III-VIII/R-2
FEEDS AND FEEDING OF WARM-WATER FISHES IN PONDS IN ASIA AND THE FAR EAST

by

S.W. LING
FAO Regional Office
Bangkok, Thailand

Abstract

To produce food as economically as possible, the centuries-old art of fish culture in Asia and the Far East has been developed on the basis of using a number of compatible non-predatory fish species that are able to make the best use of all natural food.

Supplementary feeding is practised for rapid growth of fish and for permitting high intensity of stocking.

Green manure and animal manure are the principal fertilizers used for the promotion and maintenance of a rich growth of natural food.

Artificial feeds used include a large variety of materials of both plant and animal origin, which can be obtained easily either without cost or cheaply. Chemical composition and food quotients of the principal kinds of feed are listed.

Rearing of fish fry and fingerlings is always done with great care to provide a rich supply of natural food and the daily application of supplementary feeds. Young fry of all pond fish of this region require high amounts of animal food.

Success in Chanos culture depends mostly on the maintenance of a rich supply of natural food: principally filamentous blue-green algae and diatoms.

Large fresh-water ponds with small fish populations are seldom fertilized and supplementary feed is very rarely given. In ponds of medium size with varied intensity of stocking, treatments range from no fertilizing and no supplementary feeding to heavy fertilization and heavy feeding, with many gradations in between. In ponds with high intensity of stocking, especially when several kinds of fish of different food habits are cultured together, heavy fertilization and ample supplementary feeding are always practised. Intensive feeding with artificial feed alone is done only in small ponds, mostly with running water, with extremely high stocking intensity.

L'ALIMENTATION DES POISSONS EN ETANGS A TEMPERATURE ELEVEE EN ASIE ET EN EXTREME-ORIENT

Résumé

Pour assurer une production alimentaire aussi économique que possible, l'art séculaire de la pisciculture est pratiqué en Asie et en Extrême-Orient selon un système qui associe diverses espèces compatibles et non prédatrices, aptes à tirer le meilleur parti possible de tous les aliments naturels.

Une alimentation d'appoint est fournie lorsque l'on veut accélérer la croissance des sujets d'élevage et maintenir une forte densité d'empoissonnement.

L'engrais vert et le fumier animal sont les principaux moyens utilisés pour favoriser une croissance abondante d'aliments naturels.

Pour l'alimentation artificielle, on puise dans une large gamme de produits, d'origine tant végétale qu'animale, qu'il est facile d'obtenir à peu de frais ou gratuitement. La composition chimique et le quotient nutritif des principales sortes d'aliments sont indiqués.

Lors de l'élevage des alevins et des jeunes poissons, on prend toujours grand soin de leur fournir une alimentation naturelle abondante et une ration quotidienne d'appoint Les alevins de toutes les espèces de poissons élevés en étangs dans cette région exigent une forte quantité d'aliments d'origine animale.

L'élevage du Chanos ne peut s'effectuer avec succès qu'à condition d'assurer une grande abondance d'aliments naturels, notamment algues bleues filamenteuses et diatomées.

Les grands étangs d'eau douce à faible densité de peuplement sont rarement traités aux engrais et il est tout à fait exceptionnel que l'on y déverse des aliments d'appoint Dans les étangs de taille moyenne, où la densité d'empoissonnement varie, les pratiques sont multiples : dans certains on n'ajoute ni engrais ni aliments supplémentaires, tandis que d'autres reçoivent de fortes doses d'engrais et d'aliments artificiels; enfin, entre ces deux extrêmes, on observe toute une variété de traitements. Dans les étangs fortement peuplés, notamment là où sont élevées ensemble plusieurs espèces de poissons ayant des habitudes alimentaires différentes, on a toujours recours à une fertilisation importante et à une abondante alimentation d'appoint. L'alimentation intensive, à base uniquement de nourriture artificielle, ne se pratique que dans les petits étangs, en général à eau courante, ayant une densité d'empoissonnement extrêmement élevée.

