Geographical variations in infection by larval Anisakis simplex and Contracaecum osculatum (Nematoda, Anisakidae) in walleye pollock Theragra chalcogramma stocks off Hokkaido, Japan

Abstract

Stocks of walleye pollock Theragra chalcogramma collected from: (i) the Sea of Japan (off Rebun Island and Kumaishi); (ii) the Pacific coast (off Shikabe and eastern Hokkaido); and (iii) Nemuro Strait off Hokkaido, northern Japan, were examined for anisakid nematodes during December 1999 to February 2000, and the prevalence and abundance of Anisakis simplex and Contracaecum oscula tum larvae were compared among the various sampling sites for fish of the same size and age. Anisakis simplex was generally more abundant than C. oscula tum. Infection by A. simplex varied between the aforementioned stocks of walleye pollock as well as within stocks, whereby fish from off Rebun Island and Nemuro Strait were infected the most, followed by those from off the Pacific coast and Kumaishi. Infection by C. oscula tum differed between the host stocks, and C. oscula tum was the most abundant among the fish from Nemuro Strait. The infection variations seemed to be due to differences in host growth rate, host feeding habit, and the distribution of marine mammal final hosts. The results indicate that these two larval nematodes are useful biological indicators for the population study of walleye pollock in Japanese waters.

Relationship between sea-surface temperature and catch fluctuations in the Pacific stock of walleye pollock in Japan

“…Geographical differences were observed in the peak month with the highest catch: September in Hidaka, October in Iburi, and December in Oshima, which is spawning ground. As a whole, geographic shifts of months with increases or decreases in the catch were considered to reflect migration of adult individuals that came back to Oshima via Hidaka and Iburi 13–17 …”

Occurrence and identification of Anisakis spp. (Nematoda: Anisakidae) isolated from chum salmon (Oncorhynchus keta) in Korea

“…The occurrence of anisakid nematodes in the fish muscle is also unappealing to consumers because they can reduce the value of the product (Aspholm 1995). The presence of anisakid nematodes have also been used as a biological indicator for ecological study such as stock characterization and discrimination, migratory movement, host diet, and feeding habits (Konisi and Sakurai 2002;Podolska et al 2006;Klimpel et al 2007;Mattiucci et al 2007). …”

Infection of the Japanese common squid, Todarodes pacificus (Cephalopoda: Ommastrephidae) by larval anisakid nematodes

“…Near Hokkaido, the prevalence and abundance of A. simplex in walleye pollock are highest in the Nemuro Strait stock (Konishi and Sakurai, 2002), which feeds in the Sea of Okhotsk and the Oyashio region (Tsuji, 1973;Ishino, 1993). In these areas, euphausiids are a major crustacean host of A. simplex (Oshima, 1969;Shimazu, 1982;Hays et al, 1998) and a dominant prey of walleye pollock (Konishi and Sakurai, 2002), so predation on euphausiids may be an important factor that determines infection levels. Off the Pacific coast of Hokkaido, small walleye pollock feed mainly on euphausiids, copepods and amphipods, whereas larger walleye pollock are more piscivorous and feed on larger prey, as well as on the aforementioned crustaceans (Iizuka et al, 1954).…”