ARS | Publication request: Case report of an unusual heart abnormality in Rainbow trout (Oncorhynchus mykiss)

Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: March 7, 2011
Publication Date: March 28, 2011
Citation: Lafrentz, B.R., Lapatra, S.E., Heidel, J.R. 2011. Case report of an unusual heart abnormality in Rainbow trout (Oncorhynchus mykiss)[abstract]. Eastern Fish Health Workshop. p. 7.

Technical Abstract: An unusual heart abnormality in rainbow trout Oncorhynchus mykiss was recently observed. During the course of a standard hydrogen peroxide treatment (100 ppm) of production rainbow trout (mean weight, 2-3 g) affected with an external bacterial infection, a small percentage of fish exhibited morbidity/mortality. Gross examination of the fish revealed a large protrusion and thinning of the skin between the pectoral fins. Necropsy revealed fish in normal condition with the exception of enlarged cardiac ventricles. Clinical workup of the fish revealed no infectious agents and injection of healthy fish with heart and kidney-spleen-liver homogenates from affected fish resulted in no mortality or abnormalities. Histopathology of the ventricle revealed dilation and severe hypoplasia of the compact layer of the ventricular myocardium. The heart abnormality was further documented in the laboratory during immersion bacterial challenges and also following netting of the fish, which suggests that this condition may be exacerbated by “stress”. The heart abnormality is sporadically observed in small (< 5 g) production fish and resultant mortality is minimal. Cardiac abnormalities are occasionally documented in salmonids and although the cause is unknown, it has been suggested that hereditary/genetic and environmental factors may be involved.