Movement and assemblage of fish in an artificial wetland and canal in a paddy fields area, in eastern Japan

This study, carried out in a paddy fields area in eastern Japan, investigated the timing and patterns of fish movement and assemblage in an artificial wetland and canal. The number of Misgurnus anguillicaudatus and Lefua echigonia immigrating and emigrating between the wetland and the canal accounted for 80–90 % of all the sampled fish. M. anguillicaudatus, L. echigonia, Pseudorasbora parva and Rhynchocypris lagowskii were dominant in the wetland. Immigration of mature M. anguillicaudatus and L. echigonia was detected between late winter and spring. The standard length of the two loach species in the wetland was smaller than that in the canal. These results confirm that wetlands play a role in spawning and nursery for the two species of loaches. The standard length of P. parva in the wetland was smaller than in the canal. This suggests that the wetland was a more suitable spawning and nursery area for this fish species than the canal. L. echigonia used the wetland as a spawning and nursery area, but previous studies reported that the loach did not use paddy fields near the wetland. This could be because the paddy fields were irrigated between June and September and this period did not largely overlap with the fish spawning season. Therefore, we conclude that the conservation and restoration of wetlands, where water is present throughout the year, will contribute toward the preservation of the fish population in a paddy fields area.