7. FISH CULTURE IN RICE FIELDS - CULTURE OPERATIONS

Culture operations of rizi-pisciculture or rice and fish in rotation vary from country to country, but we shall refer to a general norm first and then pick out the differences in practices as applicable. I shall describe the pond preparation for rizi-pisciculture as described by Coche (1967) and then the design of rizi-pisciculture plot, described by Coche (1960): The culture operation for rice and fish will be dealt with subsequently.

7.1. Preparation of Rice Field - General

When fish culture is planned the rice fields should be provided with strong and impervious bunds - the height of the dry bund should be at least 25 cm, but a height of 60 cm is recommended; the latter is often the height of bunds of paddy fields in several places in Asia. The slope of the bund should be about 30 – 45 degrees, according to Coche (1967), but large well built bunds can have slopes which are less. The bunds should help retain water and in new fields water retention of about 10 cm depth for several weeks should be confirmed.

It is useful to have trenches and sumps to be used as fish refuges in rizi-pisciculture plots. They can be dug on one side of the plot only, all round (peripherally, adjoining the bunds) or diagonally across in each plot (see Figs 3 and 4), their number, contour and size depending on the size of the plot, soil and fish stocked. Larger fields can have more trenches (see Grover, 1979). As we have explained elsewhere deeper trenches help as a protection against extremes of water temperatures. The width of the trench should take into consideration the size of the fish harvested - the width usually varies between 50 and 180 cm and the depth from 30 to 90 cm. Depending on the soil type the sides of the trenches are sloped at 30 – 45 degrees.

Sumps, or larger pits, are usually provided in the plot, for fish to take refuge in times of need and also to facilitate harvest. The sumps are provided usually near the water inlet connected to the trench and also near the outlet. In some cases the sumps are made at the junction of several trenches. The size of the sumps could be several square metres (see Figs 3 & 4) and their depth is often higher than that of the trenches. Water inlet and outlet enable supply and drain of water - their designs vary. In Asia bamboo pipes and screens are often used. A spillway (overflow) properly placed helps in reducing fish losses due to accidental overflooding of the bunds.

7.2 Description of a rizi-pisciculture plot

The following is a description of rizi-pisciculture plot (Fig. 3) described by Coche (1960), who used it for his experiments at Kipopo in Zaire.

The area of trenches and sumps cover in this case 12.1% of the total area; in Taiwan it is usually 5 – 7% - see also studies made by Grover (1979), idscussed later Trover did not find any increase in fish production with increase in trench area from 10 to 23% of rice field.

Dykes (bunds) - Height: 60 cm; width at base: 180 cm
width at top: 60 cm; slope - 45°

The bottom of the field is a plain, with the trench dug diagonally across, with two sumps at each end (see Fig 3). The trench has a width of 180 cm, a maximum depth of 60 cm and a slope at the bottom of 5/1000 permitting complete and quick draining.

Of the two sumps (additional refuges), the one at the inlet point has an area of 9 M² (3 × 3) and the other at the outlet, 24 M² (6 × 4). From the latter the outlet made of bricks pierces through the dyke. The water inlet and outlet (both have to be provided with grills and screens to avoid unauthorised fish entry and escape) allow control of intensity and level of water, a constant supply of water, transforming the field into a pond with 50 cm depth of water and also if needed to maintain the field entirely dry. This description is only of one type of rizi-pisciculture plot - variations to this is possible as discussed elsewhere.

7.3 Rice culture operations

As we have already discussed is grown usually in areas where there is good rainfall, but as obvious in lower rainfall areas where irrigation facilities are available rice can be grown. In organized cultivation, fields are partitioned into plots, bunded on all sides, with facilities for supply of water through dams, reservoirs, tanks and canals and also proper draining and control of water flow and levels. Usually the rice cultivation begins with the onset of rains (monsoons). The fields which remain dry are got ready and rice is grown either directly by sowing or by transplantation from nurseries.

Fig. 3. Other possible trench-refuge combinations in rice fish culture plots (not to scale) (see also Fig. 4.)

