In recent years there has been an increasing activity related to the preservation of living organisms　(biological diversity) worldwide. It is obvious that the long-term trends contributing to this movement include the deterioration of the natural environment in rural villages associated with the introduction of technology solely intended to boost yields along with the urbanization of daily life as a consequence of the remarkable progress in agricultural production technology achieved since World War II. This report describes, firstly the role of paddy field areas as fish habitats compared with natural rivers, secondly the classification of fishes into several groups from the viewpoint of migration.And also it describes the influences of the present paddy field irrigation systems on fish habitat and forecasts future trends in this area.