A Flume for Behaviour Studies of Marine Fish

A flume is described for producing currents of sea water for behaviour studies of marine fish. Its cross-section is 30 cm. wide × 32·5 cm. deep and the observation length is 550 cm. Velocity and depth of water can be finely controlled and the maximum velocity in the level position is 69 cm./sec. with a depth of 10·8 cm. Maximum depth is 29 cm. By tilting the flume the maximum velocity can be increased to 132·5 cm./sec. at a depth of 5·5 cm. with a maximum gradient of 1 in 40. An instrument for measuring current velocity by an optical technique is also described. Its range is 0·8−240 cm./sec. with an accuracy of ± 1% over the range 0·8−8 cm./sec. in its lowest gear and ± 0·5% from 2 to 240 cm./sec. in the higher gears.