EFFECTS OF SUDDEN CHANGE IN SALINITY ON SWIMMING BEHAVIOR OF ANGUILLA JAPONICA

Abstract

 Estuary weir was constructed in the Nagara River to prevent saltwater intrusion, but high-salinity water often stagnates in bottom layer of downstream area of estuary weir. Because of formation of density stratification in downstream area of estuary weir and in fishway, it is assumed that Anguilla japonica suddenly encounter different salinity conditions during migration. In this study, Anguilla japonica acclimated to environmental water of salinity of 3.5% were put into experimental water of different salinities and analyzed swimming behavior of Anguilla japonica. As a result, it was found that Anguilla japonica which acclimated to saltwater of salinity of 3.5% could not follow environmental change when the salinity difference suddenly changed less than 2.0%. Therefore, it is suggested that once Anguilla japonica are acclimated in buffer zone of well-mixed type by using baffle blocks, it can migrate smoothly.