Review of Rice–Fish–Duck Symbiosis System in China—One of the Globally Important Ingenious Agricultural Heritage Systems (GIAHS)

Abstract

The Chinese rice–fish–duck symbiosis system is one of the globally important agricultural heritage systems, with a history of nearly a thousand years. It embodies the wisdom of the Chinese ancestors and has huge comprehensive value, which has extremely important references for the sustainable development of agriculture. The technological core for the rice–fish–duck symbiosis system lies in the selection of rice, fish, and duck varieties and the coupling of agricultural operation time. In the process of modern agriculture, many varieties with high comprehensive benefits have also been applied to the rice–fish–duck system, and the rice–fish–duck model has been further developed. What is worrying is that the transfer of rural labor, the promotion of modern agricultural technology, the low degree of marketization and industrialization, the weakening of cultural awareness, and the change in climate have posed huge threats and challenges to the traditional Chinese rice–fish–duck system. The protection and development of the system are urgently needed. Therefore, we recommend delimiting active protection areas, establishing scientific research bases, improving relevant systems, developing rural tourism markets, and innovating farming technology, which also provide guidance for protecting and developing other agricultural cultural heritages.

1. Introduction

China is an agricultural country where farming civilization has occupied a very important position in its development for thousands of years. People accumulated a lot of production knowledge and experience in farming, which has become an important agricultural cultural heritage in the industrial age. In the mountains of Congjiang county in the southeast of Guizhou, there is a concentrated settlement of Dong’s people, which is called “Dongxiang”. According to the growth characteristics of rice, fish, and ducks, the Dong’s people skillfully weave the three species that are originally compatible with each other into an artificial system so that rice, fish, and ducks can coexist harmoniously, thus forming a typical traditional ecological agricultural system—rice–fish–duck system [1] (Figure 1). The rice–fish–duck system is a classic agronomy of traditional Chinese agriculture and has become the first batch of important agricultural cultural heritage in China [2].

In the rice–fish–duck system, multiple symbiotic relationships have been formed between organisms (Figure 2). Rice is the main producer and it provides shade and shelter for fish and ducks. Fish and ducks are the main consumer. They prey on pests and weeds, therefore, controlling diseases, pests, and weeds in the rice paddy. They also stimulate rice roots and increase dissolved oxygen to promote rice growth. At the same time, the manure of fish and ducks improves soil fertility, and the rice absorbs these organic fertilizers to purify the water in turn. Moreover, the symbiosis of rice, fish, and duck improves the species diversity of the system. Thus, a complex food chain network is established, in which energy, water, and fertilizer utilization efficiency is high, and which has greater stability and the ability to resist external shocks [3].

This system of rice–fish–duck symbiosis adopts the agricultural production method of “planting one season of rice, stocking a group of fish, and raising a group of ducks”, providing local residents with abundant agricultural and sideline products. The rice–fish–duck model has multiple uses in one field, producing both vegetable protein and animal protein in the same production process, providing a sufficient source of nutrition for local residents. This system can effectively prevent and control diseases, pests, and weeds through internal adjustment, avoid the pollution of chemical fertilizers and pesticides, and ensure food safety and personal health [3].

A large number of studies has shown that the rice–fish–duck system has obvious ecological benefits [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21], rich economic benefits [22,23,24,25,26,27,28,29], and extensive social benefits [30,31,32,33,34,35]. However, under the impact of modern culture, the traditional rice–fish–duck system also faces many threats and challenges [36,37,38,39,40,41,42,43], and the protection and development of agricultural cultural heritage is an urgent need.

Based on this, this paper systematically reviews the comprehensive functions and technologies of the rice–fish–duck system, which has extremely important references for the sustainable development of agriculture, especially in today’s world with serious environmental pollution, low agricultural economic benefits, and backward rural development. At the same time, the threats and challenges faced by the rice–fish–duck system, as well as the ways of protection and development, are systematically elaborated, which is expected to provide guidance for protecting and developing agricultural cultural heritage.

