REGULATION OF INFRAPOPULATIONS OF CRYPTOCOTYLE-LINGUA ON COD

To study the infection dynamics of metacercariae of the digenean Crypt ocotyle lingua, wild living Atlantic cod, Gadus morhua, were caged for 18 months close to the shore. Here they were exposed to naturally occ urring transmission stages of the parasite. First, both the abundance and the variance to mean ratio of metacercariae increased, but during the second half of the study the abundance levelled out, and the varia nce to mean ratio showed a significant decrease. Host mortality was ne gligible throughout the study. Based on the relationship between pigme nt spots and metacercariae observed by skin digestion, there was no in dication of density-dependent parasite mortality. We conclude that the infrapopulations of metacercariae on the caged cod probably were regu lated by density-dependent host responses acting against the cercariae .