by
S.W. LING
FAO UNDP/TA Regional Fish Culturist for Asia and the Far East
Bangkok, Thailand
Abstract
Practical methods are given for culturing and farming M. rosenbergii on a large scale. Suitable water conditions, food, tanks, ponds, buildings and equipment for all stages are specified. The scheme covers rearing to early juvenile stages under hatchery conditions and the subsequent stocking of ponds and padi-fields.
METHODES D'ELEVAGE DE
Macrobrachium rosenbergii (DE MAN.)
Résumé
La communication décrit des méthodes pratiques d'élevage de M. rosenbergii à grande échelle. Elle indique les caractéristiques auxquelles doivent satisfaire l'eau, l'alimentation, les réservoirs, étangs, constructions et matériels requis à tous les stades des opérations. Celles-ci vont de l'élevage en “pouponnières” jusqu'aux premiers stades juvéniles à l'immersion en étanges et rizières.
METHODOS DE CRIA Y CULTIVO DE
Macrobrachium rosenbergii (DE MAN)
Extracto
Explica el autor métodos prácticos para el cultivo y cría de M. rosenbergii en gran escala. Detalla las condiciones convenientes del agua, alimento, tanques, estanques, edificios y equipo para todas las fases. El plan comprende la cría en piscifactoría hasta las fases juveniles y su traslado posterior a los estanques y arrozales.
Young and mature prawns suitable for culturing and breeding purposes may be collected from rivers, lakes or other natural habitats, with trap, line and hand-net.
Traps made of bamboo splits or galvanized wire netting, baited with coconut, fish or prawn, are set near the bank in the afternoon, and the catch is removed early in the morning. Mesh size is determined by the size of specimens expected.
Brush traps (large bundles of branches), set near river banks, are often effective in attracting fairly large numbers of young prawns. In places where the water is less than 10 ft deep and the bottom is fairly free from logs and stones, a cast-net can be used.
Ordinary nylon line with a barbless hook or hooks is commonly used in both Malaysia and Thailand for catching this prawn from rivers. Earthworms, small shrimps and small pieces of baked coconut are some of the favourite baits used. A small sinker is tied about one foot above the hooks, and the baited hooks are allowed to lie on the bottom. When a bite is detected, a few seconds must be allowed for the prawn to hold fast to the bait and hook; the line is then drawn up steadily, without jerking. Specimens caught are kept temporarily in submerged wire cages to ensure their healthy condition.
At night, prawns tend to move into shallow water to feed. When the water is clear a strong torch will reveal the characteristic bright pinkish reflection of their eyes, and specimens momentarily stupified by the bright light can be caught with a hand-net drawn from tail to head.
Young prawns are often present in considerable numbers below dams. At night, many of them will climb up and cling to the wet wall, and they can be collected with a simple hand-net.
Living specimens can be transported for a considerable distance in large tanks provided with aeration or continuous water circulation. For long journeys, specimens can be transported in plastic bags with oxygen, provided that the sharp tip of the rostrum of the larger specimens is cut off to prevent puncturing the bag. Prawns can be safely carried for three or four hours in shallow open fish containers, with water just deep enough to cover the specimens. They will also survive for several hours in bamboo baskets, packed between layers of moistened moss or soft aquatic plants, provided that small amounts of water are sprinkled into the basket at frequent intervals.
When berried females are not available from natural sources, spawning under controlled conditions becomes necessary. One pair will spawn in an aquarium of about 60 l capacity, while group spawning requires a large tank or trough.
Mature healthy males are kept separately, one in each tank. Several mature females may be kept together in one large tank, but every newly moulted ripe female should be promptly screened off from the rest to prevent it from being attacked while her new shell is still soft. Two or 3 h after moulting, when the new shell is fairly hardened, she is introduced into one of the male tanks. Mating will take place within a few hours, followed by egg-laying within 24 h.
For group spawning, a tank of about 1 m × 2 m and 40 cm high can hold about 10 specimens, and a trough of 1½ m × 3 m and 40 cm high about 24 specimens. One male to 4 to 5 females is a good ratio for spawning purposes. Newly-moulted sexually-ripe females are promptly attended by the males present, and mating and egg-laying take place without trouble.
