On the host specificity of fish tapeworm

Host-parasite interactions established between Proteocephalus exiguus and its fish hosts have been analysed in two localities in Slovakia. P. exiguus occurred and sexually matured in three salmonid hosts - rainbow trout(Oncorhynchus mykiss), brown trout(Salmo trutta m. fario), brook trout (Salvelinus fontinalis) — and in perch (Perca fluviatilis), first recorded as a final host of this parasite. The parasite usually strictly prefered its principal, most suitable host (rainbow trout) or some other salmonid hosts. The new fish host species (perch) harboured P. exiguus rather frequently, but only in altered ecosystem, if salmonids were not available in sufficient number in the environment. Large adaptive ability of P. exiguus manifested in its survival in four fish hosts of two distant families (Salmonidae, Percidae) and modified seasonality in unusual fish host indicate broader host specificity (stenoxenous in sense used by Euzet & Combes, 1980) than generally attributed to this species. The host specificity in some other Proteocephalus tapeworms is briefly discussed