Detailed Explanation of Grass Carp Farming Methods and Technical Points

Grass carp, as a fish with relatively large sales volume on the market, also enjoys good market conditions, so there is no shortage of people interested in grass carp farming, since grass carp has great appreciation potential in the future market. Farming grass carp is relatively secure, and basically there will be no situation where grass carp cannot be sold.

How are grass carp farmed?

I. Pond conditions for grass carp

1. Pond conditions: The pond is required to be far from pollution sources, with an area of 5-10 mu, a flat pond bottom, and the bottom substrate is best as loam, with slight seepage being preferable, a bottom mud of 10-20 cm, and a water depth of about 2 m. Each pond should be equipped with one 3 kW impeller-type aerator and one 4-inch water pump, to be ready for timely water changes and aeration.

2. Cleaning and disinfection: Grass carp itself has many diseases, and ponds are even more prone to outbreaks of epidemics. At the same time, eliminating trash fish is an important measure to ensure normal feeding of grass carp and save feed. The specific method is, under dry pond conditions (with 5-10 cm of standing water), apply 100 kg of quicklime per mu, slake it into slurry, and splash it over the whole pond, or apply 10 kg of bleaching powder per mu, dissolve it in warm water, and splash it over the whole pond, making sure no dead corners or surfaces are left untreated, so as to thoroughly kill pathogenic bacteria.

3. Water quality requirements: The pond water quality requires a pH value of 7.5-8.5. During the peak farming period (June to September), the pond water transparency should be maintained at about 30 cm, and the organic matter oxygen consumption should be 18-20 mg/L.

II. Stocking of grass carp fry and fingerlings

1. Fry and fingerling selection: Grass carp fingerlings should be selected with a golden body color, no external injuries, lively and robust, and weighing about 100 g each. At the same time, because the two major diseases of grass carp, hemorrhage and enteritis, both easily infect fish fingerlings of the current year, in terms of fry and fingerling selection, 2-year-old fingerlings are preferable.

2. Fingerling stocking: Grass carp fingerlings are generally stocked at 800-1,000 per mu, paired with 100 silver carp fingerlings of individual size 250 g to 500 g. Do not pair with carp, or pair with few carp, to avoid competing with grass carp for food. In addition, before the fingerlings enter the pond, attention should be paid to disinfecting the body surface.

Ecological habits of grass carp

Grass carp generally prefer to inhabit the middle and lower layers of water bodies such as rivers and lakes and nearshore areas with abundant aquatic plants. It has the habit of river-lake migration. Sexually mature individuals spawn in flowing water such as rivers and reservoirs. After spawning, the parent fish and young fish enter tributaries and lakes connected to the river, usually feeding and fattening in submerged shallow grassy beaches and flooded areas as well as affiliated water bodies of the main and branch streams (lakes, small rivers, channels, and other areas overgrown with aquatic plants). In winter, they overwinter in the deep water of the main stream or lakes.

Grass carp is lively in temperament, swims rapidly, often forages in groups, is gluttonous, and is a typical herbivorous fish. At the fry stage, it feeds on zooplankton; at the juvenile stage, it also eats insects, earthworms, algae, duckweed, and so on; when the body length reaches more than about 10 cm, it feeds entirely on higher aquatic plants, among which grasses are especially common. The plant species eaten by grass carp vary somewhat according to the condition of the food base in the living environment.

How do grass carp reproduce

Grass carp (white amur). The reproductive situation of grass carp is similar to that of several other domesticated carps. Under natural conditions, they cannot spawn in still water. Spawning sites are generally chosen at river confluences of the main stream, deep-channel waters on one side of a river bend, and river sections where the banks suddenly narrow, as suitable spawning grounds. The reproductive season is similar to that of silver carp, slightly earlier than that of black carp and bighead carp. The reproductive period is April to July, relatively concentrated in May. Generally, when the river water rises early and fiercely, and the water temperature can stabilize at about 18°C, grass carp spawning reaches scale.

The reproductive habits of grass carp are similar to those of other domesticated carps. The ovary of grass carp that has reached maturity overwinters throughout the entire winter (December to February) at stage III of development; in March to April, when the water temperature rises to about 15°C, the stage III oocytes in the ovary quickly develop to stage IV, and reproductive migration begins. During the upstream migration process, development from stage IV to stage V is completed. During its upstream migration journey, if it encounters stimulation from hydrological conditions suitable for spawning, it spawns. Usually spawning takes place in the water layer, and the fish body does not float to the water surface, commonly called "quiet spawning"; but when excellent reproductive ecological conditions are encountered, such as a steep rise in water level accompanied by thunderstorms and heavy rain, then female and male fish chase each other in the upper layer of the water, showing the "floating display" phenomenon of lying on the back and trembling. After the egg is fertilized, because the egg membrane absorbs water and swells, the egg diameter can reach around 5 mm, drifting with the current, developing best at about 20°C, and hatching into fry in about 30-40 hours.