2. The Literature Collection

We searched journal papers and dissertations on China National Knowledge Infrastructure with rice, fish, and duck as the subject words and retrieved 119 pieces of literature from 1989 to 2022. At the same time, we searched for articles and reviews on Web of Science with rice, fish, and duck as the subject words and retrieved 90 pieces of literature from 1963 to 2023. By analyzing the abstract and the main contents of the literature, sixty pieces of literature related to the rice–fish–duck symbiosis system or the GIAHS were screened, including fifty-two pieces of literature from China National Knowledge Infrastructure and eight pieces of literature from Web of Science.

3. Rice–Fish–Duck Symbiosis System as a Globally Important Agricultural Heritage Systems (GIAHS)

The GIAHS have been created by FAO in partnership with the Global Environment Fund (GEF), the United Nations University’s People Land Management and Environment Change (PLEC) Project, and UNESCO’s Man and the Biosphere (MAB) and World Heritage Programs [44]. The FAO defines the GIAHS as “the unique land use systems and agricultural landscapes formed by the long-term co-evolution and dynamic adaptation of the countryside and its environment, which are rich in biodiversity, and can meet the needs of local social, economic and cultural development, and is conducive to promoting regional sustainable development” [45]. So far, the FAO has identified 67 systems and heritage sites in 23 countries or regions, of which China ranks first with 18 [46].

In June 2011, the FAO listed Dong’s rice–fish–duck system in Congjiang county of the Guizhou province as a pilot project for the protection of the world’s important agricultural cultural heritage, and Congjiang has become China’s fourth protection site after Qingtian county in Zhejiang, Honghe prefecture in Yunnan, and Wannian county in Jiangxi [1]. According to historical records, the history of Dong’s rice–fish–duck co-production in Congjiang can be traced back to the Ming Dynasty, at least. However, it is inferred from the local oral history data, such as “Ancient Songs”, and legends that it has a history of nearly a thousand years [3].

4. Significant Ecological Benefits

4.1. Control Rice Diseases, Pests, and Weeds

After ducks and fish enter the paddy field, the pecking effect of ducks and the swallowing effect of fish are worked. On the one hand, part of the sclerotia of pathogens can be removed, thereby reducing the source of bacteria. On the other hand, most of the germinated mycelium can be wounded and atrophied, thereby losing the ability to infect. In addition, ducks and fish peck the diseased rice leaves and field weeds, reducing the pathogenic bacteria and improving field ventilation and light transmission that are not conducive to the spread of bacteria [4]. Zheng Yonghua et al. [5] found that the rice–fish–duck symbiosis system significantly reduced the incidence index of rice sheath blight. Liu Xiaoyan et al. [6] also found that the diseased plant rate at the peak of the sheath blight in the rice–duck–fish symbiotic ecosystem was 16.07%, which was 60.30% lower than that of rice monocropping.

Fish and ducks can directly devour the pests on the water surface and the lower even middle parts of the rice plants. They also shake the rice plants, causing the pests inhabiting the upper part of the rice plants to fall into the water [4]. At the same time, the natural growth rate of spiders in the rice–fish–duck system is 54% higher than that of rice monoculture, and spiders, as natural enemies of rice field pests, play an important role in the prevention and control of pests [7]. Wang Ying et al. [8] and Zheng Yonghua et al. [5] showed that, compared with rice monoculture, the rice–fish symbiosis system, and rice–duck symbiosis system, the rice–fish–duck system had the best pests control effect and significantly reduced the population density of pests such as rice planthoppers, borers, and budworm. Liang Yi et al. [9] also found that the population density of rice planthoppers in the rice–fish–duck co-cropping paddy field was 274% lower than that in the rice monocropping field. Xu Fang [10] also showed that, compared with the rice–fish symbiosis, the rice–fish–duck system significantly reduced the number of rice planthoppers and borers, and at the same time significantly increased the number of natural enemies (spiders).

Fish and ducks’ feeding, root digging, trampling, and water mixing have obvious control effects on field weeds. Wang Ying et al. [8] showed that compared with rice monoculture, rice–fish symbiosis, and rice–duck symbiosis, the rice–fish–duck system significantly reduced the dry matter mass of weeds per unit area. Zhang Dan et al. [11] and Nayak et al. [12] also found that the rice–fish–duck system significantly reduced the occurrence density and biomass of weeds in the field, and the overall weed suppression effect was significantly better than that of rice monoculture, rice–duck symbiosis, and rice–fish symbiosis. In the rice–fish–duck system, the species richness index of weeds (Simpson) and the diversity index (Shannon) decreased significantly, but the community evenness index (Pielou) increased, indicating that the weed community composition was highly diverse and the previously dominant weed species decreased (

Table 1. Status of rice diseases, pests, and weeds in different rice cropping systems.

