EXPERIMENTS ON FISHWAYS FOR FRESH-WATER AMPHIDROMOUS SHRIMPS

Basic conditions of fishways for freshwater amphidromous shrimps, two atyids Caridina japonica and Paratya compressa and a palaemonid Macrob rachium japonicum, which migrate to upstream habitats by walking at ni ght, were studied using an experimental apparatus comprised of ten dis tinct flooring materials. As a result, effective fishway conditions we re defined as follows: three-dimensional mesh structure (0.5 mm in mes h sizes), e.g.,cellular concrete, in the flooring, less than or equal to 50 degrees at the inclination, and less than or equal to 65 cm/s at the surface current velocity in the fishway. A plan for modifying and improving existing fishways and a proposal for preserving populations of amphidromous shrimps above dams are discussed.