All the spawning tanks and troughs should be provided with efficient aerators. A few days after egg-laying, the berried females should be transferred into hatching tanks.
Berried females, either collected from their natural habitats or mated and spawned in the hatchery, should be kept separately, one in each tank of about 50 to 60 1. During the whole incubation period the water of the hatching tank should be kept clean and well aerated.
As soon as the colour of the eggs starts changing from bright orange to light grey, it is advisable to add enough seawater gradually to the tank to raise the concentration to about 5 percent seawater. Although eggs will hatch well in freshwater, the presence of a small amount of seawater seems to provide a better medium for hatching and for the new hatchlings to live in.
3.1 Facilities and equipment
For experimental purposes, aquaria, ordinary plastic basins and shallow earthenware pots serve well as containers for rearing larvae. Aquaria of about 60 1 capacity, basins of about 30 cm in diameter and pots of about 60 cm are convenient sizes.
For large scale rearing of larvae, cement troughs, 50 to 70 cm × 2 to 3 m and 25 cm high are suitable. The bottom should slope slightly and end in a shallow collecting pit at the deeper and (water outlet end). Twin troughs are more economical to construct than single ones.
Sets of 4 cup-shaped strainers, made of nylon, silk or stainless steel, of different mesh sizes ranging from 25 per cm to 7 per cm, are required for the preparation of food for the different larval stages. Strainers of 12 to 14 cm in diameter are convenient.
Air compressor, pipes, air stones, water agitators, hydrometer, siphons, hand-nets, rubber tubing and other general aquarium equipment are also required.
Freshwater from rivers, streams, lakes and ponds should be filtered before using. Tap water (city water), which is usually highly chlorinated, should be seasoned for 3 to 4 days before use.
Seawater may be collected at high tide and should be filtered before using.
It has been found that artificial seawater prepared from rock salt (crude salt) is unsuitable, but that reconstituted from whole salt (evaporated from filtered sea-water) works fairly well.
3.2 Living and prepared foods for larvae
Minute zooplankton, such as cyclops, copepods and other small entomostracans can be collected with a fine-meshed conical net. Nauplii of Artemia can be hatched from the egg very easily in 30 to 40 percent seawater in trays or basins. Young Artemia can also be reared in tanks and pots as food for late stage larvae.
Of the various organic materials that are suitable for making into larval food, flesh of fish and shell-fish, steamed egg custard, fish-balls and fish eggs have been found to be the most practical. They are easily available and particles of suitable size can be prepared without difficulty. Flesh of fish is first chopped finely with a heavy kitchen knife, or broken up by passing through a meat grinder, then washed with several changes of clean water to remove soluble matter. The food particles are then graded by passing them through strainers of different mesh-size.
Steamed egg custard is prepared by beating together the yolk and white of hen's egg, a little water is added, then it is cooked in a double-boiler at a low temperature. Small amounts of yeast powder, vitamins or any other substance can easily be mixed with the egg material before it is cooked. The steamed egg is then broken up into small pieces and graded with the strainers into different sizes as above.
Fish balls are made by pounding fish flesh very thoroughly into a paste, which is then made into a small ball and cooked. It is available from the local markets and can be made into particles of different sizes by the method described above. Fish balls are convenient and economical to use, and contain very little soluble matter.
Fresh ripe fish eggs are also well liked by the prawn larvae. Fish roes are frequently available from the local food markets. Ripe eggs can be separated from the ovarian tissue in a bowl or basin with clean water. The eggs are then washed with several changes of clean water before using. Very small eggs are suitable for early larvae and larger ones for more advanced stages.
3.3 Technique and rearing procedure
There is seldom any problem in hatching the eggs if the berried female is kept undisturbed in well aerated water, and, normally, the larvae pass through their first and second stages with little loss. To rear Macrobrachium through all its larval stages, however, requires careful attention to correct feeding, and immaculate cleanliness is necessary to maintain optimum water conditions and to avoid the introduction of enemies and disease.