ESTUDIO SOBRE LOS ALIMENTOS Y LA ALIMENTACION DE LOS PECES DE AGUAS TEMPLADAS EN LOS ESTANQUES DE ASIA Y EL LEJANO ORIENTE

Extracto

Con objeto de producir alimentos lo más económicamente posible, el arte milenario de la piscicultura en Asia y el Lejano Oriente se ha desarrollado basándose en el empleo de cierto número de especies piscícolas no predatorias compatibles entre sí y capaces de aprovechar bien todos los alimentos naturales.

Se lleva a cabo una alimentación suplementaria para que los peces crezcan rápidamente y obtener una elevada densidad de población.

Los principales fertilizantes que se emplean para el fomento y conservación de un rico crecimiento de los alimentos naturales son el abono verde y el de origen animal.

Los alimentos artificiales empleados comprenden una gran variedad de materias de origen vegetal y animal, las cuales se pueden obtener con facilidad, sin gastos o a bajo costo. Se indica la composición química y los cocientes alimentarios de las principales clases de alimentos.

La cría de los jaramugos y de los pececillos se hace siempre con el mayor cuidado para facilitar un suministro rico de alimento natural así como la aplicación cotidiana de alimentos suplementarios. Los jaramugos de todos los estanques piscícolas de esta región exigen grandes cantidades de alimento de origen animal.

El éxito del cultivo de Chanos depende, sobre todo, de la conservación de un rico suministro de alimento natural: principalmente algas filamentosas verde - azules y diatomeas.

Los grandes estanques de agua dulce en los que viven pequeñas poblaciones piscícolas, se fertilizan pocas veces y muy raramente se da un alimento suplementario. En los estanques de tamaño con una intensidad variada de población, los tratamientos comprenden desde el no fertilizar y no dar alimentación suplementaria hasta una gran fertilización y una gran alimentación suplementaria, con amplias gradaciones. En los estanques con intensidad elevada de población, especialmente cuando se cultivan juntas varias clases de peces de diferentes hábitos alimentarios, se practican siempre una gran fertilización y una amplia alimentación suplementaria. La alimentación intensiva, exclusivamente con alimentos artificiales se hace sólo en pequeños estanques, en su mayoría de agua corriente, con una intensidad de población extremamente elevada.

1 INTRODUCTION

Fish culture in Asia and the Far East has a history of over 2,000 years and has been developed, with few exceptions, on the basis of using an association of a number of compatible non-predatory fish of different but complementary food habits, cultured together to make the best use of all the natural food material present in the pond. To accelerate fish growth, and also to permit increased stocking rate, many kinds of supplementary feeds are used.

Techniques for intensive feeding have been developed and applied in extremely heavily stocked ponds where the growth of fish depends entirely upon artificial feed, and the ponds serve merely as holding places for the fish.

Research on (i) the application of various types of fertilizers for promoting growth and increasing production of natural food, (ii) analyses of chemical composition and food value of various artificial feeds, (iii) feeding experiments, etc. have been conducted by many of the countries of this region. However, the exact dietary requirements of many of the common pond fish are not well known, and there is little scientific information on how to promote and maintain a rich growth of natural food. Study is also needed on the optimum amounts of food, both natural and artificial, required for maintenance and growth by different species of pond fish at different stages in their life history, intensities of stocking, and under varied environmental conditions.

2 FISH FOOD

2.1 Natural food

Since fishes of different food habits are cultured, practically all the plants and animals that grow naturally in the pond, except some of the tougher higher plants and large vertebrate animals, can be consumed as natural food. To promote growth of natural food, application of green manure, animal manure, agricultural by-products and, recently, inorganic fertilizers are used.

Green manure includes all types of tender plant leaves and stems that are rich in protein, such as odoriferous plants and legumes, that can either be collected from the field without cost or can be obtained very cheaply. Agricultural by-products include rice bran, soybean cake, oil-seed cake, grain husks, paddy straw, bean pods, etc. Animal manure includes cow dung, pig dung, goat dung, chicken droppings, duck droppings, silkworm droppings, human night soil, etc. In some cases animal sheds and fowl coops are built on the banks, or close to fish ponds so that the droppings can be washed into the ponds daily.

