Biology of parasite populations: population dynamics of bothriocephalids (Cestoda-Pseudophyllidea) in teleostean fish

Relationships between sympatric populations of four species of Cestoda belonging to the genus Bothriocephalus (B. barbarus. B. gregarius, B. funiculus and B. scorpii) and populations of their respective hosts Scophthalmus rhombus, Pserra maxima, Ciliata mustela and Myoxocephalus scorpius were investigated. The parasites were overdispersed within their host populations. The mean intensities of B. burbarus were 1.59 (s.d.=0.83) in the Mediterranean (Gulf of Lions) and 1.25 (s.d.=0.53) in the Atlantic (coasts of Brittany). The mean intensities of B. gregarius were 62.3 (s.d.=49.7) in the Mediterranean and 14.06 (s.d.=18.48) in the Atlantic, compared to 1.78 (s.d.=0.3) for B. funiculus and 21.6 (s.d.=17.3) for B. scorpii. The distribution of prevalence of B. gregarius corresponded to a lognormal distribution while those of B. barbatus and B. fwticulus corresponded to negative binomials. No differences in infection could be related to host sex. The parasitization of B. gregariusdepended on host size. In brill, infection by E. barbatus was independent of host size and remained stable after the fish reached 180mm in length. Parasitization of turbot by E. gregarius was lower in young fish (≤110–150 mm) and increased with the host size. Compared to the Atlantic populations of B. gregarius and B. barbatus, the Mediterranean populations were more frequently and intensively infected. The differences in the population dynamics of B. gregarius and B. barbarus would appear to depend on whether or not the life cycle involves a paratenic host.