海産稚アユの遡上生態-1・2-
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概要
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The variations in the number and the body length of anadromous ayu fry in the River Okumo were observed in 1962, and in conformity with the results obtained the suitable time and fish body length for the stock were scrutinized. Results are as follows: 1) The going up of ayu fry began when the river water temperature rose beyond 10°C in the daytime on April 1. The number of anadromous fry suddenly increased at 12°C above, and attained to the maximum at 14-16°C for the second 10 days of the month. After the period anadromous ones gradually decreased in number, and the going up ceased about the middle of May. So it is considered that the optimum water temperature for the going up the river of marine ayu fry is ranged between 14°C and 16°C. 2) All of the fry which had gone up for first 5 days in the season were fallen into the largest size class, 6.5-9.5cm in body length, and those of continued periods, every 10 days period, became small step by step. With approaching to the final of season the body length fell into 4.0-6.9cm, and the going up of ayu fry ceased when the schools composed of 4.5-4.9cm fishes took preferential shares. 3) The rates of the body depth to the condition factor and to the body length are greater in the fishes caught for the beginning period, and the rates gradually fall as days go by, and that shows the fishes of corpulent habit exchanges to those of thin one through the season. 4) From various results mentioned above it is considered for stock of Ayu fry that the river water temperature is desirable to be above 10°C during from the beginning to the middle of April. Concerning to the body length, being above 6.5cm are desirable for the beginning of April and being above 5cm for the middle of this month.
- 社団法人 日本水産学会の論文