by
G. A. PROWSE
Tropical Fish Culture Research Institute
Malacca, Malaysia
Abstract
Traditional methods of fish-pond fertilization are reviewed. In China, Hong Kong, Taiwan, Singapore and Malaysia, Chinese carps are raised in conjunction with pigs and ducks. Cut plants and night soil are often added. In India where other carps are cultured, cut plants, oil seed cake and sewage are used as fertilizers. In brackish-water ponds of Taiwan, Philippines and Indonesia, cut weeds, rice bran, seed cake and manure are added as fertilizer and food. Experiments on artificial fertilizers have been carried out in Taiwan, Philippines and India, but have been based on N-K-P mixtures. In Malacca it has been shown that only phosphate fertilizer is needed in ponds, and this method is more economical in labour and costs.
REVUE DES METHODES DE FUMURE PRATIQUEES DANS LES ETANGS PISCICOLES A TEMPERATURE ELEVEE EN ASIE ET EN EXTREME-ORIENT
Résumé
La communication passe en revue les méthodes traditionnelles de fertilisation des étangs de pisciculture. En Chine, à Hong-Kong, à Taïwan, à Singapour et en Malaysie, les carpes chinoises sont élevées en association avec des porcs et des canards. Il n'est pas rare que l'on procède à des apports d'engrais flamand et de plantes coupées. En Inde, où d'autres carpes sont élevées, on se sert, comme engrais, de plantes coupées, de tourteaux d'oléagineux et d'eaux d'égoût. Dans les étangs à eau saumâtre de Taïwan, des Philippines et d'Indonésie, des plantes coupées, du son de riz, des tourteaux et du fumier sont déversés dans l'eau pour servir d'engrais et d'aliments. Des expériences ont été faites à Taïwan, aux Philippines et en Inde avec des engrais artificiels et notamment des mélanges de N-K-P. A Malacca, il a été prouvé que les étangs n'avaient besoin que d'engrais phosphatés et la méthode appliquée s'avère peu onéreuse tant en matière première qu'en main-d'oeuvre.
EXAMEN DE LOS METODOS DE FERTILIZACION DE LOS ESTANQUES PISCICOLAS DE AGUAS CALIDAS EN ASIA Y EL LEJANO ORIENTE
Extracto
Se pasa revista a los métodos tradicionales de fertilización de los estanques piscícolas. En China, Hong-Kong, Taiwan, Singapur y Malasia, se cría la carpa china conjuntamente con los cerdos y los patos. Con frecuencia se adicionan plantas cortadas y residuos fecales. En la India, en donde se cultivan otros tipos de carpa, se utilizan como fertilizantes plantas cortadas, tortas de semillas oleaginosas y aguas cloacales. En los estanques de aguas salobres de Taiwan, Filipinas e Indonesia se añaden como fertilizantes y alimentos plantas cortadas, salvado de arroz, torta de semillas y estiércol. En Taiwan, Filipinas y la India se han llevado a cabo experimentos de fertilizantes artificiales basados en mezclas de N-K-P. En Malaca se ha demostrado que solamente se necesitaban en los estanques abonos fosfatados y que este método es más económico en cuanto a mano de obra y costo.
Fish culture has been practised in many Asian countries for a very long time, in China for over two thousand years. Use is made of materials easily available and so methods may vary from place to place, particular methods sometimes being restricted to particular geographic areas. Migrating populations, especially the Chinese, have taken their methods of fish culture with them, not always to areas most suited to such methods. Underlying most traditional fish culture is the use of organic matter to fertilize the ponds, since it is only in recent years that inorganic fertilizers have become freely available.
