Diseases of wild and farmed Finfish

Some fish and shellfish diseases of particular significance in Scotland.

Flavo psychrophilum and other flavobacterial species

Flovabacterium psychrophilum is the causative agent of Rainbow trout fry syndrome (RTFS), also known as bacterial cold water disease BCWD, in salmonids.  The bacterium causes significant economic losses in aquaculture particularly in freshwater hatcheries where juvenile fish exhibit exopthalmia and haemorrhaging of the abdominal areas, popeye as well as frayed fins and tail rot.  

Although little is known about the infective process of F. psychrophilum, it has been suggested that genotypic and phenotypic variation within the bacterial outbreak population may play a role whereby cells with different traits and roles in the pathogenesis might be required to overcome the host defence systems and establish a systemic infection (Sundell at al 2013).  F. psychrophilum is ubiquitous in the aquatic environment, particularly in freshwater, and is especially virulent at temperatures below 12ºC and does not survive at temperatures over 25ºC.  With no effective treatment available and a heightened antibiotic resistance the disease is difficult to control. 


  • Bacteriological culture and biochemical testing
  • Histopathology
  • Molecular confirmation

Other members of the flavobacteriaceae family causing disease in fish include, Flavobacterium branchiophilum, the etiological agent of  Bacterial gill disease and  Flavobacterium columnare, the pathogen responsible for columnaris disease / saddleback disease. 

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