Culture of Chinese carp

Profile of Chinese carps

Silver carp, Hypophthalmichthys molitrix (Valenciennes, 1844) belongs to Cyprinidae family. Silver carp is a freshwater species and its natural distribution is in Asia. The species is found in river and backwater of larger rivers. Silver carp are planktivores, the gill rakers being the main means of filtration. Silver carp consume the diatoms, dinoflagellates, chrysophytes and xanthophytes. The larvae and juvenile consume the zooplankton, but after they reach about 1.5 cm size, they feed on phytoplankton only. Silver carp spawn when the water is high18 ºC and 30 ºC, with an optimum temperature of 22 - 28°C. The eggs of silver carp are non-adhesive. After spawning, the eggs begin to absorb water through the egg membrane and swell until its specific gravity is slightly greater than that of water, so they can stay at the bottom or float halfway in mid-water until the fry hatch.

Grass carp, Ctenopharyngodon idella (Valenciennes, 1844) also belongs to Cyprinidae family. It is a freshwater species, found around the world but its natural distribution is in Asia. Adults inhabit the lake, ponds, pools, and backwater of rivers. It prefers slow flow or standing water bodies along with vegetation. It can tolerate a broad range of temperature - 0 - 38 °C. The grass carp mainly feed on the aquatic plants and submerged grasses, but also consume the insects and other vertebrates. The grass carp is cultured to control the aquatic weeds.

Bighead carp, Hypophthalmichthys nobilis (Richardson, 1845), belongs to Cyprinidae family. It is a freshwater species, found around the world but its natural distribution is in Asia. Length at first maturity ranges between 55 – 70 cm with an average length of 65 cm. It is located in the rivers, lake, backwaters and flooded area with slow water current. Usually it breeds on the very turbid and deep water with temperature range of 22 - 30°C and high current of 1.1 – 1.9 m/s. It is a bottom feeding fish and mainly feed on zooplankton and also algae.

Broodstock selection and maintenance

Good quality broodstock is essential for seed production. Silver carp adults reach 4 – 6 yrs. old with a body weight of above 2.5 kg and is the ideal stage for induced spawning. Broodstock is stocked by weight, at 1500 – 2250 kg/ha, with a female: male ratio of about 1.0:1.5. Grass carp male mature one year earlier than the female fishes. Usually, maturity takes place between 3 – 8 yrs. It depends on the environmental condition where fishes are reared. The female of bighead carp of four years age and mud carp of three-years age are selected for artificial propagation.

The selected broodstock should be free from disease and injuries. The brood fishes are maintained in a single pond. It is desirable to keep them separately because the requirement is unique to each species. the brood fish of silver carp prefers small-fertilized pond with good growth of phytoplankton. The grass carp prefer clean water, so regular water renewal is necessary. The bighead requires water with a generous growth of zooplankton which can be produced through regular manuring.

The silver carp is fed with rice bran or soybean, twice a day at 3 – 5 percent of the body weight of the fish. 30 – 50 brood fishes of silver carp are stocked in 1000m². The feeding rate for grass is about 15 – 20 percent of the body weight, other foodstuffs is at 2.0 – 2.5 percent of body weight. About 20 – 30 brood fishes of grass carp are maintained in 1000 m². The stocking rate of bighead carp in a 1000 m² pond is about 20 – 25 fish and for mud carp it is 100 – 150 fish.

Inbreeding depression can be controlled by exchanging the brood fishes between the farmers and introduction of brood fishes from the natural water bodies. The selected brood fishes for spawning are largely based on their size and extent of maturation. The development stage of eggs is evaluated by removing a small amount of egg from the female by stripping method. The male is checked by the indicator that milt  oozes out easily when gently pressed on the abdomen towards the genital papilla. This indicates that they are ready for spawning.

Induced spawning

The brood fishes are introduced into the spawning tank after the hormonal treatment with a proportion of three males and two females. The inducing agents used are the pituitary of an extract of silver carp, common carp and bighead carp, the LRH (Luteinizing Release Hormone), LRH-A (Luteinizing Release Hormone-Analogue) and HCG (Human Chorionic Gonadotrophin).

For silver carp, the suggested dose of HCG is about 800 – 1000 IU/kg of brood fish. The silver carp and bighead carp respond well to the HCG, but the mud carp and grass carp appear to be less responsive to it. The LRH-A is more efficient on bighead carp, mud carp and grass carp rather than silver carp.

