Fisheries :: Integrated Farming System
The principle of integrated fish farming involves farming of fish along with livestock or/and agricultural crops. This type of farming offers great efficiency in resource utilization, as waste or byproduct from one system is effectively recycled. It also enables effective utilization of available farming space for maximizing production. The rising cost of protein-rich fish food and chemical fertilizers as well as the general concern for energy conservation have created awareness in the utilization of rice and other crop fields and livestock wastes for fish culture. Fish culture in combination with agriculture or livestock is a unique and lucrative venture and provides a higher farm income, makes available a cheap source of protein for the rural population, increases productivity on small land-holdings and increases the supply of feeds for the farm livestock. The scope of integrated farming is considerably wide. Ducks and geese are raised in pond, and pond-dykes are used for horticultural and agricultural crop products and animal rearing. The system provides meat, milk, eggs, fruits, vegetables, mushroom, fodder and grains, in addition to fish. Hence this system provides better production, provides more employment, and improves socio-economic status of farmers and betterment of rural economy.
Integrated fish farming can be broadly classified into two, namely: Agriculture-fish and Livestock-fish systems. Agri-based systems include rice-fish integration, horticulture-fish system, mushroom-fish system, seri-fish system. Livestock-fish system includes cattle-fish system, pig-fish system, poultry-fish system, duck-fish system, goat-fish system, rabbit-fish system.
Agri-based systems include rice-fish integration, horticulture-fish system, mushroom-fish system, seri-fish system. In this system, fish culture is integrated with agricultural crops such as rice, banana and coconut, thereby producing fish and agricultural crops under one interlinked system.
In India, though six million hectares are under rice cultivation, only 0.03 per cent of this is now used for rice-fish culture. This type of fish culture has several advantages such as (a) economical utilisation of land, (b) little extra labour, (c) savings on labour cost towards weeding and supplemental feeding, (d) enhanced rice yield, and (e) additional income and diversified harvest such as fish and rice from water, and onion, bean, and sweet potato through cultivation on bunds. Considering these, it is imperative to expand fish culture in the rice fields of our country.
For the culture of fish in combination with rice, varieties such as Panidhan, Tulsi, CR260 77, ADT 6, ADT 7, Rajarajan and Pattambi 15 and 16 are suitable. These varieties not only possess strong root systems but also are also capable of withstanding flooded conditions. Further, they have a life span of 180 days and fish culture is possible for about four to five months after their transplantation. Harvesting is done when fish attain marketable size.
Fish culture in rice fields may be attempted in two ways, viz. simultaneous culture and rotation culture. In the former, rice and fish are cultivated together and in the latter; fish and rice are cultivated alternately.
For simultaneous culture, rice fields of 0.1 ha area may be economical. Normally four rice plots of 250 m2 (25 x 10 m) each may be formed in such an area. In each plot, a ditch of 0.75 m width and 0.5 m depth is dug. The dikes enclosing the rice plots may be 0.3 m high and 0.3 m wide and are strengthened by embedding straw. The ditches have connections with the main supply or drain canal, on either side of which, the rice plots are located, through inlet-outlet structures of the dikes. The depth and width of the supply or drain canal may be slightly smaller than that of the ditches. Suitable bamboo pipes and screens are placed in the inlet and outlet structures to avoid the entry of predatory fish and the escape of fish under culture. The ditches serve not only as a refuge when the fish are not foraging among rice plants, but also serve as capture channels in which the fish collect when water level goes down. The water depth of the rice plot may vary from 5 to 25 cm depending on the type of rice and size and species of fish to be cultured.
The fish species which could be cultured in rice fields must be capable of tolerating shallow water (15 cm), high temperatures (up to 35ºC), low dissolved oxygen and high turbidity. Species such as Catla catla, Labeo rohita, Cirrhina mrigala, Cyprinus carpio, Chanos chanos, Oreochromis mossambicus, Anabas testudineus, Mugil spp., Clarias batrachus, C. macrocephalus, Lates calcarifer, Channa striatus and C. marulius have been widely cultured in rice fields.
Simultaneous Culture Of Fresh-Water Prawn And Rice
Semi-intensive culture of Macrobrachium rosenbergii could be undertaken in rice fields. Unlike for fish-rice culture, bunds for fish-prawn culture are raised so as to enclose 12 cm of water for four months, the period of rice culture. Further, inlets and outlets should be provided with extended screen, say, 0.3 m above water surface to prevent climbing and escape of prawns. One or two small sump pits (1 x 2 x 0.5 m) should also be constructed near the outlet for trapping prawns when water is drained at the time of harvesting. The stocking of juvenile prawns (2-3 cm size) at the rate of 1,000/ha may be done after the rice seedlings are well rooted. No supplementary feeding of prawns is required in this system.