It has been observed that newly hatched larvae are highly euryhaline and can tolerate a wide range of salinity, but larvae show signs of distress from sudden increase or decrease in salinity. When transferred directly from the hatching tank to water of higher salinity (up to 50 percent sea water) they appear to be highly irritated for a minute or two but soon recover without marked after-effect. The following procedure of transfer of larvae from hatching tank to rearing trough has been found to work well.
The larvae are transferred soon after the whole batch of eggs has hatched. They are induced to concentrate at one end of the hatching tank by shading the rest of the tank with dark cloth or paper. Many of the larvae can then be taken out with a dipper or cup, and the remainder are siphoned out. These are then added slowly and gently to a clean rearing trough, filled to about 2/3 its final level with water of salinity similar to that of the hatching tank (about 1.7‰). A measured amount of filtered sea water is put into a bucket hung above the trough and slowly siphoned into the trough through small-bore rubber tubing, until a salinity of about 12‰ (approx. 35 percent sea water) is reached.
The water in the rearing troughs should be maintained at a salinity of 12 to 14‰ (about 35 to 40 percent sea water), a temperature of 24 to 30°C (optimum range 26 to 28°C) and a pH of 7.0 to 8.0. An aerator and a stirrer keep the water in constant motion and almost saturated with oxygen. The depth of water is 16 to 20 cm.
To avoid pollution, unfinished food particles, larval faecal waste and other undesirable substances that settle to the bottom should be removed by siphoning twice a day.
A partial change of water may be made by concentrating the larvae in one part of the tank or trough by shading the other parts. Water is then siphoned from the shaded part and replaced by new water of the proper salinity. When a complete change of water is required, the larvae are concentrated as before and removed to plastic basins. They are put back again when the rearing tank has been drained, cleaned and refilled with new water.
When a rearing trough is well managed no complete change of water is necessary throughout the entire rearing period, but a partial change is desirable at about 10-day intervals.
3.4 Feeding
Artemia eggs can be hatched in separate basins, but for large-scale operations it is more convenient to hatch them in the rearing troughs. The Artemia eggs are placed in a hatching ring at the shaded end of the trough; hatched nauplii are attracted to the unshaded part where the prawn larvae are present, and the egg shells remaining in the ring can be removed easily. Artemia eggs should be placed in the hatching ring every day from the time of transference of the prawn larvae, so that nauplii are available as food from the second day until the larvae metamorphose. The quantity of Artemia eggs needed for a trough of about 60,000 larvae is approximately ⅓ teaspoonful daily for the first 3 to 4 days, gradually increasing to about 1½ teaspoonfuls per day when the larvae are 30 days old.
For prepared foods, freshness of material and cleanliness in its preparation are important. A new supply of steamed egg custard should be prepared every day. Particle size is important; food particles that pass through a strainer of 25 meshes per cm are suitable for larvae of 2 to 4 days, 20 meshes per cm for larvae of 5 to 10 days, 12 meshes per cm for larvae of 11 to 20 days, and 7 meshes per cm for larvae of over 20 days.
Feeding with prepared food can be started when the larvae are 2 to 3 days old and continued until their metamorphosis. The frequency of feeding is 3 times a day for the first 5 days, 4 times a day during the next 10 days, and 4 times a day plus once at night for the remaining period.
For convenience in feeding it is better to concentrate the larvae at one end of the rearing trough by shading. Food is then gently spread on the surface of the water with a medicine dropper. The action of aeration and the flow created by the water agitator help to keep the light food particles in suspension long enough for the larvae to catch them.
The amount of prepared food to use daily is approximately 30 percent of the total body weight of the larvae. During each feeding the practice is to add food slowly until most of the larvae are seen carrying food; after about 1 min a little more is added to ensure that every larva is fed. Sometimes a little additional food is added between two regular feedings.
3.5 Care of larvae
It has been observed that the larvae suffer considerably if the salinity is suddenly lowered. It is therefore important that the salinity of the rearing troughs should not fall below the desired level. The troughs should be protected from rain. Larvae should also be protected against exposure to direct sunlight and strong illumination.
