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Cultured Aquatic Species - Grass Carp

Information on the culture of the grass carp (Ctenopharyngodon idellus Valenciennes) from the FAO Cultured Aquatic Species Information Programme.

Identity 

Ctenopharyngodon idellus Valenciennes, 1844 [Cyprinidae]

FAO Names: En - Grass carp(=White amur), Fr - Carpe herbivore(=chinoise), Es - Carpa china

View SIDP Species fact sheet



Biological features

Body elongated and cylindrical, round abdomen, compressed at the rear; standard length is 3.6-4.3 times of body height and 3.8-4.4 times of head length; length of caudal peduncle is larger than the width; head medium; terminal mouth and arch-shaped; upper jaw extends slightly over lower jaw, its rear can reach below eye; snout width is 1.8 times of the length, snout length is about the nasal distance; no palpus; gill rakes short and sparse (15-19); two rows of pharyngeal teeth on each side, laterally compressed, formula 2.5-4.2, inner row stronger, grooves on the lateral surface; scales large and cycloid; extreme 39-46 scales in lateral line, lateral line extends to caudal peduncle. Anus close to anal fin; Dorsal fin ray: 3,7; pectoral fin ray: 1,16; ventral fin ray: 1,8; anal fin ray: 3,8; caudal fin with around 24 rays; body color: greenish yellow laterally, dorsal portion dark brown; greyish white in abdomen.

Profile

Historical background

Grass carp culture began in the areas along the Yangtze and Pearl Rivers in the southern part of China. Compared to common carp, the culture of grass carp started much later. According to historical records, the culture of grass carp was closely related to the will of the current governor.

In the Tang Dynasty (618-904 A.D.), the family name of the emperor happened to be pronounced the same in Chinese as common carp, the only fish cultured then. The royal family prohibited common carp to be sold and killed by the people. Therefore, grass carp was chosen by the farmers as a substitute for aquaculture together with silver carp, bighead and black carp; this was because the seed of these fish were easily available in the areas along the Yangtze River and the Pearl River.

The culture of grass carp remained relatively small in scale due to the dependence on the natural supply of seed. Success in induced breeding technology significantly promoted its culture. The fish has been introduced to more than 40 other countries; sometimes it is referred to as the white amur.

About 10 000 tonnes/yr in 1950, the global production of farmed grass carp had reached over 100 000 tonnes/yr by 1972, exceeded 1 million tonnes/yr by 1990, and has been above 3 million tonnes/yr since 1999. China is by far the major producer (3 419 593 tonnes in 2002, 95.7 per cent of the global total).

Main producer countries

In 2006, many countries reported cultured production of grass carp to FAO but only some of them (Bangladesh, China, Taiwan Province of China, Islamic Republic of Iran, the Lao People's Democratic Republic, Myanmar and Russian Federation) reported a production greater than 1 000 tonnes.


Main producer countries of Ctenopharyngodon idellus (FAO Fishery Statistics, 2006)

Habitat and biology

Grass carp is a native Chinese freshwater fish with a broad distribution from the catchment area of the Pearl River in southern China to that of the Heilongjiang River in northern China. It has been introduced to about 40 other countries and there have been limited reports about the natural populations occurring in those areas; for instance, a natural population exists in the Red River in Vietnam.

It inhabits lakes, rivers and reservoirs. It is a basically herbivorous fish that naturally feeds on certain aquatic weeds. However, the fry/larvae feed on zooplankton. Under culture conditions, grass carp can well accept artificial feed such as the by-products from grain processing, vegetable oil extraction meals, and pelleted feeds, in addition to aquatic weeds and terrestrial grasses. Grass carp normally dwell in mid-lower layer of the water column. Comparatively, it prefers clear water and can move swiftly.

It is a semi-migratory fish; the mature broodstock migrate to the upper reaches of major rivers to propagate. Flowing water and changes in water level are essential environmental stimuli for natural spawning. The fish can reach sexual maturity under culture conditions, but cannot spawn naturally. Hormone injection and environmental stimuli, such as flowing water are necessary for induced spawning in tanks. Gras carp grow rapidly and reach a maximum weight of 35 kg in the wild.

Production

Production cycle



Production cycle of Ctenopharyngodon idellus

Production systems

Various production systems are currently used for the culture of grass carp the major ones include semi-intensive and intensive culture ponds, and pens and cages in open waters.

Seed supply

At present artificial propagation is the major supply of seed for the culture of grass carp, although natural seeds are still available in some rivers of China. Seed collected from the wild is mainly used for maintaining the genetic quality of the broodstock. Broodstocks used for artificial propagation are usually raised in captivity from seeds from the wild or from breeding stations where good natural stocks are maintained.

Hatchery production

Well-matured breeders are released into the spawning tank (round cement tank with diameter of 6-10 m and water depth of around 2 m) after being injected with inducing hormone (usually LRH-A). Water circulation is maintained throughout the spawning period.

