Post-cyclic transmission in Pomphorhynchus laevis (Acanthocephala)

A series of laboratory experiments was conducted to investigate the possibi lity of post-cyclic transmission in Pomphorhynchus laevis (Muller, 1776). R ainbow trout Onchorhynchus mykiss (Walbaum) were exposed to P. laevis in na turally infected Coitus gobio Linnaeus, Noemacheilus barbatulus (Linnaeus), Phoxinus phoxinus (Linnaeus) and Leuciscus cephalus (Linnaeus) and sacrifi ced one month after infection. Post-cyclic transmission was possible from a ll four species even though they came from three families and differed in r espect of their status and suitability as hosts of P. laevis. There was no selection for or against either sex of P. laevis, parasites grew in the rai nbows and they occupied the same, normal site in the intestine of rainbows irrespective of source host. Post-cyclic transmission of gravid parasites c ould occur From C. gobio but not from L. cephalus. It is believed that this failure to transmit larger parasites of either sex reflects the age and so development of the proboscis bulb of P. laevis and the extent of the host encapsulation response rather than size or stage of maturity per se. Post-c yclic transmission has the potential to be important in nature.