広島大学東広島キャンパス内にある溜池のぶどう池で，2011–2016 年の5 月下旬にブルーギルLepomis macrochirus Rafinesque を採集して，カイアシ類の1 種，イカリムシLernaea cyprinacea Linnaeus の寄生状況を調べた。ぶどう池に在来魚はほとんど生息しないため，イカリムシは国外外来種でぶどう池に多産するブルーギルを宿主に用いて個体群を維持していると考えられた。調査した6 年間の5 月下旬の寄生率と寄生強度はそれぞれ1.5–5.8% と1 個体と低く，採取されたイカリムシの多くは卵嚢をもっていなかった。これは，この時期にイカリムシの繁殖が活発ではないために，感染がぶどう池のブルーギル個体群に広がっていないためと考えられた。ブルーギルの鰭基部に寄生するイカリムシが多かった。, The occurrence of the copepod parasite Lernaea cyprinacea Linnaeus on bluegill Lepomis macrochirus Rafinesque was studied in late May for six years, from 2011 to 2016, in Budo Reservoir within the campus of Hiroshima University in Higashi-Hiroshima, Hiroshima Prefecture, Japan. Bluegill was introduced in 1960 from the United States to Japan, where it has established its populations in numerous freshwater bodies, including this reservoir. The abundance of domestic fish species was very low in the reservoir, and L. cyprinacea exclusively utilized bluegill as its host. The prevalence of L. cyprinacea infection was stably low (1.5–5.8%), and its intensity of infection remained at 1, perhaps because this parasite did not actively reproduce in late May and its infection did not spread to the host population in the reservoir. Most L. cyprinacea were found on the host’s body surface near the base of the fins.