Abstract
Lernaea cyprinacea, known as an anchor worm, was found on wild ayu Plecoglossus altivelis collected in the Shonai River, Japan, from early June to middle September 2013, with the maximum prevalence of 64.3% in late August. The prevalence was positively correlated with water temperature and standard length of the fish. Most (90%) of parasites were found at the base of the fins. Impact of the parasite on ayu populations might be supported by high prevalence in individuals detained downstream. The parasite also infected four other fishes including Rhinogobius giurinus, Pseudogobius esocinus, Mugil cephalus cephalus, and Carassius auratus langsdorfii; the former three fishes were new hosts for L. cyprinacea in Japan.