Prawn larvae are sensitive to nicotine, smoking in the hatchery should therefore be prohibited.
Some Artemia nauplii should be maintained in the rearing trough all the time to avoid cannibalism due to hunger.
Late larvae often jump out of the water and may get stranded on the walls of the trough above the waterline. This stranding may be prevented by shading the sides of the rearing trough, to attract the larvae to the centre, and by the provision of a “deflector” (developed by the Hawaii Division of Fish and Game) which consists of a single strip of plastic mosquito screen, about 12 cm wide, glued to the walls of the rearing tank just below the waterline.
When larvae are ready to metamorphose it is necessary to place small branches, sticks or small stones at the bottom of the rearing trough for the juveniles to settle on and hide in.
3.6 Diseases and parasites
A fungal infection, resulting in very heavy mortality, may occur from time to time. Effective curative measures are still under development. It can be prevented by thorough cleaning and disinfection of all troughs and equipment, careful filtering of water before use, cleanliness in the preparation of food and avoidance of all possible sources of contamination. Infected larvae can be recognized by the presence of small opaque whitish patches, first at the tail and bases of appendages, then spreading to the whole body. Infected larvae should be removed and destroyed. If a large percentage of the larvae in a trough have been infected then it is better to sacrifice them all.
Serious protozoan infection may also sometimes occur. Once the infection starts it may spread very rapidly and cause high mortality. Treatment with malachite green (0.2 ppm for ½ h daily), formalin solution (200 ppm for ½ h daily) and copper sulphate (0.4 ppm for 6 h, for severe cases repeat at 24 h intervals) have been recommended by Fujimura (1966).
4.1 Acclimatization to freshwater
When about 90 percent of the larvae have metamorphosed into juveniles, the remaining slower growers are transferred to another tank for further rearing and the juveniles are ready for acclimatization to freshwater.
When larvae are reared in an aquarium, basin or pot, a convenient way to acclimatize the juveniles is as follows: (1) siphon out about half of the water in the rearing container, (2) introduce freshwater slowly up to the original water level, (3) repeat the process 3 to 4 times at about 1½ h intervals (4) finally, drain the container almost completely and immediately let in freshwater to the desired depth. The whole process can be completed in 6 to 8 h.
When the larvae have been reared in a cement trough, the following acclimatization procedure for juveniles is adopted: (1) screen the water-outlet with fine-meshed nylon material, (2) introduce freshwater into the trough, close to the bottom, slowly but steadily, (3) when the water is almost entirely fresh, the juveniles may be transferred to juvenile rearing ponds. This process can be completed in 3 to 4 h.
4.2 Food and feeding
Suitable food for juveniles includes (1) living aquatic animals: small aquatic worms (Oligochaeta) and insect larvae (Chironomidae), (2) dried animal material: aquatic worms, earthworms, small crustaceans and insects, (3) fresh animal material: small pieces of earthworm, clams, snails, squids, shrimps and fish, (4) plant material: broken rice (unpolished) and other common grains, peas and beans.
Fresh animal material constitutes the principal food. Fresh fish, molluscs and earthworms need to be cut into small pieces, according to the size of the juvenile, and be given three times during the day and once at night.
Dried animal material is used to supplement the fresh diet. It is soaked in freshwater for about half an hour before use. Large pieces are cut into appropriate sizes. This food is given 2 to 3 times a week.
Living aquatic worms and chironomid larvae, when available, are given once a day, preferably in the evening.
Plant material is also used as supplementary food. Grains, peas, beans and soft aquatic plants are broken into small pieces when necessary and are given once every two days.
4.3 Management and care
Juveniles can be reared in the same trough as the larvae, provided they are not too crowded. However, for mass production, it is better to transfer them to juvenile rearing ponds (drainable mud ponds with cemented brick walls). A juvenile pond of about 5 m × 10 m × 40 cm high will accommodate about 10,000 juveniles. The water should be kept well oxygenated by aeration, and, if possible, a slow flow of water should be maintained. The water level should be maintained at a depth of about 15 cm. Pond water should be kept clean and all uneaten food should be siphoned out if possible.
