Rice-fish system

A rice-fish system is a polyculture practice that integrates rice agriculture with aquaculture, most commonly with freshwater fish. This practice is highly valued as it was one of the first to be considered as a “Globally Important Agricultural Heritage System” according to FAO-GEF (Global Environment Facility). It is based on a mutually beneficial symbiotic relationship between rice and fish that is developed when introduced into the same ecosystem. Many benefits in various spheres come with these systems.

History

The simultaneous cultivation of rice and fish is thought to be over 2,000 years old. Ancient clay models of rice fields, containing miniature models of fish such as the common carp, have been found in Han dynasty tombs in China. The system originated somewhere in continental Asia such as in India, Thailand, northern Vietnam and southern China. The practice likely started in China since they were early practitioners of aquaculture.

Archaeological evidence suggests that common carp were probably among the first fish used in rice-fish systems. Wei dynasty records from 220 to 265 AD mention that "a small fish with yellow scales and a red tail, grown in the rice fields of Pi County northeast of Chengdu, Sichuan Province, can be used for making sauce". Liu Xun wrote the first descriptions of the system, with texts written during 900 AD during the Tang dynasty. Rice-fish systems may have evolved from pond culture in China; one theory proposes that the practice started when farmers decided to place excess fry in their ponds and found the results beneficial.

It is possible that the practice developed independently from China in other Asian countries. It appears to have spread from India to neighbouring Asian countries over 1500 years ago. The practice slowly gained popularity among farmers, and by the mid-1900s, over 28 countries on all continents except Antarctica used rice-fish systems. Historically, the common carp and the Mozambique tilapia (Oreochromis mossambicus) were the most commonly grown fish. As the practice spread throughout the world, new species were adopted. For example, Malaysia introduced the snakeskin gourami (Trichogaster pectoralis) and Egypt uses the Nile tilapia (Oreochromis niloticus).

An early study, in Jiangsu Province in 1935, found that growing black carp (Mylopharyngodon piceus), grass carp, silver carp, bighead carp (Aristichthys nobilis) and common carp together with rice was beneficial.

Rice-fish systems were traditionally low maintenance, growing additional animal protein alongside the staple food, rice. From the 1980s on, Chinese systems developed rapidly with new species such as the Chinese mitten crab, the red swamp crayfish, and softshell turtles. The space used for fish-rice systems in China grew from 441,027 hectares (1,089,800 acres) to 853,150 hectares (2,108,200 acres) and the production increased dramatically, going from 36,330 tonnes (35,760 long tons; 40,050 short tons) to 206,915 tonnes (203,647 long tons; 228,085 short tons) between 1983 and 1994.

Principle

Design of a rice-fish system with channels.
A: Before harvest B: After harvest C: Re-flooding

Rice-fish systems are based upon the Rice-Fish Symbiosis theory. Both rice (a semiaquatic wetland crop) and fish are grown in the same aquatic ecosystem and both benefit from this, creating a mutualistic relationship. The principle has evolved through the years and major technological advances allowed for the popularisation of the practice. A notable improvement was the addition of channels in the previously flat rice fields that allowed for the fish to continue growing even during rice harvest and dry seasons.

Before creating the rice field, the field is treated with 4.5–5.25 tonnes per hectare (2.0–2.3 short ton/acre) of organic manure. Organic manure is also applied during the main growing season, with about 1.5 tonnes per hectare (0.7 short ton/acre) of organic manure applied every 15 days. Doing this provides nutrients for rice and the added cultures of plankton and benthos that are used to feed the fish. During the main growing season, supplementary feeds complement the plankton and benthos culture and are used once or twice a day. The supplementary feeds include fish meal, soybean cake, rice bran and wheat bran. Fish is stocked at a rate between 0.25 and 1 per square metre (1,000–4,000/acre).

Unwanted fish or invasive species can threaten the symbiotic relationship between rice and fish and therefore threaten the food production. For example, in the integrated Rice-Swamp Loach Aquaculture Model, catfish, snakeheads (Channa argus) and paddy eels (Monopterus albus) are considered as unwanted species. Predatory birds can also be considered a threat: adding nets to the rice fields can prevent these birds from eating the wanted fish.

