In many countries and especially in China, it is a “political crop,” as well, because rice is one of the most important crops for national food security. Rice is the main ingredient of daily diets in China, providing roughly half of the grain consumed by Chinese people. Rice–fish farming systems should be evaluated to determine what ecosystem functions they generate and whether they are worthwhile endeavors for farmers. The stability of rice yields in rice monoculture and rice–fish co-culture was compared through both a farmers’ field survey and a field experiment. Compared to intensive aquaculture farms, traditional rice–fish co-culture farms are smaller and produce lower fish yields. Rice–fish farming systems are thought to be globally important in terms of three environmental issues: climate change, shared water, and biodiversity. Rice plants can provide a better environment for fish by cleaning field water and providing shade during the hot summer season.