Fig. 4. An experimental plot of rizipisculture (After Coche, 1961)

Depending on the type of land and water availability one, two or even three rice crops are taken. In areas which are less fertile and often supplied with less water rice production will be less intensive, and a rice crop may be followed by other vegetable crops which need less water. Now improved technology of rice production, has ushered in (i) improved rice varieties (lesser duration, high yielding varieties), and (ii) better agronomical practices of (a) fertilization (b) plant protection and (c) water use. These have resulted in certain parts of the world, in green revolution, in doubling the production of rice from the same piece of land in Asia.

Improved varieties are being produced every year by the rice research centres of the world e.g. IRRI (International Rice Research Institute) in Philippines and various national Agricultural Institutes and Universities. Coche (1960) used the rice variety RZE 90 (INEAC - YANGAMBI) and gives complete detail of the cultivation. Several high yielding rice varieties such as IR 8, IR 20, (Cf IRRI), CO 25, ADT 32 etc. are used in South India for cultivation. Grover (1979) describes his rizi-pisciculture trials with the IRRI variety, IR 26 (see later) IR 26, 30, 39, 32, 36, 38 and 40 have been used for culture along with tilapias and carps (Arce and Dela Cruz, 1978) (see also Table III). Rice breeding has brought in now varieties of short duration (105 – 125 days) - older varieties often had longer duration crops - about 160 days. Coche (1960) used RZE 90, whose duration was 185 days. The length of duration of crop is important in view of the pisciculture practice to be adopted. Different growth stages and culture operations for a 120-day and a 150-day rice crop (along with fish stocking times), (Singh et al (1980) are indicated in Fig. 5

A short description of conditions and methods of rice cultivation as described by Vincke (1979) is given hereunder:

As already mentioned earlier, the rice is the principal crop and fish is only a secondary, but useful, crop in rizi-pisciculture. Thus the fish culture will be subject to, or controlled by, the conditions of rice culture. We shall however, attempt to produce optimum levels of production of rice and fish modifying the culture technology to the extent possible. As already referred to, rice culture can be done either by sowing the seeds directly in the field or by transplanting the seedlings grown in a separate nursery to the field. Vincke (1979) states that the rice crop duration usually varies between 120 and 140 days (see earlier).

The fish can be stocked in the rice fields 8 days after transplanting or one month after sowing seeds in direct cropping. Usually the fish and rice culture subsequently could last for 100 days. Depending on the place and conditions (see earlier) there will be a single or multiple crop of rice in a year and thus successive culture of fish in the same field also is possible. Generally there is only a single crop in one year, but in some countries (e.g. Indonesia India, China and Madagascar) two crops in a year are taken. After the rice crop/s during the fallow period usually the field is left to dry or is converted into a pasture; in some cases where water is available the field can be converted into a pond and fish and duck can be cultured, as done in Madagascar. In certain parts of India (kerala) even though ducks are not regularly cultured in the rice field after the rice crop, ducks raised elsewhere are often brought and left in the harvested paddy field for feeding (‘grazing’) temporarily). The drying of the field during off season is, however, of advantage in aerating the soil, inducing mineralization, (killing off vectors such as snails and mosquitoes) and in also getting ready the field for transplantation of paddy for the next crop in preparing the trenches, fertilization etc.

When a second crop is taken from the field the same lot of fish grown during the first rice crop (about 100 days) can be grown in the second crop of rice also - in this case the fish cultured should be temporarily stocked in between in a “stocking” pond (e.g. growing of breeder carp in Japan).

