Pathogenicity of Vibrio harveyi to salmonids

Our of 19 Vibrio harveyi isolates obtained from a diversity of hosts and geographical locations, 14 were pathogenic to rainbow trout, Oncorhynchus mykiss (Walbaum), and Atlantic salmon, Salmo salar L., with mortalities of up to 100% following intraperitoneal injections of 10(6) cells fish(-1). The extracellular products (ECPs) of only five pathogenic isolates were harmful to fish. Both pathogenic and non-pathogenic cultures produced ECPs containing caseinase, gelatinase, phospholipase, lipase and haemolysins. Vibrio harveyi VIB 645, which was the most pathogenic isolate, produced ECPs with a maximal effect on salmonids from preparations obtained by using cellophane overlays on tryptone soya agar supplemented with 1% (w/v) sodium chloride with incubation ac 28 degrees C for 24 h. This preparation contained the highest titre of haemolytic activity to Atlantic salmon (1:256) and rainbow trout (1:32) erychrocytes.