An attempt to balance the energy budget of a host-parasite system

A quantitative assessment of the demand by the parasite Schistocephalus solidus (Miiller, 1776) upon its secondary host, Gasterosteus aculentus L., was obtained by comparing the energy budgets for infected and non-infected fish. Observations on the energy trans-formations during feeding, assimilation, growth and respiration of fishes indicated some overall effects of the parasite upon host metabolism.
Infection resulted in a greater depletion of host food reserws, shown by a marked in-crease in mortality of parasitized fish during starvation. When fed ad libitum upon Tubifex , differences were recorded in the feeding and assimilation rates of fish. By comparison, no significant differences were detected in the respiratory expenditure of infected and non-infected hosts. The computation of energy budgets indicated that fish bearing parasites characteristically exhibited a higher gross efficiency than did fish without parasites. How-ever, subtraction of the calculated effect due to the presence of worms, suggested that the efficiency of infected fish alone, that is, without their parasites, was actually lower than the efficiency of uninfected fish. It is considered therefore that the apparent greater energy turnover in a parasitized fish is due to the parasite being more efficient in its energy trans-formations than is its host.