Digenean parasite communities in flatfishes of the Scotian Shelf and southern Gulf of St. Lawrence

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Abstract
Prevalence of digenean parasites in four major flatfishes of the Scotian Shelf and southern Gulf of St. Lawrence, American plaice (Hippoglossoides platessoides), yellowtail flounder (Limanda ferruginea), witch flounder (Glyptocephalus cynoglossus), and winter flounder (Pseudopleuronectes americanus), is compared between hosts in relation to geographic distribution, season, feeding behavior, and fish length. The 13 parasite species indicate overlap of feeding habits among hosts but also considerable diversity in feeding behavior, supporting the evidence from examination of stomach contents. Prevalence of digeneans in different final hosts varied between geographic areas and may be used to characterize the populations of the comparatively sedentary flatfish populations. Seasonal variation in prevalence was consistent from area to area but differed between parasites, from the expected increase in summer in some, concomitant with increased feeding, to a winter increase in others, probably related to a seasonal change of diet. Fish length had little effect on parasite prevalence in yellowtail flounder and witch flounder but had a notable effect on plaice and winter flounder from the Gulf of St. Lawrence, again apparently related to change of diet.