Juveniles are vulnerable to attack by other juveniles during and immediately after moulting. Provision of small branches, gravel and large shells at the bottom of the rearing pond has been found to prevent high mortality from this cause. To minimize cannibalism, juveniles should be well fed, and small quantities of living aquatic oligochaets or chironomid larvae may be given from time to time in addition to those prescribed for regular feeding.
To prevent disease and parasitic infections, the rearing ponds should be completely drained, dried and disinfected before and after use. Methods of prevention and control of disease and parasites prescribed for larval stages (see section 3.6) are applicable here.
With good management and feeding juveniles are able to grow to young prawns of about 5 cm in the rearing pond within 60 days.
To set up and operate a hatchery to produce annually about 1 million young M. rosenbergii for stocking and culturing, the essential requirements are as follows:
5.1 Stock of mature prawns
Ten to 12 good berried females will be needed every month. In places where berried females are easily available from their natural habitats they should be collected at regular weekly intervals. Alternately, a stock of about 60 mature females and 12 males should be maintained in the hatchery. From this stock 10 to 12 females may be expected to breed every month. To ensure spawning efficiency, females should be discarded and replaced after their second spawning in the hatchery, and males should be replaced every three or four months.
5.2 Ponds and tanks
For maintaining the above breeding stock, three cement ponds, each measuring about 1½ m × 3 m × 40 cm deep, will be needed. Four aquaria, each measuring about 40 cm × 80 cm × 60 cm high, will be required as spawning tanks. A series of 16 to 20 aquaria, each of about 60 1 capacity, about 30 cm × 60 cm × 35 cm high, will be needed as hatching tanks.
Ten sets of twin cement troughs, each measuring about 70 cm × 3 cm × 25 cm high, will be required for larval rearing. Each trough can accommodate all the larvae (about 60,000) produced by one female at one hatching, and the same trough can be used for rearing 6 batches of larvae per year. Each batch is expected to produce on average about 10,000 juveniles.
For rearing juveniles, 20 ponds (brick walls and mud bottom), each measuring 5 m × 10 m × 40 cm high, are recommended. Each pond will take 6 batches of juveniles a year, each batch consisting of about 10,000 specimens.
5.3 Aeration and stirring systems
A reliable air-compressor, capable of supplying filtered air to all tanks and troughs at about 5 lb/in2 (360 g/cm2) pressure, together with the necessary pipes and lines, valves, air-stones and other accessories, is essential equipment that must be maintained in good condition all the time. A second air-compressor should also be installed as a standby. In addition to the air-compressor, about 6 aquarium aerators will be needed from time to time.
Each trough for larvae must be provided with a small water agitator to keep the water in constant motion.
5.4 Other hatchery equipment
A large refrigerator is required for holding a reserve supply of food.
Other items of equipment include hydrometers, salinity meter, pH meter, compressed oxygen cylinder, water analysis equipment, students' dissecting sets, a laboratory microscope, a binocular dissecting microscope, glass ware and a cooker.
5.5 Food
Approximately 5 gallons of brine shrimp (Artemia) eggs will be needed annually. These should preferably be vacuum packed in 1 gallon tins.
Supplies of local materials (fresh fish, eggs, etc) should be renewed at regular intervals to ensure their freshness.
5.6 Water supply system
Two water reservoirs, one for seawater and the other for freshwater, will be needed. The reservoirs should be not less than 1 m above the aquaria and rearing troughs, to ensure good gravity flow.
Different types of water pump, hose and pipelines are needed for seawater and freshwater. Four simple water filters (gravel/sand/charcoal filter) will be needed for filtering seawater and freshwater separately, before and after storage in reservoirs.
5.7 Staff
The staff required would consist of a manager, one trained technician, and four skilled labourers.
5.8 Hatchery building
One building, about 9 m × 24 m, will house the aquaria for spawning and hatching of eggs, the breeding-stock ponds, the larval rearing troughs, air-compressor, refrigerator, work benches and tool stores.
