Populations of Bothriocephalus claviceps (Goeze) (Cestoda) in the European eel, Anguilla anguilla (L.), in three localities in southwest England

The population biology of Bothriocephalus claviceps (Goeze) has been investigated in the European eel, Anguilla anguilla (L.), in three localities in southwest England. Monthly changes in prevalence and abundance show no statistically significant seasonality, in contrast to growth and reproduction of the cestode. The cestode reaches maximum size and becomes gravid mainly in summer. Gravid cestodes die and are lost soon after reproduction. This overlaps with recruitment of the new generation into eels, and may result in a rapid increase in infection levels and in a more over-dispersed distribution of the parasite in some localities, or in a more gradual change in infection levels and over-dispersion in others. Development and growth of the new generation may cease until the following spring, or continue at a slow rate over winter. Parasite numbers in each host decrease well before they actually reach maturity, since the majority of gravid individuals are present in those eels which harbour only one parasite. This suggests that few cestodes develop to maturity and most are lost from hosts as development proceeds.