As mentioned earlier, if fish is to be cultured in the field when rice is grown directly after sowing the fish are to be stocked only a month after sowing. In the case of transplantation of rice, fish are to be stocked only after a week after transplantation, while sowing seeds in nursery. Coche (1960) used 8 kg of dry grain/are (Var: RZE. 90). Usually 30 day old rice seedlings (15 – 20 cm height) are transplanted (40 – 20 cm or 50 – 10 cm apart) from the nursery to the rice field proper. The field will be dry on transplantation and only little (less than 5 cm) water will be allowed in the field in the few days after transplanting. Fish like carp if let in then, would pull out the rice seedlings. (However, a small earthen bund, a few cm high, can be built temporarily on the sides of the trenches (canals) and sumps in the paddy field, so that the fish in the “refuges” will not invade the ‘rice’ area until the seedlings are sufficiently rooted and strong). Subsequently the level of water in the rice field is increased to 10 – 20 cm, which is still inadequate for certain species of fish, but the water in the trenches and sumps (40 – 60 cm) should be offering sufficient refuge for the fish in rizi-pisciculture.

Application of biocides (plant protection) and fertilizers should be done judiciously so as not to affect the fish, as we have already discussed. Weeds appearing in the rice field are better removed mechanically rather than by weedicides.

We have already referred to the regulation of water in the rice fields for fish culture, specially with specific reference to providing extra deep water for the fish in trenches and sumps serving as fish refuge and also to control of water flow and level with appropriate inlet and outlet.

7.4 Fish culture operations

The rice field is made ready by cleaning it of weeds and vegetation, preparing (repairing) the bunds, trenches, sumps, water inlet, outlet etc. the water inlet and outlet, the latter pierced through the bund, at the bottom so that water can be drained out fully, are provided with suitable screens and nets in grooves, so that trash (weed) fish would not enter the field and the fish stocked would not escape. After the transplantation of seedlings is over (with a little of water only on the bottom favouring rooting of the seedlings), water level is raised in the field to 10 – 20 cm, so that the fingerlings of fish can be stocked.

Fig. 5. Summary of growth stages for 120- and 150-day rice culture: A, stocking times for fish fry when direct seeding is used; B, stocking times for fish fingerlings when direct rice seeding is used or fish fry when transplantation is used; C, stocking times for fish fingerlings when transplantation is used (Redrawn from Singh et al, 1980)

Suitable species available are chosen (see “Principal species used in rizi-pisciculture”). The most common species are Cyprinus carpio, Tilapia mossambica, Trichogaster pectoralis, Ophiocephalus (Channa) striatus and Clarias batrachus. In Africa, T. macrochir, T. melanopleura (T. rendalli), T. nilotica and T. zillii have been tested successfully. These fish are used in Monoculture (see Table VII also) or polyculture.

7.4.1 Polyculture of fish:

Coche (1970) used successfully the polyculture of T. macrochir, T. melanopleura (T. rendalli) and Haplochromis mellandi in Zaire (see also “Biological control of weeds, snails and mosquitoes in rice fields” - separate handout given) In India polyculture of Catla catla, Cirrhnia mrigala and Labeo rohita with other fish such as Anabas testudineus and Ophiocephalus (Channa) striatus has been practised. In Indonesia a combination of Osteochilus hasselti, Puntius javanicus and at times Chanos chanos, has been cultured in the rice field. In Malaysia, Trichogaster pectoralis, Clarias batrachus and Ophiocephalus (Channa) striatus, have been cultured together. Polyculture (see: Pond culture) has the advantage in that the different feeding niches in the ecosystem (rice field) are being fully utilised resulting in enhanced fish production.

7.4.2 Stocking of fish in rice fields:

The number and size of fish stocked would depend on the type of culture (for production of fingerlings - nursery; or for production of table - size fish), on the species of fish under culture and the specific local conditions. Vincke (1979) reviews the literature on the stocking densities of fingerlings fish in rice fields (see Table VII attached). The stocking density of fingerlings varies from 2 to 1000 per ‘are’ (note 1 ha = 100 ares), but conditions of culture has been varied, for in some cases the fish were fed supplementarily. In Cote d'Ivoire and Taiwan stocking densities of Tilapia varied from 30 – 80 per 'are! The size of fingerlings stocked also varied considerably, from 1 to 12 cm, from available data. In Indonesia 1 cm (fry) common camp have been stocked at 600 – 1000/are apparently using the rice field as nursery, but the stocking rate of larger fingerlings (upto 12 cm) varied from 10 – 100 per are. Since the rice field has been known to be fertile and rich, it can be stocked well with fingerlings to grow to table size fish; when supplementary feed and additional fertilization are available more fish can be stocked, but perhaps lesser densities than those recommended for pond culture are to be adopted in view of the lesser and stricter regime of water.