The simultaneous culture has the following advantages:
Limitations in simultaneous culture: The simultaneous fish-rice culture may have some limitations, like (a) use of agrochemicals is often not feasible, (b) maintaining high water level may not be always possible, considering the size and growth of fish, (c) fish like grass carp may feed on rice seedlings, and (d) fish like common carp and tilapia may uproot the rice seedlings. However, these constraints may be overcome through judicious management.
Five days after transplanatation of rice, fish fry (1 cm) are stocked at the rate of 5,000/ha or fingerlings (8-10 cm) at the rate of 2,000/ha. The stocking density can, however, be doubled if supplemental feed is given daily, particularly if plankton is found depleted after 10 days of stocking fish. The plankton production in rice fields could, however, be increased if some amount of fertiliser more than what is required for rice fields is added. To control the menace of insects, the insecticide Furadon (Carbofuran) may be used at the rate of 1 kg/ha. The insecticide is mixed with basal fertilisers and applied once during the final harrowing. It may be stated that fish grown in insecticide-applied rice fields are safe for human consumption.
After a period of 10 weeks (if stocked with fry) or six weeks (if stocked with fingerlings), the rice fields are slowly drained off and the fish are harvested. The harvesting of fish may be done about a week before the harvest of rice. The growth rate of fish is also moderate in rice fields as the production of plankton, the fish food organisms, is rich. Individual growth of 60 g and a per hectare yield of 500 kg have been reported under the simultaneous culture practice.
Rotational culture of rice and fish
Through this practice, fish and rice are cultivated alternately. The rice field is converted into a temporary fishpond after the harvest. This practice is favoured over the simultaneous culture practice as it permits the use of insecticides and herbicides for rice production. Further, a greater water depth (up to 60 cm) could be maintained throughout the fish culture period.
One or two weeks after rice harvest, the field is prepared for fish culture. C. carpio is found suitable for this practice. The stocking densities of fry (2-3 cm) or fingerlings (5-8 cm) for this pracitce could be 20,000/ha and 6,000/ha, respectively. The fry are harvested after 10 weeks, while the fingerlings after six weeks. The average growth of the individual fish under this system has been reported to be about 100 g and a fish yield of about 2,000 kg/ha is possible. Further, it has also been reported that fish yield could exceed the income from rice in the rotational culture.
Paddy Cum Fish Culture
Coastal saline soil extends from the main sea coast to a few or even 50 km at places interior to the main land. The ground water table under these soils is generally present at a shallow depth and contains high amount of soluble salts. These salts accumulate on the surface of the soil due to capillary rise of saline groundwater during dry periods of the year rendering the soil highly saline. Almost the entire area of the rain fed coastal saline soil is mono cropped in nature. The major agricultural crop of kharif is rice, grown during monsoon period when soil salinity is low. During the rest of the year, the land usually remains fallow due to high salt content of the soil.
The kharif paddy varieties widely used in such areas are Mahsuri, Sadamota, Kalomota, Talmugur, Damodar, Dasal, Getu, Nona-patnai, Jaya, Ratna, Pankaj, Patnai-23, Luni, Cuttackdhandi, Pokkali, Vytilla, Bilikagga, CSR-4, CSR-6, Matla, Hamilton, Palman 579, BKN, RP-6, FR-46B, Arya, etc. Paddy cum brackish water fish/ shrimp culture aims at utilizing the summer fallow period of the coastal saline soil through a short-term brackish water aquaculture without affecting the subsequent kharif paddy crop. This type of activity provides the farmers with a substantial subsidiary income during the fallow season.
In West Bengal, where the salinity is either low or lowered by fresh water discharge diluting the tidal water, the cultivation of fish is undertaken in paddy fields. In pokkali fields of Kerala, summer fallow months are utilized for brackish water aquaculture. The production of fish in such culture varies from 300 to 1000 kg/ha. The brackish water shrimp culture is introduced in a big way in such areas as the remuneration is very high. The species commonly cultured are Penaeus monodon, Penaeus indicus, Metapenaeus dobsonii and Metapenaeus monoceros.
