千曲川産アユの成長と成熟度について

Abstract

In Tikuma River, no fish goes up the stream being prevented by dams, so many young “Ayu” (Plecoglossus altivelis) have been transplanted every years. I investigated on the growth and the development on these samples which caught with weirs at 6 stations, Ueda and it's neighbourhood within 35km. in Tikuma River (Fig. I, Tab. I) in the matured season 1946. The differences were found among these stations on the growth and the development (Tab. 3-5), the growth was inferior, and the development earier at these upper stations, Gozigawara, Otiai and Iwasita; and the growth was superior and the development later at these lower stations, Gosyo, Simonozyo and Simohanga. In each station, these fishes which the growth was relatively superior, the development was later, that would be caused mostly on the temperature of water, but at Gozigawara above all, the growth was the worst, it seems to due on the existence of dam at upper stream and drain at lower stream of the power plant, even if there were other causes. So the production of Plecoglossus altivelis in this district to increase by transplanting more seedlings in these stations where they thrived, it will be better to carry on such as suit place for live as Gosyo, Simonozyo and Simohanga in the other.