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Diseases of Aquatic Organisms

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DAO 50:153-155 (2002)  -  doi:10.3354/dao050153

Cardiac abnormality with associated hernia in farmed rainbow trout Oncorhynchus mykiss

Trygve T. Poppe1,*, Renate Johansen2, Brit Tørud3

1Norwegian School of Veterinary Science, Institute of Morphology, Genetics and Aquatic Biology, PO Box 8146 Dep., 0033 Oslo, Norway
2National Veterinary Institute, Section of Fish Health, PO Box 8156 Dep., 0033 Oslo, Norway
3Veterinary Service in Aquaculture (VHHAS), 6681 Valsøyfjord, Norway

ABSTRACT: A new type of cardiac malformation in rainbow trout Oncorhynchus mykiss from a broodstock fish farm is described. The ventricle of affected fish was located dorsodextrally to the atrium, while the latter was saccular, grossly enlarged and protruded through the muscles of the ventral body wall, forming a hernia covered only by dermis and epidermis. Histopathological changes included hypoplasia of the outer compact layer of the ventricular myocardium and severe distension of trabecular structures within the ventricle and atrium. Affected fish tolerated stress very poorly, and the majority of the affected fish died during the freshwater period. The causation(s) are not known, but hereditary and environmental factors are likely, as no infectious agents were isolated or detected microscopically.

KEY WORDS: Oncorhynchus mykiss · Cardiac malformation · Hernia

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