The coastal area is mostly low lying, the elevation varying usually between sea level and 8 m above the MSL. Fields having elevation between low and high tide levels are desirable for water exchange during brackish water aquaculture and also for frequent draining of monsoon water during desalination process. The sluice in the embankment is essential for regulating the flow of tidal and drainage waters. The area having more than 1 m tidal amplitude is considered suitable for paddy cum shrimp culture.
Medium textured soils like silty clay or silty clay loam are most suitable for paddy cum fish/ shrimp culture.
Heavy monsoon precipitation for the site is essential for desalination of the soil after brackish water aquaculture. Intake of brackish water must be suspended before the onset of monsoon. The cultured species is harvested and then the land is exposed to monsoon precipitation for the purpose of desalination.
The paddy plots should be renovated suitably for the purpose of paddy cum brackish water aquaculture. Construction of an earthen dyke surrounding the paddy plot is essential for retaining water and also for holding the fish and shrimp during aquaculture. The height of the dyke is required to be maintained between 50 and 100 cm depending upon the topography of the plot and tidal amplitude at the site. A perimeter canal is necessary on the inner periphery of the plot. For a one ha paddy plot, the width and depth of the canal may be about 2 m and 1 m respectively. The earth removed from excavating the canal may be utilized for constructing or strengthening the dyke. In addition to the perimeter canal, two cross trenches of about 1 m width should also be constructed at both the directions. The bottom of the trenches should be above the perimeter canal so that during the course of desalination, entire water can be easily removed to the canal. The area covered by the perimeter canal and the trenches will be about 12% of the total land area.
Water supply and drainage
The entry of tidal water during the culture is made through feeder canal and the flow of water into the field is regulated by a sluice gate fitted with wooden shutters and placed at about 30 cm height from the main plot. During high tide, water is taken into the plot after sieving through velon nets and split bamboo mats to prevent entry of any kind of fish/ shrimp and other undesirable species, especially carnivores. Another sluice is used for draining out water from the culture plot to the feeder canal at low tide periods for water exchange, desalination and drainage of excess water. On the entry and exit mouths of the slice gate, wooden shutters are provided to regulate the movement of water.
The plots are prepared in two phases, once for brackish water aquaculture and again for paddy cultivation. For aquaculture crop, the plot is sun dried after the kharif harvest. If necessary, to rectify acidic soils, lime is applied depending on requirement of the soil. Usually no inorganic fertilization is done. However, urea may be used in extreme cases of nitrogen deficiency of soils @ 60 kg N/ha. Some shade zones are provided over the perimeter canal with twigs, hay, palm leaves etc., so that during summer the shrimp can take shelter and also hide themselves from predation.
The paddy field is made ready for stocking and Penaeus monodon or Penaeus indicus are stocked @ 3 nos/sq.m.
Although natural food items have good conversion values but they are difficult to procure in large quantities and maintain a continuous supply. Hence only supplementary feed is given
Complete harvesting is done by draining the pond water through a bag net and hand picking. The average culture period in paddy fields is around 100-120 days during which time the shrimps will grow to 35 gm size. Harvested shrimps can be kept between layers of crushed ice before transporting the consignment to market.
Fish Culture In 'Pokkali' Fields
In Kerala, fish and prawn are cultured on rotational basis in Pokkali rice fields. These fields under the influence of Vembanad backwaters, which are in, turn controlled by tides. As these fields are flooded during southwest monsoon (June-Septemeber) rice is cultivated. Fish and prawns are cultured during other periods. Immediately after the harvest of rice, the fields are leased out for the culture of fish and prawns. The young of fish and prawns enter the fields from nearshore waters along with high tides. Suitable management cultures these young until harvest in May. These fields are rich in plankton owing to the decaying of paddy stumps. A prawn yield of 500-1,200 kg/ha has been obtained from Pokkali fields. After the prawn harvest, the water is drained off. Subsequently, the saline nature of rice fields is nullified because of the monsoon rains and the fields are again made fit for rice culture.
The top, inner and outer dykes of ponds as well as adjoining areas can be best utilized for horticulture crops. Pond water is used for irrigation and silt, which is a high-quality manure is used for crops, vegetables and fruit bearing plants. The success of the system depends on the selection of plants. They should be of dwarf type, less shady, evergreen, seasonal and highly remunerative. Dwarf variety fruit bearing plants like mango, banana, papaya, coconut and lime are suitable, while pineapple, ginger, turmeric, chilli are grown as intercrops. Plantation of flower bearing plants like tuberose, rose, jasmine, gladiolus, marigold and chrysanthemum provide additional income to farmers.
