“There is rice in the fields, fish in the water.” This sentence inscribed on a stone tablet from the Sukhothai period – a Thai kingdom that flourished 700 years ago – depicts a scene that must have been as idyllic then as it continues to be now. No other combination would seem to be so fundamental and nutritionally complete in the Asian context.
Rice today is grown in 113 countries in the world in a wide range of ecological conditions and water regimes. The cultivation of most rice crops in irrigated, rainfed and deep-water systems offers a suitable environment for fish and other aquatic organisms. Over 90% of the world’s rice, equivalent to approximately 134 million hectares, is grown under these flooded conditions providing not only home to a wide range of aquatic organisms but also offering opportunities for their enhancement and culture.
Production of fish in rice fields is almost as old as the practice of rice or paddy culture itself. Fish culture in paddy fields began in China 2000 years ago and, more recently, practised in Indonesia, Laos, Philippines, Thailand, and Viết Nam. This culture system has very high potential in SE Asia, due to vast areas of irrigated rice fields in the region.
During the time the Viết Nam war (1963-1975), the aquaculture sector was awarded and promoted because of its importance in providing food for people and militarists. In 1965, around 15,000 cooperatives of aquaculture and state-run enterprises were established from the central to localities. Some localities such as Hải Phòng and Thanh Hóa had significant aquaculture development, especially in the field of shrimp farming for exportation. After the Vietnamese reunification, the fisheries sector including aquaculture was identified as a key economic sector of the nation.
There are various cultural practices in Viết Nam’s aquaculture due to its ecological diversification. These include integrated aquaculture systems such as rice-cum-fish, rice-cum-shrimp, mangrove-cum-aquaculture; mono-aquaculture such as semi-intensive, intensive and improved extensive farming of black tiger shrimp, catfishes and marine finfishes; and poly-aquaculture in fresh and marine water bodies.
Shrimp and catfish have been considered as two major aquaculture products of Viết Nam and these products are mostly produced in the Mekong River Delta. The Northern part is dominated by culture systems including freshwater fish ponds, rice-cum-fish and marine cages.
In the unmanageable vast waterlogged rice environments, perennial waterlogged wet rice lands, oxbow type rice fields or flooded river basin rice fields, naturally occurring fishes and prawns enter the field during the monsoon and grow together with the rice crop. The gravid females and young fingerlings enter the field during the wet season when field water overflows and connects neighbouring watercourses to form a vast sheet of water under the rice canopy. The floodwater carries a huge and diversified community of fish, prawn, crabs and other aquatic organisms into the rice paddies.
In the strictest sense, rice-fish farming means the growing of rice and fish together in the same field at the same time. However, it is also taken to include the growing of rice and fish serially one after another within the same field or the growing of rice and fish simultaneously, side by side in separate compartments, using the same water. Fish by no means strictly refers to fin-fish. It means aquatic animals living in rice fields including freshwater prawn, marine shrimp, crayfish, crab, turtle, bivalve, and frog.
One of the oldest fish culture systems in SE Asia can be found in the rice-growing valleys of Northern Viết Nam, where farmers have been growing common carp, originally from China hundreds of years ago. Hundreds of years of this management have produced a thin variety of common carp more suited to shallow local rice field conditions.
In the traditional rice-fish farming system, farmers use an existing or dugout pond adjoining to their rice field and make provisions to improve the collection and capture of wild fish without any management practice. In the scientific method of rice-fish culture, proper fish pond preparation, selective stocking of different species of fish, the addition of inputs like feed, fertilizer along with other post stocking management and harvesting of the marketable size of fish after gathering paddy crop are undertaken.
Rice Harvest Season
Farmers practised both simultaneous and rotational systems of culture depending on the prevailing conditions. Economic analysis is made only on the simultaneous system in which fish and rice are cultured in the same field, with rice as the main crop. Preparation of the paddy fields starts in April-May and cropping of locally available variety of rice is completed within June-July. As the water level increases with the onset of monsoon, the farmers release fingerlings at a very high density of about 20,000-25,000 ha. Fish stay in the paddy fields up to December and start migrating to the actual fish pond as the water level goes down in the paddy field. Paddy is harvested during November-December followed by the harvest of fish in January-February. Farmers use organic and inorganic fertilizers during paddy field preparation.
The real and potential impact of rice-fish farming in terms of improved income and improved nutrition is significant but generally underestimated and undervalued. Hidden benefits of rice-fish farming such as risk reduction through diversification of the farming system may have a strong attraction to many farmers and their families. Fish can be sold directly or may reduce the dependence of families on other livestock which can then be traded for income. Also, fish from the rice fields may not be sold but the production may be used to feed relatives and those who assist in rice harvesting, a benefit which could almost be considered essential in families with a labour shortage. Rice-cum-fish culture not only produces fish but also increases paddy production by up to 14%.
Species of fish
The fish to be stocked in rice fields should be capable of tolerating a harsh environment characterized by shallow water, high (up to 40°C ) and variable temperatures (range of 10°C in one day), low oxygen levels and high turbidity. Fast growth is also mentioned as a desirable characteristic so that the fish could attain marketable size when the rice is ready for harvest. With such adverse environmental conditions that a fish could tolerate, it would seem that very few of the commercially valuable species are hardy enough to qualify.