Treatment	Rice Sheath Blight (%)	Pests (Number/m2)	Dry Weight of Weeds (g/m2)	Quantity of Weeds (Number/m2)
Rice monoculture	37.70–67.56	72.50–97.90	189.00–200.50	53.38–94.54
Rice–fish farming	4.90–42.00	45.30–67.55	9.00–10.20	10.44–41.08
Rice–duck farming	2.50	15.20–18.00	20.00–51.00	\
Rice–fish–duck farming	1.40–16.07	9.00–12.15	0.10–0.50	7.80–18.30
References	Zheng Yonghua et al.; Liu, Xiaoyan et al. [5,6]	Wang Ying et al. [8]	Wang Ying et al. [8]	Zhang Dan et al. [11]

).

4.2. Increase Soil Fertility

Fish and ducks stir the water and soil in the paddy fields, playing the role of changing the community structure of soil microorganisms [13] and accelerating the turnover of soil nutrients. At the same time, excrement of fish and ducks supplements the soil nutrient pool to a certain extent. Liang Yi et al. [9] showed that the total amount of nitrogen, phosphorus, potassium, and organic matter in the soil of the rice–fish–duck compound model was increased by 20.1%, 57.3%, 17.3%, and 18.9%, respectively, compared with the single-cropping paddy field. Nayak et al. [14] also found that the content of soil organic matter, total nitrogen, and available nitrogen, phosphorus, and potassium in the rice–fish–duck co-cropping system was significantly higher than that in the conventional rice system.

4.3. Improve the Biodiversity of Paddy Fields

The intervention of fish and ducks makes up for the missing ecological niche in the traditional rice farming system, effectively controls the pests and diseases in the field, reduces the application of pesticides and herbicides, and thus greatly enhances the diversity of the rice field ecosystem [6,7,8]. In the rice–fish–duck system, a variety of organisms co-exist and occupy different ecological niches: plankton, floating leaf plants (Potamogeton distinctus, lemna), and floating plants (Salvinia natans, Azolla imbricata) are distributed on the surface water. Rice, ducks, insects, etc., live in the upper water layer. Fish are mainly active in the middle water layer. The bottom water layer gathers benthic animals (field snails, eels, loach, rhizomes of emergent plants, and submerged plant black algae). In this way, dozens of organisms form a complex food web around rice, fish, and ducks, which enhances the stability of the system [1].

4.4. Function of “Invisible Reservoir”

In order to meet the normal living needs of fish and ducks, the depth of the water layer for the rice–fish–duck system is usually more than 30 cm. Therefore, this rice field has a huge potential for water resources reserves [4]. In the continuous dry season, a large amount of water resources stored in rice fields can meet the normal needs for rice and can even be transported to other dry rice fields, which is equivalent to a micro-reservoir [15]. Therefore, the rice–fish–duck system provides valuable enlightenment for the development of water-saving agriculture in today’s uneven precipitation distribution at the seasonal and regional scales.

4.5. Reduce Agricultural Non-Point Source Pollution

Agricultural non-point source pollution caused by the excessive use of pesticides and chemical fertilizers, livestock breeding wastewater, and direct discharge of domestic sewage in rural and urban areas has become the main reason for the deterioration of China’s ecological environment. The traditional rice–fish–duck agricultural ecosystem uses resources economically and efficiently, reduces the use of chemical fertilizers, pesticides, and herbicides, improves the water quality of farmland, and avoids the destruction of biodiversity caused by the application of chemical fertilizers and pesticides through a harmonious internal structure. The harmless and resourceful use of materials not only reduces external input, but also eliminates the cost of environmental pollution control, which alleviates the inevitable ecological side effects in the process of agricultural modernization. It also has a great impact on the prevention and control of agricultural non-point source pollution [16,17].

