Interactions between the acanthocephalansPomphorhynchus laevisandAcanthocephalus anguillaein rainbow trout: testing an exclusion hypothesis

Abstract

SUMMARYRainbow trout were infected simultaneously with cystacanths of the two acanthocephalan speciesPomphorhynchus laevisandAcanthocephalus anguillaein the laboratory. Infections consisted of varying proportions of the two species (from 0 to 100%) at low (20 cystacanths) and high (60 cystacanths) levels. Fish were sacrificed at 7, 56 and 112 days post-infection (p.i.) and the parasites recovered. At low-level infections there was a high degree of overlap in the range of intestine occupied by the two species (44·12 %) and no evidence for interspecific competition affecting either species. At high-level infections the establishment of both species was unaffected by the presence or number of individuals of the other species. The survivorship and the range of intestine occupied byA. anguillaewere found to be reduced in the presence ofP. laevis. The interaction was one-sided, asP. laevisremained unaffected byA. anguillae, and so indicated interference competition. The possibility that both intraspecific and interspecific competition are implicated in explaining the distribution of the two species in the British Isles is discussed.