抄録
Swimming Chironomus plumosus larvae were collected from the surface water layer using a fish larva net in the daytime and at midnight of June 11,1970 in Lake Suwa (eutrophic lake situated 759 m above sea level, with an area of 14.45 km^2 and a maximum depth of 6.5 m, in central Japan). Based upon the comparison of the body length distributions of the larvae collected at the surface and bottom it is concluded that the Chironomus larvae from the 1st to the late 4th instar stages make swimming behavior under the windless condition both in the daytime and at night. This result suggests that the duration in which the larvae keep the swimming behavior is far longer than experimentally estimated by NOSE (1961) and this behavior makes the larvae even at the 4th instarstage easily to be eaten by pond smelt (Hypomesusolidus), a typical zooplankton feeder inhabiting the lake.
