EFFECTS OF BOULDERS INTERVAL IN STREAMWISE DIRECTION OVER OPEN CHANNEL BED ON SWIMMING BEHAVIOR OF Opsariichthys platypus

It is important to keep suitable area by boulders to make rest area for fish. In this study, swimming behavior of Opsariichthys platypus in open channel were compared with change of boulders interval in streamwise direction over open channel bed. Swimming behaviors of Opsariichthys platypus were obtained with the aid of two sets of digital video cameras. It was found that swimming of Opsariichthys platypus was stagnant remarkably in cases where the boulders interval in downstream direction was narrow. It is because that there are more low velocity spaces in this case compared with cases where the boulders interval in downstream direction is wide.