抄録
The rheotaxis of fish generally has been understood to depend on the mechanical receptors like the lateral line and cutaneous sensations and, since LYON'S report in 1904, the function of visual sense has been strongly emphasized.
In this study the upstreaming reaction of freshwater fishes was examind under bright and dark conditions, with a rotating water trough devoid of visual objects. Behaviour of eight species of freshwater fishes in the current (17.4cm/s) were compared under three different grades of illumination (4.0, 0.15 and 0.10 Lux) in the darkened laboratory. The results of the experiments are as follows;
Under bright condition (4.0 Lux) fish in the current without visual object showed a weak upstream movement, whereas under dark conditions (0.15 and 0.10 Lux) a vigorous upstream movement was shown. It seemed to be attributed to the compensational reaction by the mechanical receptors which allowed the fish to react positively against the current, without the visual objects under dark conditions. Other experiments at night and in turbid water also were conducted for comparison with the results of observations in the daytime. These data then are consistent with the view on the upstream movement of fish mentioned above.
