Fish culture in rice fields provides the means for the contemporaneous production of grain and animal protein on the same piece of land (Schuster, 1955) and is by far the most expanded mixed crop-fish farming system in the world (about 2 Mha). No other combination would seem to be so fundamental and nutritionally complete in the Asian and other context featured with water availability.

• Diversity. Nutritional benefits and lowered production risk may provide strong motivation for rice farmers to diversify, and rice-fish farming can be both socially and environmentally profitable (Halwart, 1999). Production diversification enhances biodiversity when agrochemical use is avoided.

• Coherence. Biodiversity is structured in a self-sustaining biocenosys, i.e. a self-sufficient community of naturally occurring organisms occupying and interacting within a specific biotope, which makes the rice field system more balanced and internally coherent. With fish removing weeds and reducing the insect pest population to tolerable levels, poisoning of the water and soil may be curtailed. Moreover, particularly in more remote areas, fish and other aquatic organisms from rice fields provide a very important component of the daily diet, hence the term “rice-fish societies” (Demaine and Halwart, 2001). Input analyses in Bangladesh, the Philippines and Vietnam consistently showed an increase from 10 to as high as 234 percent in the overall labour requirement when fish were raised in rice fields (Halwart and Gupta, 2004).

• Connectedness. The rice-fish culture required an estimated 26 percent more water than rice monoculture, which is a concern in water-scarce regions (Sevilleja et al., 1992). Field surveys carried out in China and Indonesia found rice-fish systems able to make drastic reductions in the density of mosquitoes carrying malaria and dengue fever (Wang and Ni, 1995; Nalim, 1994). There are also examples of beneficial impacts of rice-fish systems on social connectedness through time-sharing of rice fields, where landless tenants and fish breeders are allowed to use the rice fields for fish culture during the fallow season (Koesoemadinata and Costa-Pierce 1992; Fagi et al., 1992). The adoption of rice-fish systems can result in job creation and diversification, such as diking, making and renting nets and other accessories such as pumps and oxygen tanks, repairing pumps, and harvesting, packing and transporting of fingerlings (Halwart and Gupta, 2004). • Efficiency. Studies of rice-fish systems in Bangladesh, China, Indonesia, the Philippines and Vietnam reported increases of net returns ranging from 27 to 270 percent above those from rice monoculture (Gupta et al., 1998; Yan et al., 1995a; Purba, 1998; Sevilleja, 1992; Mai et al., 1992). In Thailand, profitability in the rice-fish fields was found to be only 80 percent of rice monoculture profitability (Thongpan et al., 1992).

• Resilience. Diversification of products makes the fish-crop systems more resilient to price changes.

Capacity for a green economy. Over 90 percent of the world’s rice, equivalent to approximately 134 million hectares, is grown under flooded conditions, providing not only home to a wide range of aquatic organisms, but also offering opportunities for their enhancement and culture (Halwart and Gupta, 2004). Although most countries do not have separate statistics on rice-fish farming areas or rice and fish yields in such areas, speculations indicate that the potential impact of conversion from rice monoculture to mixed systems is tremendous, also at the macro-economic level. For example, if 5 percent of the irrigated rice lands in the Philippines were stocked with fish, the production would increase by 29 000 tonnes and provide 5 900 tonnes of protein (Ahmed et al., 1992). Cai et al. (1995a) estimated that if 10 percent of the rice fields south of the Huai He River, China, were used, the commercial fish yield would be 346 000 tonnes with a yield of 300 kg/ha, and five billion full-size fingerlings. In Asia, the main problem under 2050 scenarios will be land scarcity (particularly in South Asia) and the consequent need for high levels of intensification. Expansion of cropped land can only occur in some areas (at the expense of forests or pastures) but not in South Asia. Intensification would increase the risk of input price increase and water availability under extreme climate events and pollution. Therefore, it would be helpful to design new or encourage existing intensive farming systems to reduce the risk of input dependency and climate variability. The rice/fish system is an example of a natural resource management option with low external input that simultaneously meets the need of agricultural intensification and the need to decrease pollution. However, it requires a considerable amount of water and should be integrated at regional level with alternative water-saving options, such as sustainable rice intensification.