7.4.3 Fertilization:

The fertilization of the rice field is often done at the preliminary stage itself, in many parts of Asia, by using cow dung and green manure. Inorganic fertilization is also resorted to. Coche (1960) used and organic manure (compost) dose of 1000 – 2000 kg/ha/year. He also used ammonium sulphate (50 – 100 kg/ha). Coche also cites application of the following inorganic fertilizer in Madagascar in paddy nurseries:

(or 10 – 15 kg of wood ash/ha).

Vincke (1979) states that in Madagascar usually nitrogen, as Ammonium sulphate is applied at 300 – 400 kg/ha, around the 45th day after transplanting seedlings. This application did not affect the fish in the refuges. In Liberia on the 80th day after transplanting 50 kg/ha (of urea) was applied - during the operation the field was kept dry for 1/2 day, (Vincke, 1979), but it is known that most fish species can tolerate some amount of urea concentration, provided dilution is high - perhaps the fertilizer application has to be done in parts to save sensitive fish. Organic manures can also be applied in small dosages. It is stated that when fish are grown with rice the fertilizer dose for rice should be doubled. Fertilizers applied lead to better growth of paddy and also plankton and other fish food organisms.

7.4.4 Supplementary feeding:

Since the rizi-pisciculture is an example of integration of agriculture and pisciculture, as many products as can be recycled from one crop to the other will be of value. Rice bran and rice and other agricultural products like maize, cassava, and others - e.g. the oil cakes (groundnut, cotton seed etc) can be included in the feed for fish. In Japan silk worm pupae are included in the fish diet formulated. Pelleted feeds also can be given. The amount of feed given can be as in the case of ‘Pond Culture’, i.e. 5 – 10% of body weight of fish. In Madagascar 10% of fish weight is given as feed in rizi-pisciculture. In other cases a feed of 2 – 8% body weight has been given (Vincke, 1979).

7.4.5 Application of Pesticides and Weedicides:

This has to be done judiciously, preferably before the transplantation itself. Subsequently if applied, either the fish should be removed or dosages should be light - see earlier discussion on use of organochlorine and organophosphorus insecticides on fish. Matura Kimura and Tama (1958) showed that for common carp, Dieldrin and Endrin are more toxic than Diazinon, Dipterex, DDVP and Folidol. At the International Rice Research Institute it was shown that common carp is less sensitive to Lindane than Tilapia (IRRI, 1964). In Madagascar it was also shown that Lindane at 0.5 kg/are, as applied, did not kill fish (1976). The relative toxicity differencies of carp and T. mossambica to various organo-phorphorus compounds and Endosul an was discussed earlier. At all times it appears that pesticide application in rizi-pisciculture plots is dangerous, for even if it does not kill, the biocides could accumulate in fish.

Table VII

Stocking density of fish (monoculture) in rice fields
(From Vincke, 1979)

a = without supplementary feed
b = with supplementary feed.

7.4.6 Fish and Rice harvest:

It is usually necessary to keep the field dry for a week or so before the harvest of paddy, so that the paddy seeds will mature well and dry. It is best to harvest the fish before this process. The water can be drained out and fishes made to collect in the sumps or refuges, and netted out. If the same fish are to be restocked they have to be removed to a nearby temporary tank or pond, and retained until restocking.

7.4.7 Restocking:

If the same lot of fish are to be restocked either for a second rice crop or in a fallow field, the field has to be cleared of weeds and vegetation, the bunds, trenches, sumps and inlet and outlet repaired, and water filled again. It would be necessary to add manure/fertilizer again. If rice is not repeated the water level can be increased to 40 – 60 cm or higher if possible and fertilization adopted as in a culture pond, so that sufficient plankton develops in the water. In such conditions fish doubled its weight in two months (Vincke, 1976).