Feeding and management of grass carp

1. Feed feeding: Mainly feed pelleted feed, with a feed protein content of 28-32%, supplemented with green feed. Feed feeding follows the principles of "coarse first, fine later" and "four fixed and four observations". Generally feed 2 times a day, with the amount consumed within 2 hours and grass carp eating to about 80% full as suitable. After continuously feeding pelleted feed for a period, pelleted feed should be stopped for 1 week, and during the interval, raw grain feed should be fed. Usually pay attention to appropriately adding vitamins and other drugs to the feed, to avoid diseases such as hepatobiliary syndrome in grass carp causing large numbers of deaths.

2. Water quality management: Correctly use the aerator. From June to October, on sunny and windless days, turn on the machine to aerate for 2 hours every day from 1 to 3 p.m., and aerate at appropriate times in the early morning. On consecutive cloudy days, aeration should be started earlier. Add new water to the pond at appropriate times, and adopt the method of "small drainage and small inflow, multiple water changes" to gradually regulate water quality. From June to September, add new water once every 3-5 days, about 10 cm each time, and every 15-20 days, for each mu of water surface with 1 m water depth, use 10-20 kg of quicklime, slake it into slurry, and splash it over the whole pond once.

3. Disease control: Adopt the method of "coarse first, fine later, combining fine feed and green feed" for feeding, to control the occurrence of hepatobiliary syndrome in grass carp. Common diseases of grass carp include red skin disease, gill rot disease, and enteritis disease. Generally, a treatment method combining oral administration and external splashing is adopted. External splashing mainly uses disinfectants such as bleaching powder and chlorine dioxide, for 3 consecutive days. For oral administration, "Sanhuang powder" medicated bait has a relatively good effect. For every 50 kg of fish body weight, use 0.3 kg of Sanhuang powder (50% rhubarb, 30% golden cypress, 20% scutellaria root, ground into powder and mixed evenly) mixed evenly with flour paste and then mixed into the feed for feeding, for 3-5 consecutive days.

4. Timely harvesting: Timely harvesting large-sized adult fish for market is an important measure for high-yield grass carp farming. The main purpose is to reduce the fish-carrying capacity of the pond water body and promote the rapid growth of pond fish in the later period. Generally, harvest once at the end of July, harvesting in the early morning when the water temperature is lower.

How to prevent grass carp from getting sick

1. Grass carp hemorrhagic disease: This is a viral fish disease. The fish body surface is generally dark black with a slight reddish tinge, with bleeding under the skin and in the muscles, congestion in the oral cavity, lower jaw, top of the head, or around the eye sockets, and even protruding eyeballs and congestion at the base of the gill cover and fin rays. The main symptoms are: congestion on the body surface, gill cover, muscles, and intestinal tract. Sometimes these symptoms appear simultaneously, and sometimes only 1-2 symptoms appear. The mortality rate is extremely high. Splashing povidone-iodine over the whole pond and oral administration of Chinese herbal medicine preparations have obvious effects. Using vaccines for immune prevention has a significant effect; injecting fish fingerlings with inactivated vaccine can prevent it.

2. Grass carp gill rot disease: A bacterial disease, to which grass carp of all sizes are susceptible. If ammonia nitrogen, hydrogen sulfide, and so on in the water body exceed standards, then chemical or biological methods need to be used to reduce their concentration before applying medicine; methods such as splashing 150 g of 8% chlorine dioxide per mu, 250 g of 8% bromochlorohydantoin per mu, and 250 g of 10% povidone-iodine per mu according to each meter of water depth can be used, combined with the method of adding 1 g of vitamin C, 1 g of allicin, and 2 g of enrofloxacin or florfenicol per kg of feed for treatment.

3. Grass carp enteritis disease: A bacterial disease, to which grass carp of all sizes are susceptible. Splashing disinfectants and oral administration of drugs such as allicin and antibiotics are effective; prevention and treatment method: add 10-15 g of furazolidone per 50 kg of feed, make medicated bait and feed it, once a day, for 5-6 consecutive days.

With the in-depth research on fish farming technology, there are now relatively scientific techniques for farming grass carp, which to a large extent reduces the situation of grass carp death, greatly improves the survival rate of grass carp, and now grass carp disease prevention and control measures have also been further improved, thus reducing the probability of grass carp getting sick.