2.2 Artificial feeds

A large number of materials of plant and animal origin have been used as artificial feed. The criteria for the selection of artificial feed are (i) acceptability to fish, (ii) effectiveness in promoting fish growth and (iii) degree of cheapness and availability.

2.2.1 Feeds of animal origin

These include aquatic earthworms, land earthworms, clams, snails, daphnids, copepods, Mysis, small shrimps, small crabs, insect larvae, locusts, silkworm pupae, white ants, midges and other aquatic insects, trash fish, fish meal, fish entrails, entrails from slaughter house and food processing plants, meat, blood, liver and spleen, etc. Certain amounts of animal manures used as fertilizers are always consumed by fish directly as food.

2.2.2 Feeds of plant origin

These include green fodder such as Ipomaea reptans, land grass, sweet potato leaves, tapioca leaves, bean leaves, banana leaves; roots such as sweet potato, potato, tapioca; seeds such as peanuts, soybean, broad bean; cereals such as rice, wheat, barley, oats, maize and their bran, flour and meal; meal and oilcake of peanut, cotton seed, mustard seed, coconut; soybean milk, soybean refuse, mill sweepings, brewer's refuse; aquatic plants such as Wolffia, duck weeds, Spirodela, Azolla, Salvinia, Eichhornia, Pistia, Hydrilla, Najas, Potamogeton, Myriophyllum, Ceratophyllum; algae such as Oscillatoria, Lyngbia, Phormidium, Spirulina, Chaetomorpha, Entermorpha, Gracilaria, etc.

2.2.3 Chemical composition and food quotient

The chemical composition (percentage of protein, fat and carbohydrate) and food quotient of some of the common artificial fish feeds are given in Tables I and II.

3 FOOD AND FEEDING

Three main categories of fish culture operations are practised in this region:(i) those that depend on natural food entirely, (ii) those that depend on both natural food and supplementary feeding, and (iii) those that depend entirely on intensive feeding of food introduced from outside the pond.

Generally speaking, the first category includes ponds of large size of over four ha (except milkfish¹ ponds), such as converted farm-water reservoirs, converted small swamps, bunded shallow areas of lakes or coastal flats, converted mining pools, rice fields, etc; the second category includes ponds of medium size heavily stocked with fish; and the third includes ponds of small size, mostly provided with running water, and always extremely heavily stocked with fish.

The growth of natural food in large ponds depends on the nutrients present in the pond soil and those carried in by the water, and fertilizers are applied occasionally, if used at all. A rich supply of natural food in ponds of the second category is maintained by heavy application of fertilizers at regular intervals. No fertilizer is used for ponds of the third category.

¹ Chanos chanos

3.1 Rearing of fry and fingerlings

Rearing of fish fry and fingerlings has been developed into an industry in many countries of this region. Nursery ponds are carefully managed and well fertilized to produce rich growths of natural food, and supplementary feed of one kind or another is always given.

3.1.1 Culturing milkfish fry and fingerlings

Milkfish fry when collected from natural waters are delicate post-larvae of minute size. They are first kept for a few days in well protected “baby boxes” and are fed with either mashed hard boiled egg yolk, wheat starch or fine rice bran; then transferred to well prepared nursery ponds in which a rich growth of benthic micro-organisms, including blue-green algae, diatoms, protozoans, rotifers and other minute invertebrates has already started.

The fry feed readily on the minute natural food. When the supply of natural food is insufficient, fine rice bran, dried “lab-lab” and sometimes dried and ground submerged plants are used as supplementary feed, given either once or twice a day.

Table I

The composition of some supplementary feeds for pond fish

Table II

Food quotients of some supplementary fish feeds

Table III

Principal natural foods of Chinese carp fry

3.1.2 Culturing fry and fingerlings of Indian carps ¹ in India and Pakistan

Small seasonal ponds are generally used as nurseries. The pond bottom is dried, ploughed, levelled and then well fertilized and refilled with water. In a nursery pond of 0.4 ha, 3,125,000 fry can be reared for 12–15 days. The rich plankton produced provides the necessary natural food. Early fry prefer zooplankton. Rice bran, coconut oil-cake, mustard oil-cake and groundnut oil-cake, are often used as supplementary feeds. The oil-cakes are always given in finely powdered form.

