彩色した沈垣網の効果について

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This experiment regarding influence of colours of fish net, was performed in ordey to observe the frequency of transfer of fishes over several models of fencing net in a center tank. The tank is of wood painted white inside, 72cm. long, 52cm. wide, with a water depth of 20cm. (Fig. 1) The fish used were 10 individuals of Acheilognathus lanceolate (Yari-tanago) of average total length 4.5cm. and they were liberated in the tank. As model of under-water fencing nets, 5 tinplates 52cm. long and 14cm. high were painted with black, white, red, yellow and blue enamel. The tinplate as fencing net was kept under water in the center of tank, leaving a space of 6cm. between the water surface and the top of the plate. (Fig. 1.) The number of transfer of fishes over the tin-plate were counted during 10 minutes on each colour plate. This was repeated for 29 times during a period of several days. (Table 1.) Averages of the frequency of transfer on each colour is shown in Fig. 2. These averages, when compared, show significant difference. In almost all combinations the significance in level was 1 or 5% excepting combinations of red and yellow, and white and blue. (Table 2.) Therefore, the black, red and yellow have less stopping effects against the transfer of fishes. On the other hand, the effects of the white and blue are obviously more effective and these corresponded to a septum of semi-transparent vinyl film which was kept in the tank leaving only a space of 2cm. over it for the fish to pass through. Also, the effects of the red and yellow corresponded to the same septum which was kept in the water leaving a space of 6cm. (Reference 17)
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彩色した沈垣網の効果について

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