The effect of temperature upon the establishment and survival of the cestodeCaryophyllaeus laticepsin orfe,Leuciscus idus

Farm-reared Leuciscus iduswere experimentally infected with the intestinal tapewormCaryophyllaeus laticeps, and maintained at different temperatures. At 12 °C and lower temperatures there was an initial loss of parasites after infection, but the survivors persisted for up to 1 month. At 18 °C only temporary survival of the parasite was possible, and worms were killed and rejected after 3 days. Experimental transplants to fresh hosts after 2 days indicated that the factors responsible for the death of the parasites became effective within this period.Neither inhibition of peristalsis nor host starvation affected the parasite's survival. The speed of the response to the parasite indicates that circulating antibodies produced in response toC. laticepsand directed specifically against it cannot be involved in the rejection. Other possible mechanisms of rejection are discussed, together with the significance of the results to the interpretation of data based on field observations. I should like to thank Mr J. Harris for allowing me to refer to some of his unpublished data and for helpful discussions.