The parasites of Pacific halibut (Hippoglossus stenolepis) in the eastern North Pacific: host-level influences

Abstract

Fifty-nine metazoan parasite taxa were identified from 536 Pacific halibut (Hippoglossus stenolepis) of three size classes (recruits (<10 cm), juveniles (10-55 cm), and subadults/adults (55-102 cm)). Pacific halibut harbor parasite communities that are among the richest and most abundant found in those marine fishes studied to date. The parasites are largely host generalists, being found in a wide variety of marine fishes. These three features appear to be due, in part, to the interplay of the large size, wide diet, extensive mobility, and long life-span of halibut, plus the lack of specificity in the marine system and the ability of marine parasites to be transferred trophically from prey fishes to piscivorous fishes. The parasite community in halibut is more similar to those in other flatfishes than to those in ecological analogs, suggesting that phylogeny is an important determinant as well. There are no differences in infections due to host sex. Recruits harbor few parasites, but parasite species and particularly individuals accumulate with host age and length and reflect the shift from a crustacean to a fish diet. Growth rate influences the number of parasite individuals in a given fish, probably reflecting food intake. The smallest fish in the 5-, 6-, and 7-year age-classes have more parasite individuals than slightly larger fish in the same age-class and weigh less than expected for their size; they may be debilitated by parasites.