A Review of Rice-Fish Culture in China

Freshwater Fisheries Research Centre
Chinese Academy of Fisheries Science
Wuxi, China

Network of Aquaculture Centres in Asia
Bangkok, Thailand
September 1986

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A Review of Rice-Fish Culture in China

Li Kang min

Freshwater Fisheries Research Centre, Chinese Academy of Fisheries Sciences, Wuxi China

Introduction

In China, fish culture in rice field has a long history which can be dated as far back as the mid Han Dynasty about 100 AD. [1]

Rice-fish culture is common in the southeastern provinces and also in the mountainous areas of the southwestern provinces where there are a few rivers or lakes but fresh fish are not available. Also because of the better economic returns rice-fish culture has gradually spreaded from the mountainous districts to the plain areas. However, at times the development of rice-fish culture has suffered in China because of changing techniques of rice palnting along with the wider application of insecticide and chemical fertilizers. In 1950s, it developed rapidly in Guangdong but in the early 1960s the area of rice-fish culture quickly shrank because of spraying of chemical insecticides. It did not recover until the middle of 1960s.

1. Economic Significance and the Rational of Fish Culture in Paddy Field

1.1 Economic significance

1. Paddy fields offer additional water area for fry, fingerling and fish production. Experiments show that the yield of fish could reach 15–150 kg per mu in rice fields through fish culture. There are 33 million hectared of paddy fields in China of which about 25.3 million hectares can be used for rice-fish culture. In fact, of the total area of 100 million hectares of paddy fields in the world, over 90 per cent is in south east Asia. With a modest production rate of about 75 kg in these fields rice-fish culture will produce 6.7 million ton of fish.

2. The fish culture in paddy field may markedly increase rice production. It has been shown gthat rice grows better in fields with fish culture and the yield is increased. The rate of increase is approximately 4–15%. In such fields where fish culture is undertaken, the paddy grow better, branch higher, panicle longer, effective tillering rate high, grains per tiller more, and the rate of empty grains low.

In reality, aquatic or terrestrial weeds also grow in rice fields along with phytoplankton and photosynthetic bacteria. They absorb the nutriments in the field. While these biomass are of no use to mankind, they are competitors for the nutriments with paddy. However, all of them are excellent food organism of fish. If fish are cultured in the fields, almost all the biomass could be utilized by fish resulting in effective utilization of the nutrients in the fields.

The weeds in rice fields consists of about 100 species such as duckweeds (Lemna minor). alligator weed Alternanthera philoxeroides, coontail Ceratophyllum, Rotala indica, Myriophyllum spicatum, Utricularia aurea, Potamogeton crispus, Potamo geton franchetii, Potamogeton malainus, Najas minor, Sagittaria pyqmaea, Hydrilla verticillata, barnyard grass Panicum crus-galli, Cyperus difformis, Heleocharis yokoscensis, Sparganium racemosum, Monochoria vaginalis, etc.

Many floating plants such as Azolla impricata, Spirodela polyrhiza duckweeds, Salvinia natans, can be directly swallowed by fish. Younger submerged plants like Utricularia, Najas, coontail, etc. are good food of fish. Fish eat the seeds of certain emergent plants such as Monochoria korsakowii, Scirpus yagara, Fimbristylis and thus control their propagation.

Besides mosquito and fly larvae and snails fish consume various harmful insects commonly occurring in rice fields. Yellow riceborer Tryporyza incertulas, Chilo simplex, brown plant hopper Nilaparrata lugens, Liburnia spp. etc. are fish food organisms which common carp crucian carp and tilapia quickly eat (See Table 1). Thus, fish loosen the soil to make it more aerable, it enhancing decomposition of organic matter and promoting the release of nutrients in the soil

The excreta of fish directly fertilise the water in rice fields. It has b-en seen that the concentration of nitrogen, phosphorus and potassium in rice fields with fish culture is higher than those without fish culture.

In fact, the recent development of fish culture in paddy fields in China is based upon the principles of biological control of weed through grass carp. Biological control of weed saves the manual labour for deweeding. Fujian Provincial Agricultural Science Academy conducted an experiment on rice-duckweed-fish culture and regarded this integrated fish farming as “Stereoscopic agriculture”.

