The distribution of some helminth and copepod parasites in tissues of whiting, Merlangius merlangus L., from Manx waters

Abstract

In an examination of 1352 whiting 0–5+ years old from Manx waters it was found that the digeneans Hemiurus communis Odhner and Derogenes varicus Müller were restricted to the stomach. Stephenostomum pristis Looss, Podocotyle atomon Rudolphi and Leci‐thaster gibbosus Rudolphi were most commonly found in the anterior intestine and caeca of mature fish but were found more posteriorly along the intestine of young whiting. The metacercaria of Cryptocoty lingua Creplin were found predominantly in the skin above the lateral line. The fins contained fewer cysts than expected from the area available. Plerocercoids of Grillotia erinaceus Van Beneden mainly infested the musculature of the pyloric stomach and those in the perivisceral cavity were concentrated in the extreme posterior corner. Unencapsulated forms of the nematode Contracaecum clavatum Rudolphi were commonest in the anterior intestine and stomach. Encapsulated forms were most abundant in the liver. The acanthocephalan Echinorhynchus gadi Rudolphi was usually found in the posterior intestine and its presence further restricted Contracaecum to the anterior intestine. In young whiting over two‐thirds of the copepod Clavella uncinata Müller were attached to the operculum and posterior rim but in older whiting the majority were attached to the gill rakers. The first gill arch was the most heavily infested and the middle region of the gill arches contained most parasites. The frequency distributions of most of the helminths described more or less a negative binomial distribution. The frequency distribution of Contracaecum did not conform to either a negative binomial or a Poisson distribution.