Abstract / Introduction / Summary:
Eight postmetamorphic adult females of Lernaea cyprinacea Linnaeus, 1758 were collected from two (prevalence, 14.3%) of 14 adult Amur sticklebacks, Pungitius sinensis (Guichenot, 1869), in an irrigation canal at Sumiyoshi (43º55′02″N, 144º07′28″E) in Memanbetsu, Ozora, eastern Hokkaido, northern Japan, on 22 July 2021. Each infected fish harbored four females of L. cyprinacea, and all of the females collected were ovigerous. The females inserted their cephalothorax and anterior part of the neck into the host tissues, and the posterior part of the neck and the trunk protruded externally. Most of the females were attached to the base of fins, such as the pectoral, dorsal, and anal fin, and filamentous green algae were associated with some of the females. This collection of L. cyprinacea represents its second record from eastern Hokkaido, where this parasite was previously recorded from fishes in two lakes, Lake Toro and Lake Shirarutoro. One of the hosts reported from the latter lake was reported as Pungitius p. pungitius (Linnaeus, 1758), but it has been currently regarded as P. sinensis. The collection site in this study lies in the subarctic region (annual mean air temperature, ca. 7.0ºC; snowfall occurring from late October to late April), and the reproduction of L. cyprinacea may be lower there than in the temperate region of Japan.
