MIGRATION CHARACTERISTICS OF YOUNG EEL ON SLOPE EEL LADDER WITH STRIP ROUGHNESS

Abstract

 It is becoming clear that cylindrical protrusions are effective for eel migration. However, it is feared that if nylon tape debris or flexible fragments of long vegetation flow into the fishway, they may become entangled in the cylindrical protrusions and block the gap, making it difficult for eels to migrate upstream. In this study, we proposed a fishway for eels with strip roughness at the bottom. The roughness interval was varied from 50 to 200 mm, and the flow rate was varied from 140 to 540 ml/s. The roughness interval was determined to be appropriate for a 200mm long Anguilla japonica. As a result, a roughness interval of 100 mm, which is 0.5 times the total length, was found to be effective. This was attributed to the fact that the eels behaved differently in climbing over the strip roughness as the spacing changed. It was found that the eels could easily insert their bodies into the grooves of the roughness when the spacing was 0.5 times the total length, and the roughness could be used as an object of the migration reaction force, leading to the improvement of the migration rate. On the other hand, when the spacing was 0.25 times the total length, it is difficult to insert their bodies between the roughness, and when the spacing is more than 0.75 times the total length, it is difficult for the tail to contact the downstream rouguness, resulting in a lower migration rate.