To facilitate the production and operation, it is to be ensured that fish spawn on daytime. If a single dose of injection method is adopted, it should be given at 16.00 hrs. If a double dose injection is selected, the first injection takes place between 14.00 – 16 hrs and second at about 24.00 hrs. The eggs are pelagic and non-adhesive; size ranges from 1.3 – 1.91 mm. The size of eggs increases after the fertilization. The hatch out depends on the water temperature, and usually, it takes 20 – 24 hrs at a temperature of 28 – 30 °C. The size of incubation and hatchling pools varies. Many of them have a capacity of 4.6 m³, with 2.9 m dia. and about 0.8 m depth. Such pools can stock 7 – 8 lakhs eggs/m³ with an average hatching rate of 80 percent. Suitable season, gonad maturity and environmental condition are the key factors for artificial propagation.

Fecundity of silver carp as a function of weight

Fecundity of grass carp as a function of weight

Fry production

The earthen pond used for nursery is of 0.1 – 0.2 ha with 1.5– 2.0 m depth. The 3 – 4 days old fry are stocked in the nursery pond. The stocking density directly affects the survival rate. When it is higher, survival will be low. It should not be too low also because it needs to cover the operating cost. The ideal stocking density is about 1.5 – 2.5 million/ha for silver carp and about 1.2 – 1.5 million/ha for grass carp. The expected survival rate is 70 – 80 percent. If its a well-managed pond, survival rate can get up to 90 percent. They are grown until 15 – 20 days when they measure 2.5 – 3.0 cm. The supplementary feed is given at daily two rations at 6 – 8 percent of the body weight. Normally, it is a mixture of rice bran, soybean and groundnut oil cake. The ponds are prepared in a similar way as is done for the Indian Major Carp culture ponds.

Fingerlings production

The fingerlings production pond is also prepared analogous to the nursery pond, but the insect control is not taken up. The cow dung (3 – 4 tons/ha) and single super phosphate (30 – 40kg/ ha) are added to the fingerling production pond before 10 days of stocking. After stocking, 500kg/ha cow dung and 10 kg/ha of single super phosphate are added twice in a month. The usage of cow dung is reduced to about one-third to half when poultry manure is applied. The fingerlings are required for larger sized pond (0.2 – 0.30 ha with a depth of 1.5 – 2.0 m. for grass carp) rather than fry.

The polyculture is practiced with silver, grass carp and Indian Major Carp. The fry is reared into fingerlings, which takes around 3 – 5 months. Silver carp can grow to about 8 – 12 cm of body length and the grass carp to about 13 – 15 cm. The Stocking density directly affects the growth of fish. Thereby, ideal stocking density is necessary for better production. The supplementary feed is provided daily two rations at the rate of 5 – 7 percent of body weight. For silver carp, supplemental feed is provided and is a mixture of rice bran or wheat bran with groundnut oil cake / mustard oil cake / cottonseed oil cake in the ratio of 1:1. The grass carp initially (when of size 3 – 7 cm) feed on Wolffia arrhizal at the rate of 10 – 15 kg for 10000 fishes. When they are of size 7 – 10 cm, they feed on Lemna minor and after that feed on the aquatic weeds and terrestrial grass. After attaining 10 cm size, the commercial feed (a mixture of soybean cake, rapeseed cake, wheat bran, rice bran) are also given at 1.5 – 2.5 kg per 10000 fishes.

Grow-out production

The grow-out pond is also prepared similar to the nursery and fingerlings pond. The fingerlings are considered ideal for stocking in medium sized ponds. The advanced fingerlings are the best stocking for temporary ponds, because they grow faster and can be marketed within 6 – 8 months. Advanced fingerlings are suggested for stocking in larger ponds and in open water where competitor and predator are present in good number. However, normally silver carp is cultured with composite fish culture along with Indian Major Carps and other Chinese carps.

Usually, the grass carp accounts for 60 percent of total stocking density in a pond of 1.5 – 3.0 fishes/ m². For cage culture, 20 – 30 fish/m³, size ranges from 50 – 100g. Food is the major factor, which determines the growth of fish. Natural food is not sufficient and hence supplementary feed is required. To meet the nutritional deficiency, extra ingredients such as soy flour, fish meal vitamins, mineral mixture, etc can also be included. Feeding is done preferably twice. The excess feed leads to deteriorating water quality and under feeding affects the growth of fish. The preferred feeding rate is 3 – 5 percent of the body of fish. The table size fish of silver carp is about 0.75 – 1.5 kg and the grass carp is 1.0 – 1.5 kg. In natural conditions, the grass carp grows about 5 kg in 3 yrs.

References

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