“Rice-duckweed-fish” was carried out in 30 ha in the mountain districts and plains where yields of all the three products have been quite promising. Under the system the soil of the paddy fields is loosen by the fishes whereas fish faeces fertilize the field. Woffia and other weed and insects are eaten by the fish. Not only there is no need to weed or plough the field but chances of disease to rice are also reduced. The field without fish needs to be sprayed four times during the growth period however, in the experimental field spraying once was enough, The result showed the average fish production per mu is at the late of 57 kg. whereas for two crops of rice to 650 kg.

2. Preparation for Rice-Fish Culture

Paddy fields used for fish culture have different water characteristics compared to ponds and lakes. The water depth is usually shallow in rice fields. Because of the shallowness. the water temperature is greatly influenced by the air temperatures. Large quantities of oxygen are released during photosynthesis by the vegetation in the field. The dissolved oxygen content of the water is therefore high. Compared to ponds, more benthic animals and far more filamentous algae and aquatic plants are present the fields.

Usually, rice fields with adequate water supply, good drainage facilities, high water retention ability and abundant sunlight are suitable for fish culture. In the southern part of China, there are deep water rice fields in low lying areas near the lakes and along the rivers. These paddy fields are excellent bases for combined rice-fish cultivation.

2.1 Construction of water structure and sheds

In order to maintain adequate water depth and also to prevent escape of fish during heavy rain, the bunds need to be reinforced or if required raised also to 33.3 to 50 cm. A fish sump need to be provided as hiding place for fish during the season of shallow irrigation and high temperature, or when the field is drained dry or during the application of chemical fertilisers or insecticides. Harvesting of fish is facilitated if the fish are concentrated in trenches and sumps. Usually, fish trenches are built after transplanting the seedlings. (see plate 1) Facilities for filling and for draining, outlets with screens need to be provided on bunds at opposite corners of the rice field. Screening is done normally with a bamboo fence however, the water pipes are screened with wire netting.

At times it is advisable to construct a shed on top of the fish sump to protect the fish when water lemerature in rice field goes up to 39°C. In certain districts (such as in the rice field terraces of Sichuan), there is no fish sump, and a hole of 50–66 cm deep is made on the shaded side of the bund. This serves as a shed in summer and as an overwintering place in winter. These holes are particularly suited to the catfishes which prefer dim light.

2.2 Fish species

The species most commonly used are carps and tilapia: common carp, crucian carp, bighead, European crucian carp, mirror carp, catfish Clarias, loach, rain bow trout, Xenocyprinus and snakehead Ophicephalus argus, etc. However, Macrobrachium species and viviparus may also be suitable for culture in rice fields.

2.3 Stocking size

The fry and fingerlings stocked in rice fields should be healthy, stout with the surface of their bodies intact, and their scales undamaged. The optimum size of stocking of common carp is 6.6 cm – 8.3 cm (preferably 10 cm or above); silver carp and bighead, 10–13.3 cm (preferably 20 cm or above). Catfish, crucian carp, mud carp, etc. yearling and tilapia, fingerling after overwintering, are stocked.

2.4 Stocking rate

Stocking rates differ in different areas because of different in the species and in the size of the fry cultured, in rice farming techniques and also different type and quantities of fertilisers used.

Paddy fields are also used for breeding of fish and raising of fry and fingerlings. Hatching of common carp eggs in rice field is undertaken when it is filled with water to 10–13 cm. Fish nests with common carp eggs attached are released in the field at a rate of 3–4 bundles per mu (about 30–40 thousand stickly eggs).

In general fry is stocked at the rate of 50–100 thousand per mu for the purpose of raising them to summer fingerlings. However, at the Wuxi Aquaculture Station, with no supplementary feeding and the water level of 8–10 cm, the stocking rate is 1,500 fry per mu. At the time of the rice harvest, they grow to approximately 10 cm size. In Guangsi during the cultivating period of early rice 2.7–3.3 cm common carp are stocked at a rate of 400–500 per mu in late April and they grow to 13.2 cm and weight approximately 35 gms in July without supplementary feeding. Survival rate is 20–50%.