Eggs are transferred to hatching raceways or jars, either manually or by gravity. Hatching raceways (which are round or ellipse-shaped structures) are commonly used for large-scale production. The width of the raceways is normally 0.8 m and the depth is 0.8-1.0 m. The inlets are mounted on the bottom of the raceways with openings in the same direction and at an angle of around 15° to the bottom, to promote water circulation. Screens are mounted on the inner wall for discharging water during the operation. Water can be totally drained out through the outlet on the bottom. Current flow is maintained during the hatching period to keep the eggs and larvae suspended in the water column.

In India, dry or wet stripping methods are used for the seed production of grass carp. Pituitary extract or synthetic agents such as ovaprim are used for induction (John Stephen Kumar, pers. comm. 2004).

Nursery

Earthen ponds (usually 0.1-0.2 ha and 1.5-2.0 m deep) are used for the nursing of grass carp. Ponds are chemically cleared, normally with quicklime, to eliminate all harmful organisms after totally drying. The usual dose is 900-1 125 kg/ha.

Organic fertiliser, animal manure and/or plant wastes (‘green manure‘) is commonly applied to increase the natural biomass of algae and zooplankton 5-10 days before the stocking, according to the water temperature. The quantity of organic fertiliser used is usually 3 000 kg/ha for animal manure or 4500 kg/ha for green manure. Green and animal manures can be used simultaneously but the quantity of each should be reduced accordingly.

Monoculture is practiced in the nursery stage, with a stocking density normally ranging between 1.2-1.5 million/ha, depending on the length of rearing and targeted size. The nursery operation usually takes 2-3 weeks in China.

Organic fertilisation is carried out at frequencies and rates sufficient to maintain high pond fertility and therefore a good supply of natural food organisms (especially zooplankton) for the fish. The quantity ranges from 1 500-3 000 kg/ha once every 4-5 days for animal manure or green manure, depending on existing water fertility.

Soybean milk can also be used as both direct feed and fertiliser to replace organic fertiliser in the nursery stage. The normal quantity is 3-5 kg (dry soybean)/100 000 fish daily. This usually means production costs are high. A paste-form of soybean cake or other by-products from grain processing is applied from the 5th day after stocking, usually at a rate of 1.5-2.5 kg/100 000 fish daily.

A paste of water peanut, water lettuce and water hyacinth can also be used to replace the above-mentioned feed and fertilisers at the rate of 25-40 kg/100 000 fish daily. 0.5 per cent of table salt needs to be added to the paste of water peanut to remove its saponin toxicity. Normal survival rates in nursery ponds are 70-80 per cent, although it may reach over 90 per cent under good management.

The fish usually reach the size of about 30 mm in length after 2-3 weeks of rearing. These are called summer-fingerlings in China and are ready for the fingerling rearing stage. Conditioning, through careful netting and holding the fish at high density for a while (several hours) is required before the transfer of summer-fingerlings to the fingerling pond. This practice is designed to fish tolerance to stress before they are transported.

Rearing fingerlings

Summer-fingerlings are not suitable for direct stocking in grow-out ponds; they need to be reared to the fingerling stage (13-15 cm in length or larger) first. The technique for fingerling rearing is rather different to the nursery operation, especially when grass carp are stocked as the major species. The major differences include the following:

  • Relatively larger (0.2-0.3 ha) and deeper earthen ponds are used for fingerling rearing.
  • Contrary to the nursery stage, polyculture is usually adopted for the production of grass carp fingerlings (monoculture at this stage is quite rare). Grass carp can be polycultured with other carp species except black carp (Mylopharyngodon piceus).
  • The stocking density is 120 000-150 000/ha when it is the major species in the pond or 30 000/ha when it is the secondary species.
  • Feeding is vitally important throughout the fingerling rearing period. Grass carp are mainly fed with Wolffia arrhiza when it is between 30-70 mm in length. The initial feeding rate is 10-15 kg/10 000 fish daily and is gradually increased according to the demand of the fish. The feed is changed to duckweed (Lemna minor) when the fish is between 70-100 mm in length. After that, the fish can be fed with tender aquatic weeds and terrestrial grasses. In addition, commercial feeds (soybean cake, rapeseed cake, wheat bran, rice bran, etc.) are also fed at a daily rate of 1.5-2.5 kg/10 000 fish.
  • Fingerling rearing normally takes 4-6 months for above mentioned size and stocking density in China. The period can be considerably shortened in warmer climates or if lower stocking densities are used.
  • The normal survival rate through the whole fingerling rearing period should be above 95 per cent.

It is difficult to culture grass carp from the yearling size (13-15 cm) to marketable size (>1 500 g) within one year in most parts of China; it is therefore common practice to rear yearlings to 2 year old fingerlings for grow-out stocking. The stocking density is much reduced, compared to the rearing of yearlings. The feeding regime is similar but the rate is much higher. By the end of this period, the fish have usually reached about 250 g. This practice is not necessary in tropical and subtropical areas, where yearlings of grass carp can reach marketable size within one year, due to high temperatures.

In Vietnam, the rearing of grass carp before the grow-out stage is divided into two periods. Fry are first raised to 4-5 cm, with a stocking density in the earthen nursery pond of 200-250 fry/m². The rearing period is normally 1.5-2 months. Then the fish are further raised for about 2 months to a size of 12-15 cm at a much lower density. The fish is mainly fed with soybean powder, rice bran, maize powder and aquatic plants (Azolla sp.) after reaching 3 cm in body length.