Fry fed on oil-cakes in quantities not exceeding the following grow very well:

¹ Catla catla, Labeo rohita, and Cirrhina mrigala

3.1.3 Culturing of fry and fingerlings of Chinese carps ²

This is usually divided into two separate operations: (i) rearing of young fry to advanced fry, and (ii) rearing of advanced fry to advanced fingerlings.

3.1.3 (i) Rearing young fry to advanced fry

The average fry pond unit in China is about 1,000 m² in area and 0.8 m in depth. The prestocking preparations for each unit include (a) removal of surplus rich mud from the pond bottom, (b) sun drying the pond bottom, (c) application of quick lime (about 120 kg), (d) application of green manure (about 450 kg) and organic manure (cow dung 500 kg). Stocking is carried out after the caustic action of lime is completely over and a rich growth of natural food has developed.

To maintain a rich supply of natural food, an application of green manure (about 100 kg) and cow dung (about 30 kg) is made at about three-to five-day intervals. Supplementary feeds such as soybean milk, peanut cake, rice bran, etc. are given two to three times a day.

For rearing a batch of 150,000 fry, from young fry stage (averaging 0.8 cm/3 mg) to advanced fry (averaging 3 cm/lg) would take about 25 to 30 days. This would require a total amount of about 100 kg of soybean for making soybean milk as the principal supplementary feed or about 200 kg peanut cake if this is used. Soybean milk and peanut cake are often used together in various proportions according to personal preference of the farmer.

3.1.3 (ii) Rearing advanced fry to advanced fingerlings

Among the many types and variations practised, the method popular in Hong Kong is used as an example.

The prestocking preparation of the nursery pond is similar to that described above for rearing young fry. Peanut cake is used as the principal supplementary feed, and sometimes rice bran or soybean cake is also used.

A good nursery pond in Hong Kong has an average area of about 1,400 m² and one m depth, in which 50,000 advanced fry of three cm length can be stocked. It takes about 35 to 40 days for them to grow to 12 cm length (average wt 15 kg).

Rearing a batch of 10,000 fry of three cm size (total wt 10 kg) to advanced fingerlings of 12 cm (total wt 150 kg) will take about 40 days, and will require a total amount of about 150 kg of peanut cake. The daily amount of peanut cake used starts with about 1.5 kg and gradually increases to about 5 kg at the end of the rearing period.

² Ctenopharyngodon idella, Hypophthalmichthys molitrix, Aristichthys nobilis, and Cirrhina molitorella

3.2 Culturing fish in brackish-water ponds

3.2.1 Culturing milkfish

The milkfish feed mainly on filamentous blue-green algae (Cyanophyceae) and diatoms, (Bacillariophyceae). The blue-green algae eaten include Oscillatoria, Lyngbya, Phormidium, Spirulina, Microcoleus, etc. and the diatoms include Navicula, Pleurosigma, Mastogloia, Stauroneis, Amphora, Nitzschia, etc. A very rich growth of these algae occurs at the bottom of a good pond, forming a thick mat.

The filamentous green algae, Chaetomorpha, have a high food content, but when fresh these are relatively coarse and difficult to digest, therefore they are of little food value to the milkfish, especially to the fingerlings and young stages. However, after death and when softened by partial decomposition, Chaetomorpha detritus becomes good food for Chanos.

In Taiwan ponds when a rich growth of bottom algal pasture is maintained supplementary feed is only occasionally given. But supplementary feed, mainly rice bran, is always given when the bottom algal pasture is either insufficient for the fish, or is decreasing rapidly due to mismanagement or changes in environmental conditions.

In the Philippines, where ponds have less rich bottom algal pasture, supplementary feed such as rice bran is given. Algae collected from other water areas, the agar seaweed (Gracilaria), and even partially decomposed and softened common aquatic plants and paddy straw, are often used for feeding the fish.

