養殖ゴイにおけるDactylogyrus extensus及びD.minutusの寄生率の季節的変化

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From May in 1975 to October in 1976, field investigations were made on dactylogyrids infestation on carp cultured in ponds at Hiroshima Prefectural Freshwater Fish Experiment Station. The results obtained are summarized as follows: 1) Dactylogyrus extensus and D. minutns were observed on fish of all ages almost throughout the year. 2) Apparent seasonal changes in abundance of both the dactylogyrids were recognized, and the changes seem to depend mainly on the water temperature. 3) D. extensus and D. minutus increased in abundance in the spring and the fall. The incresse of the former species was remarkable in the spring, and that of the latter in the fall. Both the species decreased conspicuously at the mid summer. 4) The same tendency of the above-mentioned changes in D. extensus was confirmed by experiments. D. extensus apparently increased in number with artificial raise of water temperature from 11°C to 20°C, and decreased sharply when the water temperature was over 20°C and reached about 25°C.
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