4.6. Reduce Greenhouse Gas Emissions

Carbon dioxide, methane, and nitrous oxide are the three major greenhouse gases in the atmosphere, and their increasing concentrations are the direct cause of global warming. Rice fields are the main agricultural source of methane emission. Methane emission from rice fields is a comprehensive manifestation of methane production and oxidation [18,19]. In the rice–fish–duck system, the activities of fish and ducks agitated the water, loosened the soil, significantly increased the dissolved oxygen content in the water [8], greatly reduced the content of soil reductants, and increased the redox potential. Therefore, the emission flux of methane is reduced, and the control effect on the peak period of methane emission from the paddy field is the most obvious [20]. Nayak et al. [21] also found that the rice–fish–duck symbiosis system has a significant mitigation effect on greenhouse gas emissions through a meta-analysis of China’s agricultural management measures. Therefore, under the background of global warming, the rice–fish–duck system has important practical significance.

5. Economic Benefits

The rice–fish–duck co-breeding model organically combines rice (the largest primary producer) with fish and ducks (the largest consumers) to form an ecosystem with fish-to-rice, duck-to-rice, and duck-to-fish symbiosis, mutual benefit, and mutual promotion. It improves the overall function of the rice field ecosystem, plays a role in the integration of system functions, and improves the overall productivity of the rice field. From the viewpoint of energy science, fish and ducks can make full use of the material and energy of the rice field ecosystem and increase the utilization rate of luminous energy. In addition, fish and ducks recycle a large amount of dispersed energy (weeds) and lost energy (plankton, insects, etc.) to the energy cycle of the ecosystem, forming a virtuous circle [22].

On the one hand, fish and ducks create a good paddy environment for rice by preventing and controlling field pests and weeds and increasing paddy fertility, improving the growth and development of rice [23,24], which is beneficial to the improvement of rice quality. On the other hand, the breeding of fish and ducks increases the types and quantities of rice field products [25,26]. Moreover, fish and ducks have higher economic value than rice. Therefore, compared with conventional rice monoculture, the economic benefits of the rice–fish–duck system are significantly improved. Che Zhengming et al. [28] found that the economic benefits of the rice–fish–duck symbiosis model increased by 241.9% compared with rice monoculture. Xu Fang [10] found that the economic benefits of the rice–fish–duck symbiosis model increased by 17.2% compared with the rice–fish symbiosis model. Meng Xiangjie et al. [47] showed that the rice–fish–duck model also has higher economic benefits than the rice–fish model and the rice–duck model, with an increase in income by 32.9% and 229.0%, respectively. We also investigated the economic benefits of the rice–fish–duck farming in the Hunan province, and found that it increased the economic benefits by 163.6% compared with rice monoculture (

Table 2. Comparison of economic benefits between rice monoculture and rice–fish–duck farming (CNY/ha).

	Input					Output			Net Income
	Rice Seed	Fertilizer	Mechanics	Fry and Ducklings	Labor Force	Rice	Fish	Duck
Rice monoculture	900	1500	5400	0	6750	19,500	0	0	4950
Rice–fish–duck farming	900	900	5400	27,000	11,250	19,500	15,000	24,000	13,050

Note: The average yield of rice under monoculture is 7500 kg/ha, and that of rice–fish–duck symbiosis system is 4875 kg/ha. The average price of monoculture rice is 2.6 CNY/kg, and that of rice–fish–duck symbiosis system is 4 CNY/kg. Therefore, the economic output of rice under the two models is almost equal.

). At present, China’s rice–fish–duck system covers an area of about 8000 hectares, mainly distributed in the Guizhou, Yunnan, and Hunan provinces [48].

