmania. It is also known as Cold Water Disease, RTFS or visceral myxobacteriosis. It affects mainly juvenile rainbow trout (0.2 to 10 g weight). Infected fish stop feeding and show darkened skin while also having pale gills and often bilateral exophthalmia. Fish tend to concentrate at the water surface. Larger fry (over 5 g) exhibit lesions and show severe erosions of the tail fin. The disease can also be transmitted via egg surfaces (eggs of carrier fish). Although treatment is possible, high resistance against antibiotics has developed in several fish farms in Europe.

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