In Indonesia rice bran is commonly used as supplementary feed.

3.2.2 Culturing grey mullets¹

Grey mullets are cultured either in fresh-water ponds or in brackish-waters of low salinity. Their natural food consists mainly of unicellular and filamentous algae, diatoms, benthic algae, detritus and small pieces of soft vegetable matter. Small quantities of rice bran are generally used as supplemental feed in India and the Philippines. In Hong Kong and Taiwan ponds, where heavy stocking is done in combination with Chinese major carps, intensive feeding is practised mainly with rice bran and peanut meal, and sometimes with fine pieces of well soaked soybean cake. When pig manure and night soil are used for fertilizing ponds, some of this is consumed directly by the fish as food.

In a heavily stocked pond in Hong Kong the average stocking rate per ha of pond is about 10,000 mullets and 1,500 Chinese carps. An average of 3,500 kg net gain in fish weight can be expected in a growing period of 300 days. To produce this amount of fish the quantity of supplementary feeds necessary is about 2,500 kg of rice bran and 3,000 kg of peanut cake, besides the repeated application of animal manure at three to five day intervals. The feeding schedule for such a one ha pond is as follows:

¹ Mugil cephalus and other species of Mugil

3.2.3 Culturing prawns

In the Philippines and Taiwan, various species of penaeid prawn, P. monodon, P. japonicus, P. indicus, Metapenaeus ensis, etc. are cultured together with milkfish in brackish-water ponds. These prawns feed mainly on the worms and insect larvae which occur abundantly in the ponds but are not eaten by the milkfish. No supplemental feeding has yet been practised.

3.3 Culturing fish in fresh-water ponds

In Taiwan, as well as in other countries, fish ponds of over four ha, such as the reservoir fish ponds, are very seldom fertilized and no supplemental feed is given. Fertilizers are used in ponds below two ha, and feeding is done when stocking intensity is high.

The Chinese carps (grass carp, silver carp, bighead carp, mud carp), common carp (Cyprinus carpio), carassius carp (Carassius carassius), mullet and milkfish are cultured in various combinations and ratios. Mono-culture is also sometimes practised.

Grass, aquatic plants, duck weeds, banana leaves, vegetable waste, bean leaves, rice bran, peanut cake, soybean cake, wheat bran, trash fish, offals, blood meal, fish meal, earthworms, silkworm pupae, etc. are the principal materials used as feed.

When grass carp is cultured in combination with other fish, fresh tender plant material is used intensively. Green fodder is given usually twice a day by placing it within a floating feeding ring made of three or four bamboo poles. The amount of feed given per day has been estimated to be about 15–20 percent of the total weight of the fish fed. The fish farmer usually gives the quantity of fodder that will last for about an hour after each feeding. Grass carp excreta are often consumed by other carps directly as food. Other feeds are given roughly in the order of 7,000 kg agricultural products and 2,000 kg of animal products per ha per annum in heavily stocked ponds.

Feeding schedule for culture of mixed species*
(one ha pond, for producing 3,500 kg net wt of fish)

* Stocking rate:- grass carp 250, silver carp & bighead carp 2000, mullet 3,000, milkfish 2,000, mud carp 1,000, common carp 500.

In mono-culture of common carp the feeding period lasts from February/March to November, and when mixed feed is used the proportion of plant to animal feed generally falls gradually from about 90 percent at the start to about 50 percent at the beginning of May. Pure animal material is then given from June until the end of August. Plant material is given again, increasing gradually from 50 percent at the beginning of September to about 90 percent about mid-November when feeding is discontinued.

For producing 1,000 kg of fish (net gain) about 1,500 kg of silkworm pupae or 7,000 kg of rice bran, or a mixture of 1,180 kg of pupae and 1,200 kg of rice bran is fed as follows:

Feeding schedule for mono-culture of common carp
(for producing 1,000 kg net wt of fish in one single harvesting)

The large specimens of carp from such a mono-culture may, however, be harvested at the end of each culture period, the rest being left in the pond for further growth. When using silkworm pupae as feed, the feeding schedule would be as follows:

Feeding schedule for mono-culture of common carp
(Harvested in three instalments)¹

¹ Pond size about 5,000 m²

In this case for 400 kg advanced fry stocked in February, the total harvest should be 2,400 kg, giving a net gain of 2,000 kg fish for 3,000 kg pupae used.