Rice-fish systems are only one type of integrated rice-field system: 19 other models exist, for example rice-crayfish, rice-crab and rice-turtle.

Rice-fish symbiosis

Rice and fish form a mutualistic symbiosis: they both benefit from growing together. The rice provides the fish with shelter and shade and a reduced water temperature, along with herbivorous insects and other small animals that feed on the rice. Rice benefits from nitrogenous waste from the fish, while the fish reduce insect pests such as brown planthoppers, diseases such as sheath blight of rice, and weeds. By controlling weeds, competition for nutrients is decreased. CO₂ released by the fish may be used in photosynthesis by the rice.

The constant fish movements allow for the loosening of the surface soil which can:

• Improve oxygen levels by increasing the amount of dissolved oxygen. Consequently, the activity of microorganisms is increased and they generate more usable nutrients, which will allow an increased nutrient uptake for the rice.

• Increase mineralization of the organic matter.
• Optimization of nutrient release in the soil.
• Promote fertilizer decomposition and therefore fertilizer effectiveness.
• Better root development of the rice.

Soil fertility is improved by the integration of fish, whose manure is a fertilizer recycling organic matter, nitrogen, phosphorus and potassium. The inclusion of fish in rice-fields helps to maintain soil health, biodiversity, and productivity.

The aquatic diversity in rice-fish systems includes plankton (both phytoplankton and zooplankton), soil benthic fauna and microbial populations that all play a role in the enhanced soil fertility and the sustainability of production. However, benthic communities may be disturbed by constant grazing from the fish.

Benefits

Economic

Net gains vary between and within countries. Overall, integrated rice-fish fields have a positive impact on net returns. In Bangladesh, net returns are over 50% greater than in rice monocultures. In China, the net return by region is between 45 and 270% greater. A case of loss in net returns was found in Thailand with only 80% of the profitability of rice monocultures. This might be caused by the initial investment needed when starting the system. The need for manual labour decreases, since fish control weeds and pests. Farm income rises by over 23%. The use of rice-fish systems has resulted in an increase in rice yields and productivity from 6.7 tons to 7.5 tons of rice per hectare and simultaneously also from 0.75 tons to 2.25 tons of fish per hectare. The landscapes created by rice-fish systems form a possible tourist attraction, as it creates a distinctive landscape.

Public Health

In 1981, the Health Commission of China recognised integrated rice fields as a possible measure to decrease the population of mosquitoes, which carry diseases such as malaria and dengue fever. The larvae density is reduced in integrated rice fields since freshwater fishes routinely prey on the larvae. Cases of malaria drastically decreased in a highly endemic area, going from 16.5% to 0.2% cases in only five years. Rice-fish systems may decrease the number of snails, known to carry trematodes that in turn cause schistosomiasis. Farmers' diets may improve with the addition of fish protein.

Environmental

As fish control pests and weeds, fewer chemicals (such as pesticides and herbicides) are used, reducing the release of these agricultural chemicals into the environment. In turn, biodiversity is increased. Rice-fish systems can reduce methane emissions compared to rice monoculture.

Applications

Developing countries

Rice-fish systems are being exported to less developed countries with the FAO/China Trust fund. About 80 Chinese rice-fish experts were sent to underdeveloped countries in diverse regions of the world such as certain African countries, other parts of Asia and in the South Pacific to implement the rice-fish systems and their benefits as well as share their agriculture knowledge. For example, the China-Nigeria South-South Cooperation programme integrated over 10,000 hectares of rice-fish fields in Nigeria, which has allowed for the production of rice and tilapia to almost double.

Climate change

Climate change threatens global food production as it creates numerous changes to regional weather, such as higher temperatures, heavy rainfall, and storms. These changes may cause outbreaks of pests with, for example, an increase in the number of plant hoppers and stem borers. Rice-fish systems should be beneficial in future climates because they have higher reliability and stability than rice monoculture.

See also

• Rice-duck farming