魚の遊泳運動におけるπ効果現象-1-水平反転運動

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In this study, the correlation between the width of the horizontal U-turn motion and the body width of the fish was investigated. The experiments were carried out in the waterway set up at the bottom of the circulation-type large tank. The fish used were gold fish, Carassius auratus. These fish were made to be swimming against the flowing current in the waterway specially prepared with the two pieces of plastic plates (Fig. 1). As the experimental condition, the current velocity was assorted into the 3 grades, the interval of the waterway was arranged into the 8 grades (Fig. 2). The electric stimulus was given the fish just before passing between the both electrodes for U-turn motion of the fish. The experiments under the same condition were repeated three times on each fish. The results obtained are as follows; (1) The body width may be regarded as the fittest factor of the U-turn motion (Fig. 2). The widths of the waterway in which the U-turn motion of fish can take place aptly were observed to be π-times of the body widths. (2) Through the results of Fig. 6, the relationship between the swimming width (L) and the radius of the curvature of the dorsal line (R) may be expressed, generally, as following formula;L/R=B/0.81B-0.22 here, B is the body width.
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