A simple building, with the main parts of the walls made of strong metal screens, will be suitable for the purpose. A suggested floor plan is given in Fig. 1.
The juvenile rearing ponds would occupy a space of about 25 m × 35 m. These should be protected from rain and direct sunlight, but need not be totally enclosed.
Prawns about two months after metamorphosis, measuring about 5 cm from tip of rostrum to tip of telson, are suitable for culturing. Young prawns collected from their natural habitats are quite suitable for culturing, but their supply is seldom dependable. A constant supply in large numbers can usually only be obtained by rearing them from the larvae.
Young M. rosenbergii are able to live well in varied types of fresh and slightly brackish water, provided that it is fairly well oxygenated and is within the temperature range of 22 to 32°C. They can be cultured in ponds, mining pools, partitioned canals and irrigated padi-fields.
Fig. 1 Suggested floor plan for a Macrobrachium prawn hatchery.
6.1 Culturing in ponds
6.1.1 Ponds Fish-ponds, or any pool of not less than 400 m2 and over 50 cm in depth, can be used for culturing this prawn, but ponds of over 1,000 m2 and 1 to 1½ m in depth are more suitable and economical to operate.
In the preparation of ponds and pools for culturing prawns, the routine practice developed for culturing fish, including the installation of screened water inlets and outlets, eradication of predators, removal of excessive growth of aquatic plants, should be followed. It is desirable to have a gentle flow of water, either continuously or for a few hours daily, throughout the entire period of culturing.
Application of animal manure, such as cow dung, mixed with lime, is to be done monthly to promote growth of natural food. About 200 kg of cow dung mixed with 10 kg of lime will be sufficient for each ha of pond of medium fertility, each month.
6.1.2 Combination with fish This prawn may be cultured alone or in combination with suitable species of fish; the latter has proved to be more economical to operate. Fish suitable for this purpose are plant and plankton feeders, such as Hypophthalmichthys molitrix (silver carp), Aristichthys nobilis (big-head carp) Ctenopharyngodon idellus (grass carp), Catla catla, Labeo rohita, Trichogaster pectoralis, Trichogaster trichopterus, Puntius gonionotus, Mugil cephalus, Helostoma temmincki, Chanos chanos and Osteochilus hasselti. Food competitors such as Cyprinus carpio, Cirrhina spp, Pangasius spp, Carassius spp, are not suitable. Carnivorous or predatory species such as Ophiocephalus spp, Anguilla spp, Oxyeleotrix and Clarias should be strictly avoided.
6.1.3 Stocking rate The stocking rate for this prawn depends on the richness of the soil, conditions of water and also the kinds and numbers of fish expected to be cultured together. The following tables will serve as a general guide.
Prawns cultured alone
| Pond conditions | Stocking rate (prawns/ha) |
| Rich | 15,000 |
| Medium | 10,000 |
| Poor | 6,000 |
Prawns cultured in combination with fish
| Pond conditions | Stocking rate of fish | Stocking rate (prawns/ha) |
| Rich | Full | 5,000 |
| Half | 8,000 | |
| Medium | Full | 3,000 |
| Half | 5,000 | |
| Poor | Full | 1,500 |
| Half | 3,500 |
6.1.4 Food and feeding Small pieces of waste fish, molluscs, earthworms, offal of animals and fish, insects, silkworm pupae, broken rice, grains, spoiled padi and discarded fruits are all suitable as food. A diet consisting of about 75 percent animal material and 25 percent plant material is suitable as a daily supplement to foods which occur naturally in ponds. In a well fertilized and well managed pond, the natural food material produced in the pond constitutes the main source of food for the prawns, especially during the first 1 to 2 months of culturing. A daily supplement equal to approximately 5 percent of the total body weight of the prawns is sufficient. Half of this should be added in the morning and half in the late afternoon. It may be cast into the pond or placed in shallow feeding trays set along the sides of the pond.
