The kidney of rainbow trout, Salmo gairdneri Richardson, in the acute phase of viral haemorrhagic septicaemia: in vivo experiments on the renal excretion of fluid, electrolytes and protein

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Abstract. Kidney function was studied in unanaesthetized rainbow trout, Salmo gairdneri Richardson, with acute infection by VHS virus strain F‐l causing viral haemorrhagic septicaemia. The experiments were performed in diseased and control fish with catheters chronically implanted in the dorsal aorta and the urinary bladder. Glomerular clearance of polyfructosan, tubular handling of fluid and electrolytes and urinary excretion of protein were studied. In diseased fish, plasma concentrations of inorganic solutes were reduced, but plasma osmolarity and systemic blood pressure remained unchanged. Glomerular filtration rate and urine flow, both linearly correlated, were reduced from 5.20±0.40 to 3.08±0.66 ml/h/kg and from 2.51±0.15 to 1.63±0.28 ml/h/kg, respectively (x̄±SEM). The urine osmolarity was augmented due to increased Na and Mg concentrations in the urine. Net tubular secretion of Mg was observed in diseased fish whereas net reabsorption of Mg prevailed in the controls. Decreased renal protein excretion rate prevented a renal loss of protein and, therefore, diminished plasma protein concentrations in VHS‐infected fish may be attributed to extrarenal pathophysiological mechanisms.