Ideal management involves utilization of middle portion of the dyke. Residues of vegetables cultivated could be recycled into fishponds, particularly when stocked with fishes like grass carp. Grass carps can be stocked @ 1000/ha and addition of common carps are beneficial for utilizing feacal debris. In mixed culture of grass carps along with rohu, catla and mrigal, in 50: 15: 20: 15 ratio at a density of 5000 fish/ha. Similarly when banana or coconut is cultivated in rows in wetlands, the ditches made between such rows act as supply or drainage canals. These canals serve as fish culture systems owing to their round-the-clock supply of water and rich insect populations. Larvivorous air-breathing fish species such as snakeheads C. marulius and C. striatus and tilapia, O. mossambicus are ideal species for culturing in this system. This integrated system fetched 20-25% higher return compared to aquaculture alone.
Cultivation of edible mushroom in India is quite recent. Three types of mushrooms being commercially cultivated in India are Agaricus bisporus, Voloriella spp. and Pleurotus spp., commonly known as European button, paddy straw and oyster mushroom. Mushroom cultivation requires high degree of humidity and therefore its cultivation along with aquaculture tremendous scope. Method of cultivation involves use of dried paddy-straw chopped into 1.2 cm bits, soaked in water overnight. Excess water is drained off. Horsegram powder (8 g/kg straw) and spawn (30 g/kg straw) is added and mixed with wet straw in alternating layers. Perforated polythene bags are filled with substrate and kept in room at 21o-35oC with required light and ventilation. The mycelial growth occurs within 11-14 days. Polythene bags are cut open at this stage, water is sprayed twice a day and in a few days mushroom crop becomes ready for harvest. The paddy-straw after mushroom cultivation is utilized for cattle feeding.
In this integration, mulberry is the producer; silkworm is the first consumer while fish is the secondary consumer, ingesting silkworm faeces directly. Inorganic nutrient in the silkworm faeces are utilized by phytoplankton, and filter-feeding fish in turn consumes heterotrophic bacteria. The optimum range of temperature and humidity is 15-32oC and 50-90% respectively. The seri-fish system provides linkages between mulberry and pond sub-system. Harvested mulberry leaves are fed to silkworm and the waste material obtained from silkworm rearing enters fish-pond as a mixture of mulberry leaves and silkworm excrement. Mulberry dykes yield leaves at 30 tonnes/ha/year, when fed to silkworm 16-20 tonnes of waste is produced. In 1 ha mulberry-pond system, 50% of area is kept for dyke and remaining is kept as water area. During winter, vegetables are inter-planted with mulberry. A production of 30 tonnes of mulberry-leaves/ha, 3.75 tonnes of vegetables/ha can be attained.
Livestock-fish system includes cattle-fish system, pig-fish system, poultry-fish system, duck-fish system, goat-fish system, rabbit-fish system. In this practice, excreta of ducks, chicks, pigs and cattle are either recycled for use by fish or serve as direct food for fish. Hence, the expenditure towards chemical fertilisers and supplementary feeds for fish culture is not only curtailed to the barest minimum but also there is economy of space. Integration of fish culture and livestock farming is in vogue in many countries and the income realised has been found to be more than that of exclusive fish farming in ponds.
The main potential linkages between livestock and fish production concern use of nutrients, particularly reuse of livestock manures for fish production. The term nutrients mainly refers to elements such as nitrogen (N) and phosphorous (P) which function as fertilizers to stimulate natural food webs rather than conventional livestock nutrition usage such as feed ingredients, although solid slaughterhouse wastes fed to carnivorous fish fall into the latter category.Both production and processing of livestock generate by-products that can be used for aquaculture. Direct use of livestock production wastes is the most widespread and conventionally recognized type of integrated farming. Production wastes include manure, urine and spilled feed; and they may be used as fresh inputs or be processed in some way before use.