Stocking rate of 1,000 – 1,500 fry of common carp per mu appears to be suitable where no supplementary food is given. However, this rate can be proportionately adjusted based on the fertility of the rice field. Rice fields in the mountain areas of Guangsi usually have slightly acid soil, and the production of natural food organisms is less than that with alkaline soil. Here a stocking rate of 400–800 per mu is considered suitable.

2.5 Stocking rate of Juvenile

In certain area of Guangsi where juveniles are reared to adults with two harvests of rice each year, 130–180 common carp of 10–15 cm are stocked with no supplementary feeding. The yield normally varies from 10–12.5 kg per mu in three months (Aug. - Oct). In Guangong, where tilapia is the dominant species to be stocked in rice fields in summer they are stocked at the rate of 200 fry of 2.3–2.6 cm along with 20 grass carp, 10 bighead, 9 silver carp, 33 common carp; 12 crucian carp Carassius auratus gibelio. In winter, crucian carp C. gibelio is stocked as the dominant species with stocking rate of 100 per mu in combination with 15 grass carp, 7 bighead, 8 silver carp, 22 common carp. Thus the average stocking rate per mu is about 150 individuals. The yields in two seasons can reach to about 150 kg or above.

When grass carp summer fry are reared to fingerlings they are stocked at the rate of 1332 fry of 3.5–6.0 cm per mu in association with 100–200 silver carp or bighead which grow to approximately 20–26.6 cm.

3. Integration between Rice Farming and Fish culture

Rice-fish culture can be classified into two methods; rice-fish culture in rotation and rice-fish culture in mixed farming.

3.1 Rice-fish culture in rotation

In some areas, the rice fields are left fallow in winter. Fish culture is undertaken to utilize these fields after the harvest of late rice or just before the cultivation of the early rice next spring. Since these fields are usually submerged all the year round they are very rich in planktonic and benthic organisms. After harvesting the rice, the field is tilled but not levelled and the fish are stocked In some areas, small quantities of lime are applied in the field after the harvest. This not only serves to disinfect the field, but also hastens the decay of the remains of the rice plant. The bunds are reinforced and if necessary the height is increased so that the field can hold 33.3–66.6 cm depth of water. Winter vegetables or beans are usually grown at the inner side of the bund. The major species used for stocking are the common carp and crucian carp, however, some silver carp and bighead are also stocked. The stocking rate varies according to different areas. Supplementary feeding to fishes and fertilization of field are normally done. Besides keeping the water at a level of around 66.6 cm, cross-shaped fish trenches and large fish sumps measuring a few aquare meters are also constructed. The fish sumps are provided at the top with sheltering sheds which are further covered by branches and straw to keep them warm. Pig and cow manures are stacked beneath the sheds to serve as fish feed. In Guangsi areas, these sort of structure are called “fish nests”, which may be sirrounded with small bamboo, willow, etc. to protect the fish from predators throughout winter.

3.1.1 Fish culture in winter fallows

Winter fallow fields are mainly used for rearing spring fry for stocking them in ponds and lakes next spring. In some cases, adult fish are reared and the culture period is extended from the rice crop to winter fallows.

In Sichuan paddy fields with higher bunds and with adequate water are selected to rear fry to fingerlings. The fields are deweeded and about 150–200 kg of quick lime is applied to kill predators and pathogen, and then smooth field is sundried for few days. Nightsoil 200–250kg is applied 2–3 days later. The field is filled with water to 33 cm depth when 10–20 thousand fry are stocked. Five days later, manures are applied at a rate of 5 kg per day. If the water is too fertile, some fresh water is added to the field. When fi gerlings grow to about 6.6 cm, they are harvested and can be further stocked for longer period where already paddy plantation is growing.

In Shanxi, an experiment was undertaken to stock rainbow trout in winter fallows of an area of about 0.15 ha with flow of water of 5–8 tons hours. 1200 fingerlings with an average weight of 40g/ ea were stocked. The water temperature was 7°C-13°C. Fingerlings were fed 3 times a day from mid December to late April. The production of fish was 203 kg with an average weight of 0.15-0.5 kg/each.

