Studies on the pathogenesis of vibriosis in coho salmon Oncorhynchus kisutch (Walbaum)

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Abstract
Juvenile coho salmon Oncorhynchus kisutch (Walbaum), cultured in fresh water, were experimentally infected with highly virulent Vibrio anguillarum, and various haematological and biochemical parameters were compared between moribund and non‐infected control fish. In addition, endotoxin, culture supernatant, and cell lysate preparations of V. anguillarum were tested separately and in combination to assess their roles in mediating pathological effects.The haematocrit, haemoglobin, numbers of red and white blood cells and plasma, total protein, albumin, β2 globulin, chloride, sodium, osmolality and alkaline phosphatase levels were all decreased in infected fish compared to controls. Erythrocyte fragility and plasma glucose, potassium, lactate dehydrogenase (LDH), and glutamic oxaloacetic transaminase (GOT) levels were increased in infected fish.No mortality nor significant changes in haematocrit or plasma protein occurred in fish injected intraperitoneally with 35 mg/kg (1 mouse LD50) of V. anguillarum endotoxin, with culture supernatant fluid, cell lysate, or with combinations of the three preparations. There was, however, a decrease in plasma protein concentration in coho injected with 355 mg/kg (10 mouse LD50s) of endotoxin, but no mortality nor significant change in haematocrit.