The nursery rearing of grass carp in India is carried out in intensively fertilised ponds, adequately enriched with zooplankton and unicellular algae. Generally the survival of fry is about 70-80 per cent in well-managed nursery ponds. In addition to the natural feeds developed, supplementary feeding with powdered groundnut oilcake and rice polishings or bran is also practiced (John Stephen Kumar, pers. comm. 2004).

Ongrowing techniques

The most commonly adopted ongrowing techniques for grass carp include polyculture in ponds and pen and cage culture in lakes and reservoirs.

Semi-intensive to intensive polyculture in ponds in China

For polyculture in ponds or pens, grass carp can be stocked either as the major species or a secondary species together with other carp species. The total stocking density is 750-3 000 fish/ha with a stocking size of 125-250 g. Aquatic weeds and terrestrial grasses form the major feed for grass carp in grow-out culture. Feeding commercial feeds such as pellets and by-products from vegetable oil extraction and grain processing are becoming more popular as a means of replacing aquatic weeds and grasses to save labour costs in pond culture. The yield of grass carp is usually 1 000-3 000 kg/ha, which accounts for 15-40 per cent of the total production.

Intensive culture in cages in China

In intensive culture systems in cages, grass carp are usually stocked as major species. Cages are usually about 60 m², with a depth of 2-2.5 m. 250-500 g fish are stocked at 10-20/m³, depending on the targeted production. In addition, 30-50/m³ Wuchang fish (bluntnose black bream, Megalobrama amblycephala), are also stocked at a size of 80-125 g. Silver and bighead carp are also stocked at 1 per cent of the total, as 'cage cleaners'.

The fish are fed with aquatic weeds/terrestrial grasses and pelleted or other commercial feeds. The culture period is usually 8-10 months and the yield is normally 30-50 kg/m³. Grass carp usually account for 60-70 per cent of the total production. Cage culture of grass carp through the use of commercial feeds involves relatively high production costs.

Feeding efficiency is not always as high in cage culture as in pond culture so, where terrestrial grass and aquatic weeds are locally abundant, collecting them and applying them in cage culture usually requires less labour input as the transportation is limited.

Grow-out systems in other countries

The grow-out of grass carp is mainly conducted in earthen ponds and cages in Vietnam. Polyculture with other species (e.g. silver carp, common carp, rohu and mrigal etc.) is common. Grass carp may be stocked as either major or secondary species. Grass carp usually account for 60 per cent of the total stocking density of 1.5-3 fish/m² (dependent on the level of intensity) in ponds and the fingerling size is 5-6 cm (mountainous areas) and 12-15 cm (lowlands).

The stocking rate in cage culture is 20-30 fish/m³ but much larger fingerlings are used (normally 50-100 g). Grass carp are usually fed with terrestrial grasses, cassava leaves, banana stems and maize leaves in grow-out culture. Grass carp production usually accounts for 60 per cent of total production (7-10 tonnes/ha) in ponds. The marketing size for grass carp is 1-1.5 kg and 1.5-2.5 kg in ponds and cages respectively.

In India, grass carp are cultured as an important species in pond-based composite systems consisting mainly of Indian major carps and Chinese carps. The grass carp stocking density depends mainly on the availability of aquatic weeds and terrestrial grasses but is usually 5-20 per cent of the total. Aquatic weeds (Hydrilla, Vallisneria, Wolffia) and terrestrial grasses such as Napier grass and other hybrid grasses are the major feeds in grass carp farming. Normally, grass carp reach 0.5-1.5 kg in 8-10 months (John Stephen Kumar, pers. comm. 2004). The total production from such systems can reach 8-10 tonnes/ha/yr.

Feed supply

Grass carp can be reared with commercial feeds or natural food, such as aquatic weeds and grasses. They prefer relatively low fertility. Production is mainly limited by water quality. The commercial feeds used for grass carp are relatively low in protein (28-30 per cent) and their raw materials include soybean cake/dregs, rapeseed cake and wheat bran etc. Aquatic weeds can be collected from natural water bodies. Terrestrial grasses can be grown on the pond dyke with organic manure.

Harvesting techniques

Both selective and total harvesting are practiced for grass carp. Selective harvesting is usually conducted in the early morning (because temperatures are relatively low and for morning sales) during late summer and autumn. Individuals of marketable size are selected after netting (a single netting for each harvest). Total harvesting is carried out at the end of the culture period. Several nettings are usually carried out before total drain-down of the pond. All the fish are harvested at the end of the year, either for marketing or for restocking (individuals below marketable size) for the next production cycle.

Handling and processing

Grass carp is normally sold live or fresh. A small quantity of the production is processed by ready-to-eat food stores; in this case the most commonly used processing method is deep frying.

Production costs

The production cost of grass carp vary according to the culture practice used but are normally about USD 0.50/kg of fish produced. Feed costs comprise the largest portion of production costs.

Diseases and control measures

Farmed grass carp are rather susceptible to various diseases. Major diseases and methods of control are listed in the table below.

Full Story


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