Total Sialic Acid, Oxidative Stress and Histopathological Changes in Rainbow Trout Saprolegniasis (Oncorhynchus mykiss)

Saprolegniasis is known as one of the most important fungal diseases of salmonids along with high mortality and economic problems. One hundred and seven fish suffering from cutaneous Saprolegnia infections and the same number of healthy fish were selected and blood parameters along with histopathology assay were performed in all ones. The results indicated a significant increase (P <= 0.01) in total sialic acid, malondialdehyde, urea, creatinine, aspartate aminotransferase, total protein in plasma and a decrease in glucose, catalase, glutathione peroxidase and paraoxonase. Meanwhile, no significant alterations of alanine aminotransferase and superoxide dismutase were revealed in infected fish. Also, the histopathological findings observed in liver, especially glycogen storage and fatty inclusion and melanomacrophage centres in spleen. Tubular vascular degeneration along with cystic formation was identified in kidney. The results suggest that saprolegniasis develops substantial histopathological and blood profile changes in rainbow trout and recommend to pay more attention on some biochemical profiles such as MDA and TSA, due to cell health and defence against fungus on the skin respectively, along with hepatocyte function index (aspartate aminotransferase) and nitrogen metabolism (creatinine and urea) during disease management.