In Hong Kong, where grass carp, silver carp, bighead carp, common carp, mud carp, grey mullet (and sometimes black carp²) are stocked heavily in fresh-water ponds or ponds of very low salinity, heavy applications of fertilizers - green manure, animal manure and chemical fertilizers - are made for adequate production and maintenance of natural food. Intensive feeding is done with green fodders, vegetable wastes, aquatic plants, rice bran, peanut cake, soybean cake, sesame cake, wheat bran, etc., and when black carp is present snails, clams and earthworms are also used.

To maintain a constant daily supply of animal manure, which is also consumed by fish directly, ducks and pigs are kept in pens and sties built over or on the banks of the ponds. About 100 pigs (average size 30 kg) or about 2,500 ducks (average weight one kg each) are sufficient for producing animal manure required for one ha pond.

In Malaysia and Singapore there are two major types of fish culture, (i) using the association of Chinese carps, and (ii) using Puntius, Trichogaster, common carp and Tilapia.

For the first type, the feeds and feeding methods are very similar to those practised in South China, Taiwan and Hong Kong, but with more extensive use of animal manure. For the second type, feeds and feeding are also based on Chinese practise, but feeds of animal origin, except manure, are seldom used.

In Thailand also the culturing of Chinese carps is based on Chinese methods, but feeds used are mainly of plant origin, except in North Thailand where white ants are often used for feeding common carp. For Tilapia, Trichogaster, Helostoma, Puntius and Osphronemus, cooked rice bran, broken rice, corn meal, Ipomaea, duck weeds, aquatic vegetation and land fodders are used. Feeds for Pangasius consist mainly of mixtures of rice bran, cooked broken rice, chopped Ipomaea, aquatic vegetation and trash fish. The catfish, Clarias, is fed principally with trash fish and animal offal.

In the Philippines, although fish stocking is extensive, fish culture in freshwater ponds is not yet popularly practised. For feeding Ophicephalus and Clarias, trash fish and small shrimps are used, and for carps and other non-predatory fish, rice bran, peanut cake and green fodder.

In Indonesia where Puntius, Tilapia, Helostoma, common carp, Osteochilus, Chanos and Osphronemus are cultured in ponds or in the rice fields, (in most cases only to relatively small sized fish), the main emphasis is on the application of fertilizers for producing natural food. Supplementary feeds given are rice bran, peanut meal, coconut meal, aquatic plants and land fodder.

In Cambodia, Pangasius are fed with the same kinds of feeds used in Thailand.

In Vietnam, common carp are mostly fed with rice bran and peanut meal.

In India and Pakistan where a number of Indian carps are extensively cultured, the emphasis is on production of natural food by the application of green and animal manure. Rice bran, oil-seed cake and groundnut cake are the principal artificial feeds given. Where Chinese grass carp is cultured, a large variety of aquatic vegetation and green fodder is used.

In Ceylon, rice bran, coconut cake and groundnut cake are the main kinds of fish feeds.

In Mainland China, the common practice of intensive stocking and heavy feeding has been further developed. It has been reported that during recent years with increased stocking rate (repeated heavy stocking of different kinds of fish and of different ages at three months intervals) and very heavy feeding, the annual net production has reached 8,000 kg per ha for ponds 2.5 to 3 m deep.

Most of the feeds used are similar to those already described but prepared in the following ways:

1. Feeds of plant origin

   Soybean milk: It is important for feeding all kinds of fish fry and is made by soaking soybean in clean water for six to ten hours, then grinding the bean with water through a stone mill (one part soaked bean to 12 parts water), filtering off the residue and using the milk while fresh by sprinkling or spraying it into nursery ponds.

   Soybean cake: The residue left after oil has been pressed out of the beans is first broken into pieces, soaked in water and then broken into smaller pieces (for feeding omnivores), or ground into fine particles (for feeding plankton feeders). This is especially useful for feeding fingerlings.

