Host and site selection by larval stages and adults of the parasitic copepod Lernaeenicus sprattae (Sowerby) (Copepoda,Pennellidae) in the Oslofjord

Sprat caught by beach seining during the period 1977–1980 were examined for adult Lernaeenicus, and both sprat and herring caught in 1981–1983 were examined for all parasitic stages. Lernaeenicus was never found on herring. Adult L. sprattae were always found in the sprat's eye, usually (89%) in the upper rear quadrant of the eye. Double and triple infection of one or both eyes were found. Infection experiments support results from field work. The sprat is the only intermediate and final host of L. sprattae. In laboratory experiments, copepodites showed no preference for particular size groups of sprat. The infective stages, copepodid and adolescent female, are both initially randomly distributed on the host before the copepodites move towards the fins and the gravid females to the eye.