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Histopathological and electron microscopical observations on rainbow trout fry syndrome
  1. E. Rangdale, BSc, MSc, PhD1,
  2. R. H. Richards, MA(Cantab), VetMB, PhD1 and
  3. D. J. Alderman, BSc, PhD, CBiol, MIBiol2
  1. 1 Institute of Aquaculture, Stirling University, Stirling FK9 4LA
  2. 2 Centre for Environment, Fisheries and Aquaculture Science (CEFAS), The Nothe, Barrack Road, Weymouth DT4 8UB


Rainbow trout (Oncorhynchus mykiss) fry and fingerlings with clinical signs of rainbow trout fry syndrome, and rainbow trout (0.5 to 3.5 g) with experimentally induced infections with Flavobacterium psychrophilum, were examined histopathologically and electron microscopically. Severe hypertrophy of the spleen and cellular degeneration were consistently observed. Distinctive features of the disease were the loss of definition of the splenic border and its replacement by a loosely structured eosinophilic layer, fibrinous inflammation and intercellular oedema within the spleen, and the presence of numerous filamentous bacteria interspersed throughout the organ.

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