   Soybean residue: The residue obtained in the preparation of soybean milk and bean curd, is fed to both fingerlings and big fish.

   Wolffia and small Lemna are used for feeding fingerlings of grass carp. They are sometimes specially cultured in fertile ponds or sections of canals for this purpose. Pistia, Eichhornia, and even Salvinia when chopped into small pieces are used for feeding grass carp and common carp. Alternanthera cooked and mixed with rice bran is well liked by all the major carps. Fresh rice stalks and leaves can be used for feeding grass carp of over one kg, smaller fish prefer finely chopped pieces; they also like pumpkin and potato stems and leaves.

2. Feeds of animal origin

   Fresh-water snail and clams, such as Viviparus, Bullacta, Corbicula and Anadonta are excellent feeds for black carp. They are always used fresh and for feeding fingerlings they are broken into fine pieces. For feeding yearlings small ones are used whole but large ones are broken, while for big fish whole specimens are used.

² Mylopharyngodon piceus

3.4 Intensive feeding

Examples of intensive feeding may be illustrated by (i) the growing of carps in small running water ponds in Japan, (ii) the culturing of eels in Japan and Taiwan, (iii) the culturing of Pangasius catfish in pens in Thailand and Cambodia and (iv) the culturing of Clarias catfish in Thailand. In all these cases the ponds or pens serve only as holding space while the growth of fish depends entirely on the feeds given.

3.4.1 Rearing carps in small running-water ponds in Japan

This is a well known system of fish culture practised in Japan, and has been fully described in many publications. Ponds are always built along-side or close by streams with an ample supply of good running water the whole year round. The pond is small, about 30–100 m², and either rectangular or triangular in shape. The bottom of the pond is smooth but sloping and is usually cemented and paved with small rounded pebbles; the sides are constructed of stones. The inlet and outlet are designed to allow the efficient control of waterflow from the stream through the pond.

A pond of 50 m² and 1.8 m deep may be stocked with as many as 10,000 fingerlings of the common carp, each weighing about 75 g, and in one growing season (about seven months), a total harvest of about 8,200 kg of fish can be expected, a net gain of 7,500 kg of fish from about 30,000 kg of feeds used.

The fish are fed 12 to 18 times a day, from 0500 hours to as late as 2200 hours, depending on the temperature of water and size of fish. The warmer the water and the larger the fish the more frequently they are fed. Feeds are given during the period when the water temperature is from 16° to 30° C; below 16°C no feed is given.

The growing season is divided into three periods, (i) about 100 days, from beginning of May to beginning of August (fingerlings); (ii) about 40 days, from beginning of August to mid-September (young fish), and (iii) about 70 days, mid-September to end of November (big fish).

For growing, in a running water pond 50 m², 10,000 fingerlings (average weight 75 g, total weight 750 kg) through one growing season of about 210 days, to produce a harvest of about 8,200 kg fish or a net gain of 7,500 kg, the kinds and amounts of feed given are as follows:-

3.4.2 Eel (Anguilla) culture in Taiwan

Eel ponds range in size from 800 m² to 2,000 m², (1 to 1.5 m deep). The bottom of the pond consists of mud, is smooth and slightly sloping. The pond walls are cement lined brick or stone. Water inlets and outlets are well planned and constructed to maintain a continuous flow of water through the pond.

Eel fry of an average weight of 0.2 g are collected from lower reaches of rivers by special traps. They are cultured in nursery ponds to young eels, and then from young eels to marketable size in growing ponds.

The growth rate is rather slow. It takes about one year to grow from fry of about 0.2 g to young eels of about 20 g, and a second year from young eels to marketable size of about 200 g each.

The stocking rate for eel fry is about 300 specimens (total wt about 60 g) per m² and that for young eels is three or four (total wt about 60–75 g) per m².

Feed consists of trash fish, small crabs and other crustaceans unsuitable for human consumption, offal from slaughter houses, fish markets and fish processing plants, ox blood, earthworms, aquatic worms and silkworm pupae. The feed (except worms and pupae) is chopped into small pieces. Worms are used fresh. Dried silkworm pupae are soaked in fresh water for an hour or so before use.