6. Broad Social Benefits

The rice–fish–duck symbiosis system has played an important role in the inheritance of Dong’s culture, biodiversity protection, and rural revitalization. The establishment of the rice–fish–duck farming system not only makes the ingredients such as rice, fish, and duck not polluted, but also plays a key role in maintaining the pure taste and nutritional content of traditional Dong’s food because the food chain is similar to the natural environment [30] (Figure 3A). These foods have also become a part of the Dong’s festival culture, making the Dong’s festivals more distinctive and, at the same time, giving birth to folk activities. For example, at the annual “ChunShe” festival in Long’e town, Liping county, the folk activity of “LaoShe” has become a carnival for the locals (Figure 3B). The “LaoShe” activity is that many men and women dressed in Dong’s costumes go down to large paddy fields to catch fish. Women wear Dong’s costumes, while men are topless. People use bamboo utensils to catch fish while chasing and playing in the paddy fields. Whoever catches the biggest fish is the champion, which means that he or she will have good luck in this year [31]. It can be said that the rice–fish–duck system embodies the Dong’s ecological wisdom of pursuit of purity, respect for nature, and sustainable development, and is a concentrated expression of the Dong’s culture.

The rice varieties as well as the fish and duck varieties in the Dong’s rice–fish–duck system have obvious local characteristics and are the wisdom crystallization cultivated by the Dong’s ancestors for thousands of years, in accordance with the local environmental characteristics. The Dong’s rice–fish–duck system has continued to this day, preserving a large number of precious glutinous rice varieties [32] and at the same time producing fish and duck species unique to the Dong nationality [33]. These variety resources have greatly enriched biodiversity and are valuable assets for the breeding of fine varieties.

The role of the rice–fish–duck system in developing the rural economy and providing employment opportunities cannot be underestimated. From 2011 to 2017, Congjiang county vigorously promoted the rice–fish–duck symbiosis model and developed the local tourism economy through it, achieving a total output value of CNY 4.46 billion and meeting the employment needs of a large number of rural women [34]. Yuanyang county has also developed local industries by vigorously promoting the symbiosis model of rice–fish–duck and has given priority to providing employment opportunities for local poor laborers, greatly promoting the local poverty alleviation and prosperity [35].

7. Technological Core and Innovation

7.1. The Technological Core of the Dong’s Rice–Fish–Duck System

Rice, fish, and ducks are originally three species that are mutually exclusive. Fish and ducks eat rice, and ducks eat fish. However, in the Dong’s area of China, they form a complex system of harmonious symbiosis between rice, fish, and duck.

A mystery is hidden in the species [49]. First, the rice cultivars in this system are locally cultivated glutinous rice (Figure 4A), which are characterized by high stalks and flood resistance. The high stalk allows ducks to walk through the rice plants and forage freely without hurting the rice spikes. The advantage of being resistant to flooding is that it can reserve deep water in the field to increase animals’ living space and expand the distribution area of bait, which is conducive to improving the output of fish and ducks, and can also avoid mutual restraint between fish and ducks. More importantly, the Dong’s rice–fish–duck system is located in the high-altitude mountainous jungle area where the light and heat resources are unfavorable and the local excellent glutinous rice varieties can just adapt to this environment. Secondly, the fish stocked in the rice fields are specially domesticated carp (Figure 4B). Carp feed on phytoplankton and will not attack rice roots and seedlings, nor will they attack other wild animals and plants that are of economic value to humans so they will not affect the overall output level of the paddy field. Finally, a special duck species with small size, fast breeding, long spawning period, and mixed eating habits—Xiaoxiang duck—is selected (Figure 4C). Only small individuals can smoothly walk between the gaps of high-stalk glutinous rice, foraging for various animal and plant baits, without hurting rice plants and roots, but can kill pests and weeds. In addition, the characteristics of fast breeding, long spawning period, and mixed feeding habits are beneficial to improve the economic value of ducks.

Another mystery is hidden in time [2]. In the first month of the lunar calendar, before the rice fields are cultivated, 3 days after hatching the ducks are put into the rice fields until the rice is sown. In the middle of March in the lunar calendar, about half a month after the rice is sown, the newly hatched fish are put into the rice fields. In the middle of April of the lunar calendar, the seedlings are transplanted. The fish will not disturb the fixed roots of rice because they are very small at this time so they can coexist with rice. Ducks are different and even juvenile ducks will disturb the fixed roots of rice seedlings. After the rice seedlings turn green, the body length of fish exceeds 5 cm and the juvenile ducks can no longer eat them; therefore, the juvenile ducks begin to be stocked in the rice fields. When the rice tillering is finished and the fish body length exceeds 8 cm, the adult ducks can also start to stock. Before the rice harvest, fish and ducks are caught. When the harvest is finished, the rice fields are opened to ducks again.