3.1.2 Fish culture in summer fallows:

After the harvest of early rice, the rice field is filled with water and stocked with fingerlings and the harvesting of fishes takes place before transplanting of late rice. Therefore, the rearing period is rather short (40–60 days) with little or no supplementary feeding.

The following measures are taken to undertake fish culture in summer fallows:

1. The bunds are raised to keep the water at a depth of 50 cm - 88.3 cm and fish sumps are provided.

2. Suitable fish species with high temperature tolerance are stocked. Common carp and tilapia are commonly used because of their adaptability to higher water temperature in the range of 20–30°C.

3. Selection of the early rice variety; broadcasting and transplanting them in advance; and harvesting in time are essential to extend the rearing period of fish.

4. Although the high temperature is conducive for the growth of fish, but chances of fish diseases also increase in such temperature. Therefore, proper attention is required to control the disease.

3.1.3 Fish culture in both Summer fallows and Winter fallows

In Hunan, the method of “Two crops of seedlings and two harvests of fingerlings” is practised. When the early maturing rice are transplanted, fry are stocked to be reared to fingerlings for 40–50 days, and then the field is used as late rice nursery. After transplanting of late rice, the field is again used to rear fingerlings. The fry and fingerlings grow well because of the high fertility of rice nursery.

In Guangdong, fish culture in summer fallows is the same as above and after the harvest of late rice, the rice field is filled with water and stocked with fish. The fish are reared in winter fallows. The rearing period is about 100 days. In spite of the longer time of fish culture in winter fallows, the fish production in summer fallows is greater than the winter fallows mainly because fish grow better in higher water temperature in summer.

3.2 Rice-fish culture in mixed farming

The method employed in culturing fish in doble crop rice field varies according to different methods of paddy cultivation in different areas. In Jiangsi, fish culture is commonly practised with intercropping of rice. In Hunan and Zhejiang, fish are cultured in rice fields with consecutive rice crops, and in other areas of Jiangsi, fish are only cultured during the farming seasons of the second crop of late maturing rice.

3.2.1 Fish culture with intercropping of rice:

Usually transplantation of rice is undertaken in early spring. The seedlings are allowed to grow for over a month. Seedlings of the second crop of late rice are transplanted between alternate rows of early rice. Stocking is usually done immediately before or after this transplanting period.

In one area of Jiangsi, however, the fields are stocked after harvesting the early maturing rice, and the stocking rate is at an average of 1,000 grass carp per mu for 3.3–6.6 cm. fry, which are mixed with 200 3.3cm fry of silver carp and 300 common carp and bighead. Fish trenches and sumps are constructed a few days before stocking. The trenches are made 16.6–20 cm deep, around the field or in the shape of a cross. Paddy dug out during the construction of fish trenches are replanted at the inner wall of the bund, and the production of rice per unit area is thus unaffected.

3.2.2 Fish culture with two crops of consecutive rice:

Fish culture with consecutive crops of rice is mainly undertaken for raising fry during early paddy and for raising winter fry or food fish during the second paddy.

Fish culture in the late paddy requires a greater depth of water because of the hot weather and the higherwater temperature. This is similar to rice cultivation in summer when more water is required.

Fish culture with consecutive late paddy usually starts at the end of June and the fish are harvested in early October before the rice harvest, giving a total rearing period of three months.

3.2.3 Fish culture with intercropping of rice and wild rice stem Zizania latifolia, (a kind of vegetables)

Wild rice stem is commonly cultivated in the southern provinces, as intercropping with early paddy together with fish culture. Zizania is grown in Hunan to prevent fertile loams to become water logged. Combination of fish, rice and Z. latifolia is ecologically compatible and economically more profitable. In the initial stages after wild rice stem are plated, growth of rice is not affected because wild rice stem are small. The period of rapid growth for Z. latifolia follows the harvesting of the early paddy. At the same time aeration and the amount of sunlight are increased because of the harvesting of the paddy, which are highly condusive to the growth and development of Z. latifolia. The fields for Z. latifolia have a water depth of 16.6–20 cm, which is very favourable to fish culture. Thus, paddy fields which are relatively more fertile after several years of fish culture are best used for growing Z. latifolia together with fish.