6.1.5 Management and care Water inlets should be carefully screened to prevent the entry of young stages and eggs of predatory fish, and to retain the prawns. For the same reasons, the bunds of the pond should be inspected at frequent intervals and all breakages should be promptly repaired, especially during the rainy season.
Small patches of Ipomoea may be grown in the pond to provide shade and shelter for the prawns, as well as supplying some fodder for the animals and green vegetable for the culturists. However, the area occupied by the Ipomoea should not be more than one tenth of the total area of the pond. In shallow ponds, provision of branches of bamboo or woody plants at the bottom of the pond helps in providing shelter and hiding places for the prawns, especially during their moulting periods, and thus reduces the chance of cannibalism.
Heavy mortality of prawns may occur due to depletion of dissolved oxygen during the hot season, especially in rich and heavily stocked ponds. Prawns suffering from lack of oxygen tend to migrate to the edges of the pond, become progressively weakened and sluggish in movement and die if not rescued in time. Methods used for the prevention and control of mortality due to oxygen depletion in pond fish culture are applicable here. Since prawns are more susceptible to oxygen depletion than fish, control measures should be applied earlier.
Cultured under good pond conditions and with an ample supply of rich food, young prawns of about 4 to 5 cm in length and 1 to 2 g in weight are able to grow to about 20 cm, weighing about 100 g, in 5 to 6 mo. Two crops of prawns can therefore be cultured in 1 yr when the ponds are well managed. Harvesting can be done either by draining the pond or by seining.
6.2 Culturing in padi-fields
Irrigated padi-fields that are able to retain a depth of water of not less than 12 cm throughout the padi-growing period (about 4 mo) are suitable for stocking with young prawns.
The bunds of the padi-field should be slightly raised and its water inlets and outlets properly screened to prevent escape of prawns and entry of predatory fish. The water-inlet-screen should be strong and high, about 1 ft higher than the water surface, to prevent prawns from climbing over and escaping.
One or two small sump-pits, each of about 1 m × 2 m and 50 cm deep, should be constructed at the lower end of the field, close to the water outlets, for reception of prawns when the field is drained.
Young prawns should be introduced into the padi-field when the transplanted padi seedlings are fairly well rooted. A stocking rate of 1 young prawn to every 10 m2 is recommended for padi-fields of average fertility. No supplementary feeding is necessary.
For stocking in padi-fields, prawns of over 3 mo old, about 6 to 7 cm in length, are preferred. Such prawns will be able to grow almost to maturity by the end of the padi growing period.
Prawns should be harvested at the time when the field is drained prior to padi harvesting. As the field is drained slowly, most of the prawns will retreat gradually to the lower end of the field and finally into the sump-pits, which still retain a certain amount of water when the field is completely drained. A short-handled hand-net is a convenient tool for fishing out the prawns from the sump-pits.
Prawns can be cultured in padi-fields together with fish such as Trichogaster pectoralis, T. trichopterus and Puntius gonionotus, which feed on plants or plankton.
Apart from the kinds and quantities of fertilizers normally used for padi cultivation, additional application of fertilizer is usually not required, and no supplemental feed is needed.
Since prawns are very sensitive to chemical insecticides, stocking of prawns is not recommended for padi-fields where such insecticides are normally applied.
Fujimura, T., 1966 Notes on the development of a practical mass culture technique of the giant prawn Macrobrachium rosenbergii. Paper presented to the Indo-Pacific Fisheries Council, 12th session, IPFC/C66/WP47
Ling, S. W., 1969 The general biology and development of Macrobrachium rosenbergii (de Man). FAO Fish. Rep., (57) vol.3:589–606
Acknowledgments
The author wishes to express his gratitude to Mr. Soong Min Kong, Director of Fisheries, Malaysia, and his senior Fisheries Research Officer for their deep interest and enthusiastic support for this project, to Mr. A.B.O. Merican, Fisheries Research Officer (Inland), and other members of the prawn working team for their close cooperation and zealous participation in this work, and to all FAO colleagues and friends who have contributed valuable advice and assistance, either directly or indirectly, in making the smooth and rapid progress of this work possible.