Use of wastes in static water fishponds imposes limitations in terms of both species and intensity of culture. Stimulation of natural food webs in the pond by organic wastes can support relatively low densities of herbivorous and omnivorous fish but not a large biomass of carnivorous fish. These biological processes are also temperature dependent. The optimal temperature range is between 25-32°C although waste-fed aquaculture in sub-tropical and temperate zones where temperatures rise seasonally has also been successful. Processing wastes through organisms such as earthworms and insect larvae that feed on them and concentrate nutrients to produce ‘live feeds’ is an alternative approach to raising fish needing high levels of dietary animal protein. Livestock processing can also provide a wide variety of wastes that vary from dilute washing water to high value meat and bloodmeal that can be used as high value fish feeds or feed ingredients. If enough of these types of feeds are available, high density and intensive production of carnivorous fish species can be supported. Aquaculture may also provide inputs and other benefits to livestock production. A variety of aquatic plants e.g. duckweeds and the aquatic fern Azolla have proven potential as livestock feeds; and invertebrates such as snails and crustaceans can be used for poultry feeds.
Based on the type of livestock used for integration there are many combinations in livestock-fish systems. The important ones are discussed below.
Fish farming using cow manure is one of the common practice all-over the world. Countries like Hong Kong, Taiwan and Philippines have undertaken the integrated fish farming on a commercial scale and obtained considerable fish yields. Cowsheds are constructed in the vicinity of fishponds and the slurry from the biogas plants may be discharged into fishponds. A healthy cow excretes over 4,000-5,000 kg dung, 3,500-4,000 litre urine on an annual basis. Cow manure particles sink slower (6 cm/min) than any other livestock. This provides sufficient time for fish to consume edible portions available in dung. Manuring with cowdung, which is rich in nutrients result in increase of natural food organism-detritus and bacteria in fishpond. A unit of 5-6 cows can provide adequate manure for 1 ha of pond. In addition to 9,000 kg of milk, about 3,000-4,000 kg fish/ha/year can also be harvested with such integration.
Cowshed should be built close to fishpond to simplify handling of cow manure. Cow requires about 7,000-8,000 kg of green grass annually. Grass carp utilizes the leftover grasses, which are about 2,500 kg. Fish also utilizes the fine feed wasted by cows, which consist of grains. In place of raw cowdung, biogas slurry could be used with equally good production. 20,000-30,000 kg of biogas slurry is recycled in 1 ha water area to get over 4000 kg of fish without feed or any fertilizer application.
This system of integration is very common in China, Taiwan, Vietnam, Thailand, Malaysia and Hungary. Pigs are fed largely on kitchen waste, aquatic plants and crop wastes. The waste produced by 30-35 pigs is equivalent to 1 tonne of ammonium sulphate. Exotic breeds such have White Yorkshire, Landrace and Hampshire are reared in pig-sty near the fish pond. A floor space of 3-4 m2 is provided and boars, sows and finish stocks are housed separately. Maize, groundnut, wheat-bran, fishmeal, mineral mixes are provided as concentrate feed-mixture.
Depending on the size of the fishponds and their manure requirements, such a system can either be built on the bund dividing two fishponds or on the dry-side of the bund. Pigsties, however, may also be constructed in a nearby place where the urine and dung of pigs are first allowed to the oxidation tanks (digestion chambers) of biogas plants for the production of methane for household use. The liquid manure (slurry) is then discharged into the fishponds through small ditches running through pond bunds. Alternately, the pig manure may be heaped in localised places of fishponds or may be applied in fishponds by dissolving in water.
Pigdung contains more than 70 per cent digestible feed for fish. The undigested solids present in the pigdung also serve as direct food source to tilapia and common carp. A density of 60-100 pigs has been found to be enough to fertilise a fish pond of one hectare area. The optimum dose of pig manure per hectare has been estimated as five tonnes for a culture period of one year. Such a quantity may be obtained from 50 well-fed pigs. If the manure is to be applied in a dry form, a dosage of 400 kg/ha/day for 12 times in a year will be required. Fish like grass carp, silver carp and common carp (1:2:1) are suitable for integration with pigs.
Pigs attain slaughter maturity size (60-70 kg) within 6 months and give 6-12 piglets in every litter. Their age at first maturity ranges from 6-8 months. Fish attains marketable size in a year. Keeping in view the size attained, prevailing market rate, demand of fish, partial harvesting of table-sized fish is done. Final harvesting is done after 12 months of rearing. It is seen that a fish production of 3,000 kg/ha could be achieved under a stocking density of 5,000 fish fingerlings/ha in a culture period of six months. In India, through pigfish culture, the fish yield was doubled compared to that of polyculture with intensive feeding.
