Vertical Distribution and Diel Migration of Isaza, Chaenogobius isaza, Pisces in Lake Biwa

概要

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Midwater trawling surveys were carried out to determine the diel vertical migration of Isaza from summer to autumn. During these seasons, Isaza stay on the lake bottom in the daytime ; shortly after sunset they swim up and restrict themselves to a thin stratum ranging from the upper layer of thermocline to the lower layer of epilimnion. After midnight most of them seem to descend. The water temperature of this stratum varies from 23℃ to 16℃ from summer to autumn. On the other hand, the temperature of the lake bottom is about 8℃ throughout the year. This means that Isaza are exposed to conspicuously fluctuating temperatures daily and annually in their diel vertical migration. One reason for the migration of Isaza might be connected with an abundance of zooplankton in the upper stratum, on which Isaza mainly feed. Isaza can tolerate water temperatures as high as 23℃ and feed on zooplankton in the upper layer, contrary to the common view that Isaza is a cold water species associated with deep water in warm seasons.
社団法人日本動物学会の論文
1981-06-25