Distribution of Cryptobia salmositica, a haemoflagellate of fishes, in British Columbia and the seasonal pattern of infection in a coastal river

Abstract

A survey of adult Pacific salmon (Oncorhynchus spp.) from 1981 to 1983, along with other observations, demonstrated that in British Columbia Cryptobia salmositica was confined to tributaries of the Fraser River, coastal rivers adjacent to this river, and rivers on Vancouver Island. Adult salmon from the Queen Charlotte Islands and the Bella Coola, Skeena, and Nass rivers in British Columbia and the Yukon River in the Yukon Territory were not infected. The distribution of C. salmositica may be explained by events of the Wisconsin glacial and postglacial periods. Seasonal variability in prevalence and intensity of infection of C. salmositica in the Big Qualicum River, a coastal river on Vancouver Island, is related to the seasonal return of adult salmon in late summer and autumn, and the concomitant increase in abundance of the leech vector, Piscicola salmositica. Prevalence and intensity of infection in juvenile salmonids in this river also increased during autumn. Cryptobia salmositica was present in resident sculpins (Cottus aleuticus) throughout the year; however, the prevalence did not begin to increase until December, coincident with the postspawning decline in salmon numbers in the river. The finding of C. salmositica in cutthroat trout (Salmo clarki) from the Big Qualicum River constitutes a new host record.