Evidence for a Dynamic Equilibrium in the Incidence of Cestoda and Acanthocephala in the Intestines of Freshwater Fish

Abstract

AS Hopkins observed¹, following an examination on the seasonal variations in the incidence and development of the cestode Proteocephalus filicollis (Rudolphi, 1810) in the stickleback Gasterosteus aculeatus L., the significant point in the host–parasite relationship, usually overlooked, is that the incidence of the parasite in the host throughout the year is a dynamic equilibrium. Hopkins clearly showed that less than 1 per cent of the worms which became established in the intestine of the stickleback survived to become gravid. Thus, from the evidence, Hopkins deduced that the parasite population in the intestine of the stickleback was in dynamic balance, that is, the resultant point of equilibrium was the product of gain and loss of worms from the host.