Eubothrium salvelini (Cestoda: Pseudophyllidea) Impairs Seawater Adaptation of Migrant Sockeye Salmon Yearlings (Oncorhynchus nerka) from Babine Lake, British Columbia

Abstract

Migrant sockeye salmon yearlings (Oncorhynchus nerka) were captured at the outlet of Babine Lake, British Columbia, in 1979 and 1980 and transported to the laboratory for evaluation of their seawater adaptability in a 24-h challenge test. Fish infected with the cestode Eubothrium salvelini had a reduced ability to adapt to salt water, as evidenced by greater mortality and elevated plasma sodium levels after challenge. The prevalence of infection was 60% in 1979 and 30% in 1980. In 1979, mortality during challenge was significantly higher among infected than among noninfected fish; the elevation of plasma sodium levels in the infected fish was not statistically significant. In 1980, both infected and noninfected fish had improved seawater adaptability compared with the previous year; infected fish did not suffer significantly higher mortality after challenge but their plasma sodium levels were elevated significantly compared with the noninfected fish. The reduced seawater adaptability of infected fish is likely to reduce their ocean survival considerably.