The life history of the eye-maggot of the sprat,Lernaeenicus sprattae(Sowerby) (Copepoda, Lernaeoceridae)

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Abstract
Material was collected from the inner Oslofjord; planktonic stages with a new neuston net, and other material directly from Sprattus sprattus (L.), caught by beach seine. The morphology of a complete series of developmental stages of the parasite is illustrated, described, and compared with that of related genera, particularly Lernaeocera branchialis (L.). Two free-swimming naupliar stages and a copepodid stage are followed by a brief grasping stage (second copepodid) on the sprat, and four chalimus stages i.e. four external parasitic stages (nymphal stages) on the host. In the second pelagic phase, the males presumably die soon after copulation whereas the females, after a molt, again settle on a sprat and are found either free on the sprat or inside its eye. In the eye the parasite undergoes a marked transformation and appears finally as the well known mature female with egg strings in which part of the larval development takes place before hatching. Fourteen different ‘stages’ are described, but the number of ‘instars’ is smaller. Studies so far point to an 11-stage cycle of development including the adult. Similarities in ontogeny between Caligidae, Lernaeoceridae, and Lernaeopodidae seem to show that they have a monophyletic origin in spite of striking differences in the morphology of their adult. Identification of the nauplii and copepodids was based on developing eggs from adult parasites, the others on comparisons of the different stages throughout the whole life cycle. Behaviour of the developmental stages was also studied. Growth curves based on measurements of all specimens shows that every developmental stage was detected, but the rate of growth can only be suggested because the duration of each stage is not known. Each stage of L. sprattae up to the second free-swimming phase is much longer than the corresponding stages of L. branchialis. The distinguishing characteristics for stages of L. sprattae are pointed out. Some new morphological data of mature female are also given, e.g. descriptions of the teeth and serrated lamellae of the mouth cone. These are present in all female stages and the free-swimming male and are the most significant differences between Lernaeenicus and Lernaeocera.

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