4. Management of Rice-Fish Culture

In rice-fish culture, knowledge of paddy farming and of the fish farming are essential. In addition, methods of filling, draining and the application of fertilisers and insecticides must be properly understood.

4.1 Routine Rice field management:

1. Watch on water structure is essential to keep adequate amount of water and control the fish escape.

2. The optimum water depth of 16.6 cm need to be maintained. However, when the field is drained, it should be done smoothly so that the fish could reach fish trenches or sumps.

3. Attention should be paid to the fluctuation of water temperature which may go up to 38–40°C beyond the tolerance limit of common carp (Juvenile common carp 38–30°C; yearlings, 26–27°C). In such cases the water ought to be changed with freshwater or fish sumps adequately shaded.

4.2 Relationship of fertilization and rice-fish culture

It has been seen that the growth and development of the paddy and the fish are greatly influenced by the kind, quantity and the method of application of the fertilisers. Nitrogen, phosphorus and potassium fertilisers needed by the paddy are also nutrient materials required by the natural fish foods such as the planktonic and benthic organisms. Thus, the availability of fertilisers in a rice field directly influences the production of fish food.

The Aquatic Biological Research Station of the Chinese Science Academy and the Aquaculture Research Station of Zhejiang have studied and determined the safety dosage of the commonly used chemical fertilisers to fish. Results suggest that at a water depth of 6.6 cm, the safety dosage for fry of common carp per mu (one application) is 10–15 kg of ammonium sulphate, 5 kg of ammonium nitrate, 2.5–7.5 kg of potassium nitrate, 5–10 kg of super-phosphate, the latter can be increased to 30 kg per mu without harmful effects to fish. The safety dosage for lime at a water depth of 6.6 cm is not exceeding 10 kg per mu.

Ammonium carbonate and urea have been found to be most suitable. The amount of ammonium carbonate is 15 kg, and irea 10 kg. Normally ammonium chloride or ammonium sulphate are not used in fish-rice culture since fish is effected by them. If ammonium bicarbonate is used as supplementary fertiliser, it must be buried deep, 6.6 cm beneath the surface of the soil. The amount of application should be below 15 kg. Fertilisers may be used in granular form for the safety of fish. Before application of chemical fertilisers, the water in the rice field may be drained to a certain level to let fish concentrate in fish trenches and sumps, and also to react the fertilisers immediately with the soil and be absorbed by the roots of the paddy and then the depth of water can be resumed to normal level. In this manner harmful effect of fertilizers to fish is greatly reduced.

In areas of Zhejiang, southern Jiangsi and Guangdong excretory material from silk worm is used as supplementary fertiliser; which has 1.45% of nitrogen, 0.25% phosphorus (P₂O₅), 0.11% potassium (K₂O). Silk worm faeces contain urea, which is harmful to fish if applied fresh. Therefore, silk worm faeces are applied after fermentation.

4.3 Relationship of the Application of Agricultural Chemical (Insecticides and herbicides) and Fish Culture

There are over 50 species of insects which are pests to rice and over 10 diseases have been recorded. Among these, the most common and damaging ones are the yellow rice borer Tryporyza incertulas, Chila simplex, green rice leaf hopper Nephotettix apicalis, rice plant skipper Parana guttatus, and rice blast, followed by Lagynotomis assimulans, rice leaf roller Cnapholocrocis medinalis, Lama flavipes, Oxya velox, and brown spot Cochliobolus miyabeanus. The species causing the most damage in Asia is the yellow stem-borer. In Malaya the most serious stem-borer is the dark headed striped-borer Chilo polychrysa while the most serious pest in Java is the white stem-borer Tryporyza innotata. Although fish, cultured in paddy fields, can eat part of pests and play the role of biological control but fish can not totally control them. Application of insecticide becomes essential. Lethal concentration of such insecticides to fish is shown in Table 2. It is important that before the application of such insecticide the field is drained and fish driven to the trenches and sumps. Volume of water is increased or water is kept changing. Chemicals if in powder form, should be applied in the early morning with dew while the sprays should be applied after dew dries. Derris, toxaphene and pentachlorophenol are prohibited in rice-fish culture.

