八ヶ嶽湖沼群の湖沼学的研究-2-

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During the limnological study (1955) of Lake Shirakoma, the authors came across a noticeable occurrence of the association of pelagic water-mite, Piona (Piona) carnea (KOCH). Though this is not uncommon, its regular and rich occurrence, and also its excellent swimming mood, particularly attracted our interest. And thus the authors were naturally led to make a brief observation of this species. The result of the observation shows that the adult form is found to dominate during the period from late May to early June. Including the young, however, the greatest abundance is seen during early August. The disappearance of the species during the months from October to May, seems to show that it hibernates during this period in or on the bottom of the lake. The spawning of the species culminates in late July to early August, the spent animals dying out soon after the spawning. The maximum size of the eggs is 237.5μ, in diameter, the number of eggs per individual being about 32. The largest body length is 2362.5μ, in the female, and 1837.5μ, in the male. These dimensions, however, vary with individuals. It is worthwhile to note that the pulps and pedals of small individuals are larger than those of larger individuals. The habitat of the above species, Lake Shirakoma in Nagano Prefecture, is a typical Japanese volcanic lake. The lake is situated at such a high altitudes as 2115m, its maximum depth being but 8 meters.
社団法人日本水産学会の論文