Published online by Cambridge University Press: 06 April 2009
A quantitative assessment of the effect of larval Caryophyllaeus laticeps upon its intermediate host, Psammoryctes barbatus, was obtained by comparing the energy budgets of infected and uninfected tubificids from the same natural populationm throughout the course of a year. Measurements of the energy transformations during growth, reproduction and respiration of tubificids indicated some of the effects of the parasite.
Infection had no influence upon the life-span of the host, but progressively decreased its growth and prevented reproduction. By contrast no significant differences were detected between the respiration rates of infected and uninfected animals. Decrease in the production of infected host tissue became apparent as soon as the parasite was detectable. Over the first 6 months loss in production due to the parasite was 50%, and over the whole life-span 59·9%. The production: respiration ratio of infected tubificids was also lower, but differences in assimilation were probably only small. The overall effects of the parasite upon its host population are slight, and the loss in tubificid nutriment available for fish food due to the parasite is less than 5% and of little economic importance. The way in which the parasite actually influences its host's physiology is discussed, and the effect of C. laticeps upon its host's energy budget compared with that of a plerocercoid larva on its fish host.
I should like to thank Dr M. Palmer for the loan of her Warburg flasks, Mr J. Harris for taking samples for me when I was unable to do so,'and Mr G. G. Vickers for many helpful comments and discussions on ecological energetics. I am also grateful to Mr G. Baileyfor combusting the samples for me.