This, however, is not the case. A review of rice-fish farming practices around the world reveals that practically all the major freshwater species now being farmed, including 37 finfish species (from 16 families) and seven crustaceans (from four families). Molluscs, primarily snails and some freshwater clams are often harvested from rice fields, but there is little information that these are intentionally stocked. The same is true with frogs and freshwater turtles. Two groups of fish stand out in rice-fish farming: cyprinids and tilapias. The cyprinids, particularly the common carp and the Carassius (crucian carps) have the longest documented history. The common carp has figured prominently since ancient times up to the present and is raised in rice fields in more countries than the other species.
In Viết Nam, the farmers also stock rice paddy fields with silver barb and Nile tilapia. Fish-rice culture is a means to increase fish production and to improve the paddy field’s ecology. The system has been proven to be advantageous in fingerling production in floating net cages.
Much has been said about the mutualism of fish and rice. Mutualism implies beneficial effects on each other. Rice acts as a nitrogen sink and helps reduce the ammonia that may be released by the fish and in doing so helps make the water cleaner for the fish.
In summary, rice fields where fish are stocked will likely have a higher yield because the rice field will have fewer weeds and fewer stem borers. Fewer weeds to compete with the rice for soil nutrients and fewer pests cannot but contribute to the production of more and bigger grains, and a reduced occurrence of unfilled grains. In short, rice fields with fish have healthier rice plants than those without fish.
One reason why farmers can no longer catch fish in their rice fields like they used to, especially if irrigation comes from river water, is the increased use of pesticides. The use of chemicals is often cited as one of the major constraints in the popularization of rice-fish farming. Yet stocking fish in rice fields actually reduces pest infestation, and thus also reduces if not eliminates the need for the application of herbicides and insecticides and particularly molluscicides where snail predatory fish are cultivated. The practical and economic advantages of using fish instead of chemicals are often obvious.
Often overlooked is the fact that fish in the rice fields can reduce the use of chemical pesticides. Even though some pesticides are considered safe to use in rice-fish farming due to their low toxicity, low tendency to bioaccumulation, and short half-life, pesticides are still poisons and may be carcinogenic or harmful in other ways. Their use and misuse is a serious public health issue that may become more serious than mosquitoes and snails. Fish are potentially a good herbicide and insecticide and stocking can greatly reduce, if not eliminate, the need for using chemical pesticides. The presence of fish discourages farmers from applying pesticides.
The effectiveness of fish as a bio-control agent depends on how well they are distributed within a rice field. If fish stay mostly in the pond refuge then they cannot be effective in controlling rice pests.
By 2050, the world’s population is expected to reach 10 billion, mainly driven by growth in poor and densely populated regions of Asia and Africa, whose livelihood is highly dependent on rice for food and socio-economic advancement. There is a combination of things that have worked to conspire against the farmers. Growing population means there’s a need to increase production to assure food supply for the world.
Along with a surging world population, global rice demand is projected to increase by up to 25% between 2010 and 2030 to 550 million tonnes a year. About two-thirds of this demand will come from Asia.
There are of course other factors such as safety for humans and livestock and the relative intended result are also important considerations, which, at any rate, apply whether or not fish are cultured with rice.
There are four major groups of pesticides used in rice fields: herbicides, insecticides, fungicides and molluscicides. Herbicides are considered the least toxic and insecticides generally the most toxic to humans. Current changes in rice culture including high labour costs and increasing nitrogen fertilization appear to be resulting in increased herbicide and fungicide use, respectively. Several herbicides and fungicides are known to have high non-target toxicities and therefore need to be critically examined. Rice-fish farmers tend to avoid pesticides, mainly because the risk of killing the fish is high particularly when pesticides with high fish toxicity are applied. The use of non-toxic or low-toxic compounds is viewed cautiously as well since even though the consumption of contaminated fish is not likely to cause immediate death or illness it may result in residues and bio-accumulation of these so-called “safe” pesticides.
Global warming, sea-level rise, increased ultraviolet radiation and even availability of water are all expected to have an adverse impact on rice production and leading to a significant loss in rice yield. Climate change poses a threat to food production. But at the same time, agriculture itself is a sector that generates high levels of carbon emissions.
First, the experts agree that to unlock the full potential of rice production and overcome the threats, all stakeholders must collaborate to find innovative solutions toward a sustainable and equitable global rice sector that will transform lives for the better.
We need to strengthen partnerships and alliances with rice sector actors across countries, borders, and sectors of society. The partnership has to seek to improve the genetic outcomes of breeding programs, breeding technologies, encourage sustainable rice cultivation and develop new rice varieties that deliver higher yields and are more resilient against biotic and abiotic stresses.
There is clear evidence that rice-fish culture is a viable, environment-friendly, low-cost, low-risk additional economic activity with multiple benefits including increased incomes and greater availability of fish to the rural farming community. The poor fish farmers don’t have sufficient funds to practice rice-fish farming with all the necessary inputs and dyke preparation.
To harness this potential, the government should address the constraints by financial assistance to encourage the poor farmers to adopt the rice-fish culture. Short-term, low-interest loans, primarily to support earthwork and subsidy to overcome the loss due to floods should be made available to farmers.
Last, in order to popularize rice-fish culture, the concept should become part of the agricultural system rather than the fisheries system. The fisheries agencies will need to put further efforts in the establishment of a viable national fish seed production and distribution system operated by the private sector so that fingerlings of the desired species are readily available to the farmers. Only then can more fish be found in the rice fields.