2021 Volume 9 Issue 1 Pages 63-70
The authors intend to clarify the swimming ability of the natural sweetfish (Plecoglossus altivelis altivelis) fingerlings during the initial period of its upstream river migration in the field. The critical swimming speed (CSS) of the natural sweetfish was measured in a small channel with a rectangular cross section under an average cross-sectional water flow velocity of 9–75 cm/s. The body length of the natural sweetfish fingerlings ranged from 5.9cm to 9.9 cm (the mean body length was 7.5 cm, and the number of fishes was 50). The following results were obtained: (1) The CSS, measured for a duration of 60 min, ranged from 19 to 61 cm/s, and a positive correlation was observed between the CSS and the body length. A regression formula between the 60-min CSS and body length was obtained. (2) The ratio of the CSS and the body length was 3.1–8.0 (that is, the distance travelled per second based on the body length), and the mean ratio of the CSS and the body length was 4.7 times (the standard deviation was 1.1).
