Effects of the electric dam erected in the down stream of Kuma River in the year 1954, upon the development of “ayu, ” Plecoglossus altivelis

Abstract

Kuma River of the Kumamoto Prefecture is famous in producing “ayu, ” Plecoglossus altivelis, of good quality, due to the suitable environmental conditions. Quite recently, however, utilization of the stream for the sake of generation of electricity necessitated to erect the darn of 34 meter high at the down stream in order to construct water reservoir. The Prefectural Government started the works last year and the dam. which is not provided any fish ways has been completed on 10 th of December, 1954, shutting up completely the passway of the anadromous fishes especially.
Consequently, complains of fishermen and inhabitants of the upper streams opposing to the policy of the Government paying no attention for fish culture, especially to keep good name of Kuma River in “ayu” fishing, became furious. In order to solve this hard problems, viz, electricity nor fishing industry, authorities of the Government promissed to liberate large number of “ayu” fry in the upper streams per year, to meet the both ends.
This attempts has been fulfilled for the first time in the spring ot the present year since, fries of sea-run form caught at the estuary of Kuma River and other parts in Kiushu as well as dwarf land-locked form of the Lake Biwa and Ikeda being libertated in the main and branch streams of Kuma River.
In the present paper are shown morphological differences between sea-run form of “ayu, ” grown at the both sides of the dam; effect of suitable baits upon development of land-locked dwarf form of “ayu” originated in the Lake Ikeda ; distinction between sea-run form and land-locked form of “ayu” after fattening, from the stand-point of scale figurations, etc.