| Co-Investigator(Kenkyū-buntansha) |
MATSUSHITA Katsumi Assistant, Dept. of Fish., Fac. of Agr., Univ. of Tokyo, 農学部, 助手 (00012039)
TANIUCHI Toru Lecturer, Dept. of Fish., Fac. of Agr., Univ. of Tokyo, 農学部, 講師 (00012021)
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| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1986: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1985: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
Salmon, due to its characteristic mother stream migration, is considered to have a separate strain in each river, which may show differences in migratory behaviour and utilization characters (economic characters) to various extent from river to river. This project is aimed at registering the strains of salmon in Tohoku district based on the characters such as time of ascending migration, return rate, growth rate, fecundity, egg diameter etc. and giving informations necessary either on transplantation of suitable strain of salmon for any given stream or on artificial breeding.
The ecological characters mentioned above were examined. Originally, each river strain has its own characteristic time of ascending migration. However, it has been changed by the transplantation of eggs from the Tsugaruishi river which has the latest strain. 46 among 93 rivers have shown new late peak and in 26 rivers, the time of ascending have prolonged. In Tsugaruishi river, also, the time of 1978-1980 year-classes, from which large number of eggs were taken out, have become earlier than before.
Males predominate in earlier runs and females in later runs, as said before. Furthermore, males predominate in the strains with early time by ascending. The converse is also true.
In the former days, the body size of fish were larger in the strains with later time of ascending, but such a tendency has not become clear now.
The reproductive characters such as total egg weight, fecundity and egg size vary among years in each river. However, the remarkable differences were observed among rivers. The strain of Izumita river has the smallest egg and is the most fertile. On the other hand, Otsuchi river strain has the biggest egg and the least number of eggs.
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