7.2. Modern Innovation of Rice–Fish–Duck Farming System

The Dong’s rice–fish–duck symbiosis system continues to this day, giving many valuable inspirations to the development of modern agriculture. At present, the compound breeding of rice–fish–duck is developing vigorously in various parts of China, and it has also been endowed with new connotations. First, on the basis of ensuring the harmonious coexistence of rice, fish, and ducks, varieties with higher economic potential were applied to the system, such as hybrid rice, grass carp, mandarin fish, and Muscovy duck [47,50]. Secondly, the species diversity of the rice–fish–duck system has been further improved, forming a variety of complex breeding models such as “rice-fish-duck-vegetable” symbiosis system and “rice-turtle-fish-duck” symbiosis system [51,52,53,54]. Finally, in order to achieve simplification in agriculture, regenerative rice [55] and perennial rice [56] were also applied to the rice–fish–duck symbiosis system.

8. Threats and Challenges Facing the Dong’s Rice–Fish–Duck System

8.1. The Transfer of Rural Labor to Urban Areas

The labor input of the rice–fish–duck system is huge, and there is no mechanized operation in the whole process. From sowing to harvesting, labor is inseparable. Moreover, under the modern pattern of economic diversification, the income of the farming system is relatively meager [36]. In this case, a large number of the rural labor force in Congjiang county flows to the assembly line factories in the developed eastern regions, resulting in a shortage of actual labor in rural areas. Due to the lack of labor, the paddy fields for rice–fish–duck farming tend to return to extensive use or be abandoned [37]. The rice–fish–duck system in Liping county is also facing the same situation. More than 90% of the young and middle-aged people go out to work, the agricultural labor force is seriously lacking and aging, and the terraced fields are seriously abandoned [38].

8.2. The Collision of Modern Agricultural Technology

The popularization of high-yielding hybrid rice varieties and the use of chemical fertilizers and pesticides have impacted the traditional rice–fish–duck symbiosis system [37]. Hybrid rice is less resistant to pests and diseases than Dong’s native glutinous rice and requires higher amounts of fertilizer [39,40]. Therefore, chemical fertilizers and pesticides are inevitably put into the rice field system, which adversely affects the survival of fish and ducks [41]. The harmonious symbiosis of rice, fish, and ducks was broken, and it also caused serious pollution to the local ecological environment.

8.3. Marketization and Industrialization Are Not Yet Perfect

In the rice–fish–duck breeding areas, there are widespread problems of weak degrees in product marketization and deep processing, and the tendency of the small-scale peasant economy is still very strong. Due to the low degree of marketization and industrialization, local farmers have been marginalized in the market economy for a long time, and their high-quality organic products have not achieved the high value they should have [37].

8.4. Diminution of Cultural Awareness

The production process and products of the rice–fish–duck system embody the traditional culture of the Dong’s people, which are reflected in festival celebrations, hospitality, and sacrifices. However, under the continuous impact of modern culture, inheritors of many long-standing traditional customs, religious beliefs, and etiquettes have gradually reduced, and many young people lack the understanding of traditional culture [40]. The old people with knowledge of breeding and farming have passed away one after another, and the inheritance of traditional culture is facing a threat [36].

8.5. Adverse Effects of Climate Change

Due to high population density, strong land dependence, remoteness, and backwardness, agricultural cultural heritage sites generally have high ecological vulnerability [42]. In recent years, the continuous reduction in precipitation in “DongXiang” has led to a corresponding reduction in the area of rice fields that can be transplanted [43]. Climate change will also force the areas of rice–fish–duck farming to decrease.

9. The Protection and Development for the Dong’s Rice–Fish–Duck System

The protection and development of the Dong’s rice–fish–duck system should adhere to the multi-center governance principle that guides governments and multi-party participates [57]. Implement protection and inheritance during development, and develop on the basis of protection and inheritance [37].

