Infestation dynamics of external parasites of saithe (Pollachius virens) from the North and Norwegian Seas.

An attempt has been made to examine the saithe's external parasites with respect to host age and the reproduction time of Clavella adunca in the North Sea. 1835 specimens of Pollachius virens caught in 1976-1980 and 1986 were examined. They were infested with Diclidophora denticulata, Udonella caligorum (Monogenea) and Clavella adunca, Lepeophtheirus pollachius, Caligus elongatus (Copepoda). The large number of adult females of C. adunca in winter and spring, the juvenile forms in summer and forms of 4th developmental phase autumn suggest that the reproduction cycle runs over the year in the North Sea with the peak between the late spring and early summer. The intensity values of infestation are highest for sexually mature fish but fall in older ones.