A Quantitative Study of Economically Important Parasites of Walleye Pollock (Theragra chalcogramma) from British Columbian Waters and Effects of Postmortem Handling on Their Abundance in the Musculature

Abstract

The identity of parasites infecting the musculature and body cavity (including external surfaces of viscera) of walleye pollock (Theragra chalcogramma) collected from two British Columbian localities, their distribution within the host's musculature, and the influence of host sex, length, and method of postmortem handling on parasite prevalence and abundance were determined. Three parasite species were found only in the musculature (Pleistophora sp., pseudophyllidean plerocercoids, and Phocanema decipiens (Krabbe, 1878) larva), two species only in the body cavity (Contracaecum-type larva and Hysterothylacium aduncum (Rudolphi, 1802) larva), and two species in both sites (Anisakis simplex (Rudolphi, 1809) larva and Nybelinia surmenicola Okada in Dollfus, 1929 plerocercoid). In the musculature most A. simplex and N. surmenicola infected the region surrounding the body cavity, with A. simplex being distributed more anteriorly, while most pseudophyllidean plerocercoids occurred in the caudal region. No preferred site of infection was observed for P. decipiens larvae. No statistically significant differences in infection with any of these helminths occurred between right and left body musculature. For pollock of similar lengths, males were more heavily infected than females with larvae of A. simplex and plerocercoids of N. surmenicola. Three species (A. simplex, N. surmenicola, and Pleistophora sp.) occurred with greater prevalence or abundance in larger fish. Storage of eviscerated and round pollock from the Strait of Georgia on ice at 3 °C for periods of up to 7 d did not result in any significant change in the prevalence of infection or abundance of parasites in the musculature. The abundance of these parasites in pollock from Queen Charlotte Sound, northern British Columbia, appears similar to that previously reported for some other areas of the North Pacific Ocean (although not as high as the most heavily infected stocks of the northwest Pacific) while their abundance in fish from the Strait of Georgia, southern British Columbia, appears to be the lowest for any pollock stock examined.Key words: walleye pollock, Theragra chalcogramma; economically important parasites, Pleistophora sp., pseudophyllidean plerocercoids, Nybelinia surmenicola plerocercoid, Phocanema decipiens larva, Contracaecum-type larva, Hysterothylacium aduncum larva, Anisakis simplex larva, British Columbia