Observations on the Cestode Eubothrium salvelini in Juvenile Sockeye Salmon (Oncorhynchus nerka) at Babine Lake, British Columbia

Abstract

Infection incidence among 15 brood years of smolts in the period 1952–71 was estimated from smolt and underyearling samples, and among late run fish from the main part of Babine Lake ranged from 6 to 45% (average 26%). In early run fish from the North Arm–Nilkitkwa area it ranged from 5 to 46% (average 22%) in 10 years during 1958–71.Infection intensity changed substantially during 1967; but about one fish in eight, or 200,000 individuals in the early run, carried parasite loads [Formula: see text] of fish weight. Mature E. salvelini (Schrank 1790) averaged 32 mg in weight and 34 mm in length during a period of high incidence and intensity of infection in 1967.Although no proof was found of direct mortality caused by E. salvelini, indirect effects such as inferior growth, poor swimming performance, or aberrant behavior due to large cestode loads may increase host susceptibility to death from other causes.Changes in relative abundance of the zooplankton intermediate host, and midsummer shifts in feeding preferences of young sockeye likely account for increasing infection incidence in June and July, and stable incidence thereafter.