1997 年 63 巻 5 号 p. 676-680
The author has developed a device and a method to measure the body length of fish from played back images that reflect laser beams recorded on videotape by an underwater video camera with laser discharge equipment attached, and examined the usefulness of this measuring method through experimentation with dummies in a large water tank on land and in the field. The distances at which the laser spots could be recognized on various colors were, in ascending order, blue, as the lowest, followed by gray, yellow, white, red, and filefish skin; when a distance from the camera exceeds 2.5m, significant errors were observed.
In the field experimentation, the measurement was made using a device for the body length of kokanee salmons, Onchoryncus nerka, coming upstream in an artificial river, and it was compared with that of body length of salmons caught by a trap. Because the mode of both body length distribution coincided, it was confirmed that the usefulness of the measuring method of the body length by the underwater video camera with a laser beam discharge equipment attached. However, its use was limited to conditions of clear water and short distance to fish.