9.1. Delineate Active Protected Areas

The most ideal way to protect intangible cultural heritage is to protect and inherit it in its living environment, and the traditional Dong’s rice–fish–duck symbiosis system just constitutes the ecological environment and heritage field of the intangible cultural heritage [58]. Therefore, the government should improve the protection and compensation mechanism, implement active protection for the core area of the heritage, and maintain the most original way of livelihood for the Dong’s people.

9.2. Establish Scientific Research and Popular Science Bases

The rice–fish–duck system is the crystallization of wisdom of the Dong’s ancestors for thousands of years, and it also contains many unsolved scientific secrets. The interaction mechanism between biological populations, the genetic value of species resources, the ecosystem service functions, the ability to mitigate and adapt to climate change, and the stability maintenance mechanism of social and cultural systems have important implications for the development of modern agriculture. Therefore, the local government can cooperate with relevant universities and research institutes to establish scientific research and popular science bases, conduct in-depth scientific research, compile local agricultural knowledge teaching materials, set up local courses [54], and carry out agricultural cultural heritage knowledge learning and experience projects [59].

9.3. Improve Related Systems

The government should gradually improve the land transfer system and introduce relevant preferential policies to guide farmers to adopt the rice–fish–duck complex system, encourage young people to return to their hometowns to start businesses and achieve high incomes through large-scale production [60,61]. In addition, related legal protection systems should be established so as to clarify the ownership of heritage, stipulate the rights and obligations of each subject, reasonably determine the benefit distribution mechanism, and improve relevant supporting legal measures [62].

9.4. Develop Rural Tourism Market

As an agricultural cultural heritage, it can be presented to more people by integrating it into tourism. In the context of China’s rural revitalization, rural tourism and experiential tourism have become new choices for people’s travel. Therefore, different activities can be added to the rice–fish–duck agricultural model in different seasons to attract tourists’ interest in an immersive and experiential way [63]. At the same time, the local ecological products can be deeply processed to create characteristic brands and realize the integrated development of primary, secondary, and tertiary industries.

9.5. Innovate Farming Technology

The rice–fish–duck system is the traditional livelihood for the Dong’s people, and it is also an efficient modern agricultural production mode. Agricultural researchers should fully understand the comprehensive potential of this system, and make appropriate “combination” and “grafting” of the system according to local conditions, extending it to more regions to achieve innovative development. For example, collecting rice varieties with high economic value suitable for the rice–fish–duck system, increasing the variety of breeding animals, exploring light and simplified production techniques for the rice–fish–duck system, and developing multi-cropping.

10. Discussion and Conclusions

The rice–fish–duck symbiosis system in China is one of the globally important ingenious agricultural heritage systems, which has obvious ecological benefits, rich economic benefits, and extensive social benefits. Today, with serious environmental pollution, low agricultural economic benefits, and backward rural development, it has extremely important guiding significance for the sustainable development of agriculture. However, this system also needs innovation. First of all, rice cultivars with high yield potential, good quality, multi-resistance, waterlogging tolerance, and strong adaptability should be screened [50]. Secondly, rice-planting methods also need to be improved. Wide–narrow row can be used for planting, which can reduce the damage of ducks and fish to rice. Thirdly, select fish and duck varieties with high economic benefits that are suitable for rice field breeding [47]. Finally, the management of the rice–fish–duck symbiosis system also needs to be simplified. For example, adopt no tillage, promote small agricultural machinery, and encourage large-scale operation [60].

It is worrisome that the transfer of rural labor force, the promotion of modern agricultural science and technology, the low degree of marketization and industrialization [37,38], the fading of cultural awareness [40], and the change in climate [43] have posed a huge threat and challenge to the traditional rice–fish–duck system in China, and the protection and development of the rice–fish–duck symbiosis system is urgently needed. At the same time, rice–fish systems in the Zhejiang province of China, one of the globally important ingenious agricultural heritage systems, also faces the same situation. Economic development and industrialization pose a threat to rice–fish farming and, consequently, the numbers of farmers involved in rice–fish farming are decreasing [44]. Therefore, we suggest to delimit a living protection area, establish a scientific research base, improve relevant systems, develop the rural tourism market, and innovate farming technology [58,59,60,61,62,63], which have reference significance for the protection and development of other agricultural heritage systems.