4.4 The Prevention of Predators for Rice-Fish Culture

In the paddy field, fish predators are many: such as birds, animal, snakes, frogs, Cybister sp., Ranatra sp., and Lacotrphes japonensis, etc. The prevention of predation is most important in the early stages, when the paddy is small, and the field is quite exposed. Coupled with this their swimming makes them very susceptible to predation. Again at the harvesting period when the water is shallow they are exposed to predators Thus, it is necessary to prevent loss by controlling these predators through better management. Also, increasing the water level may be effective in minimising predation provided the growth of rice is not adversely affected.

4.5 The Relationship of Shallow Irrigation and Sun Drying with Rice-Fish Culture

The paddy are subjected to shallow irrigation at certain periods to increase production. To satisfy the oxygen requirements of the root system, the amount and time of irrigation need to be adjusted during the growing period. To promote tillering (and not development) it is necessary to have shallow irrigation whereas in the growth period, a lot of water is needed and the water level in the field need to be increased. There is also an urgent requirement for more water before and after the development of panicles and the field need to be filled. However, during shallow irrigation, the fish are still small and their activities are not affected by the shallowness of the water. As the rice and the fish grow together the water level is also increased and this practice basically satisfies the requirements for rice-fish culture. Thus, there is no conflict between shallow irrigation and fish-rice culture.

According to experience gained by Zhejiang farmers, sun-drying of rice fields has no adverse influence on fish. For example, in 1959, 5.52 mu of paddy was experimented with fish culture and two crops of consecutive paddy. Cross-shaped fish trenches (40 cm wide, 26.4 cm deep) and 3 sumps (2.33 m length, 2 m wide and 1.16 m deep) were constructed. Transplanting was carried out in April 16 at intervals of 6.6 cm × 16.6 cm. The water depth was about 3.3 cm and fish was stocked 8 days after transplanting. An average of 362 common carp of 6.6–16.6 cm, 1811 crucian carp of 2.3 cm were stocked per mu. At the same time, the field was drained for tillering. After tilling, the field was again filled and further stocked with 2.3 cm crucian carp at a rate of 2,000 per mu. The field was again tilled 5 days and another 7 days after. At each tilling, the field was drained and the fish concentrated in fish trenches and fish sumps. After 3 tillings, the field underwent sun-drying for about 10 days until small cracks in the soil were evident. During sun-drying, the fish were concentrated in the trenches and sumps. To provide food for the fish during this stage, 5 kg of cow dung was supplied to the trenches and sumps at alternate days. The early paddy was harvested on July 12 with an average yield of 491 kg per mu. Late paddy was transplanted on July 13 at intervals of 10 × 20 cm. The field was drained and tilled twice on July 18 and August 7 respectively. The field was then sun-dried for 12 days, during which 21 kg of ammonium sulfate and 2.74 kg of 666 powder were introduced on August 10. As the fish was concentrated in the trenches and sumps, no adverse effect was detected.

5. References

1. Chinese Fresh Water Fish Culture Editorial Board: Science of the Culture of Freshwater Fish Species in China. IDRC-TS16E P415. 1982.

2. Ca Ren-kui: Rice Field Fish Culture, Agricultural Publisher, May 1983.

3. Nie Dashu, Chen Ying hong, Wang Juanguo: Recent Development of Fish Culture in the Rice Paddy in China" abstract, Oct 1985

4. Fujian Provincial Agricultural Science Academy: Rice-Duckweed-Fish integration, July 1984.

5. J.W. Purseglove: Tropical Crops Monocotyledons, Longman ISBN 0 582 46606 7, 1972.

6. Unearthed cultural relics of East Han from the excavation in Main County, Shaanxi Province 1978.

Table 1 Comparison Study of Pests in Rice Fields With and Without Fish Culture

Table 2 The Half Lethal Concentration of Several Chemicals to Fish in Rice Fields

Note: (1) The concentration is measured according to the effective constituents.

(2) The normal concentration is at the depth of 5cm when all the drug drops into the water.

(3) The harm is just to common carp and crucian carp. The symbol “+” means not dead; “-”, dead; “±” possibly dead.