Title: Seasonal Variation in the Amount of Zoospore of Aquatic Phycomycetes in Lake Shinseiko
Abstract: 1) The seasonal variation in the amount of the zoospore of aquatic Phycomycetes was studied from October, 1957 to September, 1958 in Lake Shinseiko, Kanagawa Prefecture. The number of the zoospore increased both in spring and autumn, and decreased in summer and winter.2) The vertical distribution of the zoospore varied with different seasons. There were two main types, i. e. the homogeneous distribution and the stratum one. The former appeared during the circulation period and the latter during the stagnation period.3) Seven species were obtained from the lake. Saprolegnia monoica, S. diclina, Isoachlya ecocentrica, Dictyuchus sp. and Aphanomyces sp. were seen from autumn to early spring, and Achlya sp. was found mostly in summer. Pythium sp. was obtained through the year with the maximum in spring and autumn.4) Aphanomyces sp. and Pythium sp. were distributed only in the surface layer during the stagnation period. During the circulation period, however, Aphanomyces sp. was distributed mostly in the bottom layer.5) The zoospore production may be influenced not only by the water temperature, but also by the multiplication of periphytic bacteria. The optimum temperature for the zoospore formation in some species was as follows. Saprolegnia monoica 10-20°, Aphanomyces sp. 5-15°, Pythium sp. 5-30°