In S. China the culture of carps (mainly Ctenopharyngodon idella, Hypophthalmichthys molitrix, Aristichthys nobilis and Cyprinus carpio) is often associated with pig rearing, and this is particularly true in Kwangtung province. Pig sties are built on the sides of the ponds and the manure and washings serve to fertilize the water. Night soil is often added and latrines are even built out over the water. In other parts duck rearing is coupled with fish culture, the duck pens being built out over the water surface to give the maximum fertilizing effect. Poultry droppings are often used as well. Where buffaloes and cattle are more plentiful their manure is often used to fertilize ponds, and the byres may be built close to the water. A certain amount of green manuring is practised, but more often cut grass, goatweed and other strong smelling weeds, and aquatic plants may serve directly as food for fish like the grass carp, or for invertebrates which in turn serve as fish food. The uneaten parts of the plants decay and may act as fertilizer. Tea-seed cake, often mixed with rice bran, is sometimes applied as a fish poison which later may have a fertilizing action. Rice bran, soybean meal and groundnut cake are given as food for the fish but may also serve as fertilizers. Sometimes there may be a rotation of green manuring followed by animal manuring during the growing period of the fish. With continued use of organic manures the pond bottom becomes elevated, and from time to time the ponds are drained and the muck scraped out and applied to land crops.
Information concerning the use of inorganic fertilizers in fish ponds on the Chinese mainland is lacking. With the vast agricultural problems and the huge population, it seems doubtful that inorganic fertilizers will be diverted from agriculture to fish culture.
Fish culture in Hong Kong and its allied territories, because of the proximity to Kwangtung, tends to follow the pattern in that province, particularly as so many of the immigrants come from that area. Where fattening of carps for the market is undertaken, a typical feature is the pig sties or cowsheds close to the pond edge. However, water difficulties have somewhat restricted this type of fish culture, and greater attention is given to the entrepôt trade in Chinese carp fry. The aim in fry holding ponds is to achieve only a maintenance ration for the fry, so excessive fertilisation with animal manures is not an advantage. Instead, green manuring may be practised, and some rice bran may also be given. In any case, with the high population pressure and the need to grow fresh vegetables on the limited area of land, animal manure is more in demand for land crops.
Some brackish-water ponds are maintained in Hong Kong, mainly culturing grey mullet (Mugil cephalus), but various carp species may be included as well. Although some manuring is practised, reliance is placed more on feeding with soybean flour, rice bran, groundnut cake and such foods, and these may also act as fertilizers.
A few preliminary experiments have been carried out on the use of inorganic fertilizers, but water difficulties have prevented these from being very extensive, and results are still inconclusive.
Fish culture in Taiwan has been largely concerned with brackish-water ponds using mainly Chanos chanos, although more and more fresh-water ponds are being constructed and may be expected to increase considerably in number with the spawning of Chinese carps in Taiwan. Buffalo, cattle, pig and various other animal manures, including night soil are used as fertilizers. Rice and wheat bran, tea seed, ground nut and soybean cake and Leucaena seed are also used, although some of these may also act directly as food for the fish. Usually about four lots of organic manure are applied in a growing season.
Inorganic fertilizers are now commonly used, usually N-P-K mixtures in the proportions 8-9-2 or 8-4-2, applied at the rate of 300–500 kg per hectare per annum. This dosage is stated to give a crop of fish equal to that achieved with twice the amount of rice bran or 30 times the amount of night soil. Unfortunately the experiments on which the figures are based lacked proper controls and no attempt was made to assess the effect of the different elements separately. It is by no means certain that the addition of potassium is necessary, and in fresh-water ponds it is possible that the addition of nitrogen may also be unnecessary.
Fish farming in the Philippines is still mainly concerned with brackish-water ponds involving Chanos chanos, but with hatcheries for fresh-water fish opened in various places fresh-water fish culture is spreading. In brackish-water ponds natural fertilization occurs when water is replenished by spring tides, thus bringing in a fresh supply of nutrients. In some areas tobacco dust is applied when the ponds have been filled with just enough water to cover the bottom. This acts as a fish poison against unwanted species of fish, and as it decays it serves as a fertilizer for the benthic algae. Rice bran and soybean flour are sometimes mixed with the tobacco dust to increase the fertilization effect. In other areas tea-seed cake may be used in a similar way. In both cases the ponds are stocked with fish as soon as there is abundant algal growth, by which time the toxic effect of the fish poisons has dissipated. In some areas green manuring with the leaves of certain leguminous plants is practised, the leaves being strewn over the pond bottom in the early stages of algal growth.