The droppings of chicks rich in nitrogen and phosphorus would fertilise fishponds. Poultry housing, when constructed above the water level using bamboo poles would fertilise fishponds directly. This system utilizes poultry droppings for fish culture. Production levels of 4500-5000 kg/fish/ha could be obtained by recycling pond manure into fishponds. Broiler production provides good and immediate returns to farmers. Procurement of quality chicks, housing, brooding, feeding and disease management are important for this type of system. In fish poultry integration, birds housed under intensive system are considered best. Birds are kept in confinement with no access to outside. Deep litter is well suited for this type of farming. About 6-8 cm thick layer prepared from chopped straw, dry leaves, saw dust or groundnut shell is sufficient.
Rhode island or Leghorn birds are preferred in poultry-fish system for their better growth and egg laying capacity. The number of chicks used for this system is about 2500/ha however; the stocking density of chicks may be increased in the event of increase in the stocking density of fish fingerlings. Egg-type birds are fed with starter 0-8 weeks, grower 8-20 weeks and brooder feed 20 weeks onwards, while broilers are fed 0-4 weeks with starter and 4-6 weeks with finisher feed. The deep poultry litter is applied to pond in daily doses at 30-35 kg/ha. One adult chicken produces about 25 kg of compost poultry-manure in a year; 1000 birds can provide sufficient manure for 1 ha water body.
Fertilization with poultry manure results in a production of 3000-4000 kg fish, 90,000-100,000 eggs and over 2,500 kg meat/ year. A fish production of 10 tonne/ha could be obtained by culturing tilapia, common carp and murrels with a stocking density of 20,000 fingerlings/ha and chick density of 4,000/ha. No chemical fertilisers or supplemental feeds have to be given at any stage. By stocking 5,000 giant fresh-water prawn, Macrobrachium rosenbergii and 1,500 silver carp in one-hectare area, one can harvest 600 kg of prawns and an equal amount of fish in a four-month culture period.
Duck-fish integration is the most common integration in China, Hungary, Germany, Poland, Russia and some parts of India. A fish-pond being a semi-closed biological system with several aquatic animals and plants, provide excellent disease-free environment for ducks. In return ducks consume juvenile frogs, tadpoles and dragonfly, thus making a safe environment for fish. Duck dropping goes directly in pond, which in turn provide essential nutrients to stimulate growth of natural food. This has two advantages, there is no loss of energy and fertilization is homogeneous. This integrated farming has been followed in West Bengal, Assam, Kerala, Tamil Nadu, Andhra Pradesh, Bihar, Orissa, Tripura and Karnataka. Most commonly used breed for this system in India is the ‘Indian runners’.
It is highly profitable as it greatly enhances the animal protein production in terms of fish and duck per unit area. Ducks are known as living manuring machines. The duck dropping contain 25 per cent organic and 20 per cent inorganic substances with a number of elements such as carbon, phosphorus, potassium, nitrogen, calcium, etc. Hence, it forms a very good source of fertiliser in fish ponds for the production of fish food organisms. Besides manuring, ducks eradicate the unwanted insects, snails and their larvae which may be the vectors of fish pathogenic organisms and water-borne disease-causing organisms infecting human beings. Further, ducks also help in releasing nutrients from the soil of ponds, particularly when they agitate the shore areas of the pond.
For duck-fish culture, ducks may be periodically allowed to range freely, or may be put in screened resting places above the water. Floating pens or sheds made of bamboo splits may also be suspended in the pond to allow uniform manuring. The ducks may be stocked in these sheds at the rate of 15 to 20/m2. It is better if the ducks are left in ponds only until they reach marketable size. Depending on the growth rate of ducks, they may be replaced once in two to three months. About 15-20 days old ducklings are generally selected. The number of ducks may be between 100 and 3,000/ha depending on the duration of fish culture and the manure requirements.
For culturing fish with ducks, it is advisable to release fish fingerlings of more than 10 cm size, otherwise the ducks may feed on the fingerlings. The stocking density of fingerlings also depends on the size of pond and number of ducks released in it. As the nitrogen-rich duck manure enhances both phyto- and zooplankton production, phytoplankton-feeding silver carp and zooplankton-feeding catla and common carp are ideal for duck-fish culture. The fish rearing period is generally kept as one year and under a stocking density of 20,000/ha, a fish production of 3,000-4,000 kg/ha/year has been obtained in duck-fish culture. In addition to this, eggs and duck-meat are also obtained in good quantity on an annual basis.
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