Eel fry are fed mainly with worms and fine pieces of cooked trash fish. Silkworm pupae are used mostly in the last stage of rearing and fattening only. Feeding is done twice a day at fixed times and places. Feed is placed in feeding baskets (shallow bamboo baskets with large mesh) which are hung submerged along the edges of the feeding platform.

The daily ration of feed given varies from 5–10 percent of the estimated total body weight of eels present, according to temperature of water; more is given when water is warm. The conversion ratio varies from 10–15:1, depending on the quality of trash fish and the quantity of crustaceans present.

3.4.3 Catfish (Pangasius spp.) cultured in pens

This is a popular practice in Thailand and Cambodia. The pens are mostly made of bamboo splits or ratten and are set floating along river banks or the sides of the floating houses, and in shallow places resting on the bottom.

The pens are roughly of three sizes: (i) small - about 1 × 2 m by 1 m deep, used mainly for rearing fry, (ii) medium - 2 × 5 m by 1.5 m deep, (iii) large - 2.5 to 4.5 m × 7 to 10 m by 1.5 to 2 m deep.

The stocking rate is roughly 2,000 fry for each small pen; 1,000 fingerlings and young fish for medium pen; and 1,500 to 3,000 fingerlings and young fish for large pens

Principal feeds are trash fish, broken rice, rice bran, corn and tender aquatic plants. Trash fish are chopped into small pieces and are given either fresh or lightly cooked. Corn grains are used after partial cooking. Broken rice is cooked, is mixed with rice bran, chopped vegetables and small pieces of fish and made into small balls.

Fish are fed two or three times a day, either by throwing the feed into the pen through its door or by placing it in a feeding tray hung submerged inside the pen.

The amount of feed given daily ranges between four and six percent of the weight of fish, depending on the amount of material available. The conversion ratio has been estimated to be roughly 8–10:1.

An ingeneous method is commonly adopted for detecting any breakage of the pen. A definite number of Clarias, usually about five or six, are put into the pen together with the Pangasius. Each feeding time the number of Clarias is carefully counted. When the Clarias are all present, it means all is well, but when some of them are missing it indicates that the pen is broken somewhere and repairs are made promptly to prevent escape of Pangasius.

3.4.4 Catfish (Clarias spp.) culture in Thailand

This is an unique fish culture operation that involves extremely heavy stocking and intensive feeding. A small pond of 400 m² and 2.5 m deep can be stocked with as many as 40,000 fingerlings (total wt 600 kg), and by intensive feeding, at the end of a five months growing period, 4,300 kg of fish can be expected - a net gain of 3,700 kg of fish from about 26,000 kg of feed.

Pond areas range from 100 to 1,000 m², and depths from 1.5 to 3 m. The water is turbid and rather stagnant, but with provision for introducing fresh water into the pond whenever needed. A small water pipe is sometimes installed at the center of the pond to create a low fountain.

Both Clarias batrachus and C. macrocephalus are cultured, generally separately, but sometimes together. The fish are usually harvested at a weight of 200 g. Stocking rates per m² of water surface, and length of culture period from stocking to harvest, are as follows:

The principal kinds of feed used are fresh trash fish, small dogfish, and slaughter house, fish market and fish processing plant offal. When these are in short supply, cooked broken rice is used instead. The feed is chopped into small pieces (depending on size of fish to be fed), mixed and used as fresh as possible. Feed intended for use some hours later, or the next day, is cooked.

The fish are fed twice during the day and once at night. Feed is given slowly, handful by handful, from a wooden platform, until most of the fish stop feeding. The daily ration of feed given is roughly about 6 – 8 percent of the body weight of the fish. The conversion rate has been estimated to be about 6–8:1.

Similar heavy stocking and intensive feeding, with similar kinds and quantities of feed, are also being adopted in rearing Pangasius fry and fingerlings in small mud ponds (sometimes as small as 5 m × 10 m by 1 m deep).