In fresh-water ponds cattle, pig and poultry manure have been used, but this is now giving way to the use of inorganic fertilizers.
The inorganic ferilizers used in both brackish and fresh water-ponds are N-P-K mixtures, usually in the proportions 16-20-0, 12-12-12, 12-24-12. In brackish ponds the algae are generally planted before fertilization, and the fertilizer applied at the rate of 20 g per cubic metre of water every fortnight until a heavy algal growth is achieved. Similar fertilizers are being tried in fresh-water ponds, although here the applications are given usually after fish have been stocked. Unfortunately the experiments on which the figures have been based lacked proper controls, and there was no proper assessment of the effect of the individual elements of the mixtures, so it is by no means certain that these proportions are the best.
The culture of Indian carps (mainly Catla catla, Labeo rohit a and Cirrhina mrigala) in fish ponds is an important industry, and various methods are used to fertilize the ponds, nearly all based on the use of organic matter. A common and simple method is by diverting sewage into fish ponds, and this is used as a means of sewage purification, notably in the Calcutta area. The possibility of oxygen deficiency in the fish ponds is a danger, but many Indian carp species have been found to stand quite low oxygen concentrations. Phenomenal crops of fish are claimed for sewage ponds, although the figures seem less impressive when critically analysed. Some experiments have been tried with very dilute sewage, with favourable results, and this suggests that sewage might be used more efficiently than it is at present.
Other materials used are cow dung stable refuse and poultry manure. Oil-seed cake is often given, theoretically as a food for the fish, but it probably acts mainly as a fertilizer. Green manuring is practised in some areas, bundles of cut grass and weeds being dumped in heaps on the bottom of the drained ponds, usually with stones or lumps of clay to hold them down. The placing of the weeds in heaps, rather than spreading them over the bottom, lessens the danger of deoxygenation of the water. Animal manures are often confined in baskets or bags for the same reason.
Inorganic fertilizers have come into use, there being no fixed method, since much of the work is still experimental. Research has tended to be centred on the use of N-P-K mixtures without adequate tests of the effect of the individual elements. This is a pity, because limnological data from many of the areas suggest that the addition of potassium is unnecessary, and with the prevalence of nitrogen-fixing bluegreen algae in so many parts of India, it seems distinctly possible that the addition of nitrogen is also unnecessary. Where phosphate alone has been used it seems to give crops as good as, if not better than, with the mixed fertilizers, but the lack of good controls in these particular experiments detracts from the value of their results.
In Indonesia there are both extensive brackish-water ponds, based mainly on the culture of Chanos chanos, and a considerable number of fresh-water ponds, in which the main species cultured are the common carp (Cyprinus carpio), Puntius gonionotus, Tilapia mossambica and the giant gourami (Osphronemus goramy). In brackish-water ponds green manuring is commonly practised, leaves of the mangrove (Avicennia) and rice straw being strewn over the bottom of the drained pond. In fresh-water ponds cattle, horse and cow dung are used, the manure usually being placed in a small bamboo enclosure in one corner of the pond to avoid general deoxygenation of the water. Sewage has been used in some ponds but not to the extent that it is used in India.
Although some initial experiments were started on the use of inorganic fertilizers, these have not been followed up to any great extent.
Both brackish-water and fresh-water fish ponds are maintained in Ceylon, and in both cases fertilization is largely through the agency of animal manures, although sewage is used to some extent. A certain amount of green manuring is also practised. More recently experiments have been carried out using ammonium phosphate as a fertilizer in brackish-water ponds and the results seem promising, although it is questionable whether the cost of this particular fertilizer would justify its use.
