OPTIMUM DIAMETER OF STUDS IN EEL-LADDER FOR ANGUILLA JAPONICA MIGRATION

Abstract

 Fishways have been constructed to eliminate the obstruction of fish migration by dams and weirs. Fishway research over the years has focused mainly on swimming fish, but in recent years, benthic fish such as eels have also become a target. In Europe and the United States, fishways for eels with brushes and studs on the bottom of fishway have been proposed. However, specifications of studs suitable for migration of eels are not always clear. In this study, diameters of studs on bottom of eel-ladder were varied 12-60 mm, and total length of eels was varied 150-300 mm, to analyze effects of these studs on their migratory behavior. Under experimental conditions, diameter of stud suitable for migration depended on total length of Japanese eel, and 10-20% of total length was found to be appropriate. Future studies to determine whether similar criteria can be applied to Japanese eels with total lengths ranging from less than 150 mm to more than 300 mm are expected to provide partial design guidelines for eel-ladder that facilitate migration of Japanese eels and contribute to conservation of Japanese eels.