Incidence and intensity of Cyathocephalus truncatus and Schistocephalus solidus infection in Gasterosteus aculeatus

Abstract

C. truncatus, a cestode usually found in salmonids, and plerocercoids of S. solidus are reported from a population of G. aculeatus on the Queen Charlotte Islands, British Columbia [Canada]. Adult C. truncatus attached at the anterior of the intestine adjacent to the pyloric sphincter, whereas in salmonids the pyloric caeca is the usual attachment site. Mean intensities of infection for C. truncatus and S. solidus were 2.7 (maximum 26) and 3.4 (maximum 87), respectively, with intensities increasing in larger fish. The highest incidence of C. truncatus infection was from Feb.-May (80%) and for S. solidus, from April-Sept. (50%). Infection rates for C. truncatus during different seasons and among different length classes of fish were directly correlated with the relative abundance of amphipods (the intermediate hosts of C. truncatus) in the fish stomachs. Possible modification of host feeding behavior is indicated by a relative increase in the consumption of amphipods by infected fish.