In East Pakistan farmyard manure, cow dung and horse dung are commonly used to fertilize fish ponds, the manure usually being confined in bamboo enclosures at the corners of the ponds. Sometimes a mixture of superphosphate and cow dung is applied, three parts dung to one part superphosphate, at the rate of 555 kg/ha per annum. Oil cake is frequently added, and where available slaughter house refuse and mill sweepings are often used. Green manuring is practised, a leguminous crop being grown in the pond before flooding, or cut weeds being placed in heaps on the bottom. Methods in West Pakistan are somewhat similar, although camel dung is also available.
There seems to have been comparatively little research on the use of inorganic fertilizers alone in fish ponds in Pakistan. Such methods of fertilization might be particularly useful in semi-arid regions where organic manures are at a premium, and which would be more advantageously used to provide humus to the soil.
Fertilization of fish ponds in Thailand, as in most other Asian countries, commonly involves the use of buffalo, cow and pig manure, and not infrequently night soil is added. In some areas pig sties are built close to the water's edge, while duck pens may be built out over the water. Cut vegetation, offal, rice bran, oil cake are all thrown into the pond, and while they may form food for the fish, they also may act as fertilizers. There have been a few experiments on the use of inorganic fertilizers, but as in other Asian countries these have been more concerned with N-P-K mixtures rather than with the individual elements.
Fish culture in these territories tends to fall into two main categories, the highly commercialised Chinese methods using Chinese carps, and the subsistence methods used by Malays, mainly involving “wild” fish. The Chinese system characteristically follows that of Kwangtung province, with pig sties built at the water's edge and latrines often built over the water. One or two farmers concentrate on duck breeding rather than pig rearing, and in their ponds the duck pens are built out over the water. Cut land plants such as tapioca, banana leaves, sweet potatoes, kangkong (Ipomaea repens), and sometimes rice bran are fed to the fish, and the undigested parts may also have a fertilizing action. Malays, being Muslims, are not permitted to rear pigs, so where fertilization of the pond is a practice buffalo and cattle byres are built near the water's edge, but more often than not the ponds are left unfertilized.
Research in Malacca, both in experimental ponds and commercial ponds, has demonstrated that inorganic fertilizers can be superior to organic manures, and that once a pond has been limed to neutrality only superphosphate need be added. Nitrogen fixation takes place through blue-green algae, which are stimulated by the addition of superphosphate. Studies on commercial ponds, and comparisons with ponds fertilized by superphosphate, have shown that the bulk of the algal production in commercial ponds is not digested by the fish and is virtually useless. This is why so much supplementary food has to be given. With superphosphate applications and no supplementary food, it has been demonstrated that as good, or frequently better, crops can be raised than in commercial ponds. Furthermore, it has been shown that overfertilization of ponds is possible, leading to autoshading of the plankton and a reduction of total plant production and dangers of oxygen deficiency; this may be part of the reason why commercial ponds only give good crops when there is considerable supplementary feeding. There is some evidence from Malacca that excessive supplementary feeding may in itself lead to excessive growth of surface plankton, autoshading and oxygen deficiencies. The research in Malacca has been carried out with proper controls and on a sound statistical basis. Because the method now recommended involves so little work (only 10 man days labour per year to apply the fertilizer) and the fertilizer is so cheap (Malayan $50 for the 333 kg/ha applied) it is gradually being adopted by commercial farmers, on estates and on Federal Land Development schemes. Results in most cases have been very encouraging.
Summing up, it would be true to say that while in Asia the common methods of fertilizing fish ponds utilize organic manures, more and more evidence is acccumulating that inorganic fertilizers are not only more efficient, but are cheaper in the long run. More critical experiments are needed in the various countries to find the best inorganic fertilizer, in particular to ascertain whether potassium and nitrogen are necessary.
