Japan is located in the Asian monsoon region. Japan is one of the countries succeeded in modernizing agriculture in the Asian monsoon area. The Land Improvement Act of Japan amended in June 2001 requires agricultural and rural development projects to be harmonized with the environment. It is widely recognized that transforming concrete irrigation and drainage canals into earthen ones, and minimizing the differences in elevation between paddy plots and drainage canals are preferable for the preservation of aquatic animals. However, most paddy fields that have been consolidated using the conventional standard will inevitably remain intact, thus continuing to have substantial influence on the regional environment. Therefore, at least the minimum environmental measures should be effectively performed in the consolidated paddy fields. This book makes clear aquatic animal ecology in a consolidated paddy field, and proposes a variety of selective and gradual approaches in order to preserve the aquatic animals. These measures will enable both agricultural productivity and biodiversity conservation.