Abstract
1. Lakes Kusshyaro-ko, Akan-ko, Toro-ko and Shikaribetsu-ko were investigated in 1973 in regard to their bottom fauna,
2. In Lake Kusshyaro-ko, only Spaniotoma sp. (B-5) was found in the profundal zone. The dissolved oxygen was rich and the pH value was 4.2 through the layers from the surface to the bottom at the central part of the lake.
3. In Lake Akan-ko, excepting the azoic zone which extends to the bottom deeper than 32 meters, C. plumosus, Sergentia sp. (B-1) and Procladius sp. (F) occurred widely ; C. plumosus the dominant.
4. In Lake Toro-ko, Chaoborus sp. and C. plumosus are distributed widely on almost all over the bottom. The former made up 59.5% and the latter 33.4% of the total bottom fauna.
5. In Lake Shikaribetsu-ko, the macroscopic animals were scarcely found in the zone deeper than 95 meters, where the dissolved oxygen contents were 0.33cc/l. Tubifex sp. occurred abundantly on the bottom shallower than 75 meters, but chironomid larvae were very scanty.
