Abstract / Introduction / Summary:
An ovigerous female specimen of a freshwater fish parasite Argulus coregoni Thorell, 1864 was found in the collection of the Lake Biwa Museum, Kusatsu, Shiga Prefecture, central Japan. This specimen was collected as a detached individual by a small trap net installed for a fish fauna study in the middle reaches of the Nagara River at Hotoshima (now Homyo) in Seki, Gifu Prefecture, central Honshu, Japan on 5 September 1986. The specimen is briefly described. It might have detached from an ayu Plecoglossus altivelis altivelis (Temminck and Schlegel, 1846), which is the important riverine host of A. coregoni, in the trap net, or a detached individual drifting downstream might have been trapped.
