Prevalence of the hemiurid trematode Brachyphallus crenatus in the stomach of juvenile masu salmon Oncorhynchus masou in the coastal waters near Cape Erimo, Hokkaido, Japan
2019
Asami, H. (Salmon and Freshwater Fisheries Research Institute, Hokkaido Research Organization, Eniwa, Hokkaido (Japan)) | Hayano, H. | Mano, S. | Nagata, M.
Prevalence of the hemiurid trematode Brachyphallus crenatus in the stomach of the juvenile masu salmon Oncorhynchus masou collected in the coastal waters near Cape Erimo off the Pacific coast of Hokkaido was investigated. Juvenile salmon were sampled at two different times of the day (early morning, 5:00, and day-time, 13:00) on June 10, 1994, using set nets extending, from the shore to offshore areas at three stations. A total of 127 juveniles were collected (41 individuals in the early morning and 86 individuals during the day). Most of the juveniles were captured at the shore stations. Five tagged juveniles were also found at the shore stations during the day. The fork lengths of the juveniles collected at shore were smaller than those of the juveniles caught offshore. The ratio of small juveniles (<20 cm) caught was about 50 % during the day, and about 29% in the early morning. B. crenatus was present in over 95% of the total juvenile salmon collected during the early morning and day. Mean intensity of occurrence was higher in the early morning than during the day for both the males and females. A positive correlation was found between the fork length and intensity of B. crenatus. Differences in the prevalence incidence during the two periods of the day might relate to the differences in sea entry sites or in the time spent at sea. The effectiveness of B. crenatus as biological tags of juvenile salmons is discussed.
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