.1 Features and Advantages of Yangtze River Water Crabs The crabs have light yellow, elliptical and sharp lateral flanks. The fourth side teeth are obvious, and the central depression of the front teeth is obvious. The second foot and the second foot are equal in length. The ratio of the fourth side tooth to the first foot is 1:20 (this ratio is the key difference between the Yangtze river crab and other river crabs). The step is golden yellow, and the second is not. bristle. The advantages of the Yangtze River Crab are many, the biggest advantage is that the growth rate is fast, individual crabs are significantly larger than other water systems.
1.1.2 Parents' preferred selection order: Yangtze River> Lake> Pond
1.1.3 The preferred selection order for aquatic fingerlings is: natural (harvested) Yangtze River waters Chinese mitten crabs> artificially-breeded Yangtze river waters Chinese mitten crabs> artificially grown Yangtze Rivers with large crabs as their parents Aquatic Chinese mitten crabs.
1.2 The quality is good
1.2.1 Correctly identifying precocious crab species and raising the survival rate of crab species. Precocious crab species refer to the crabs of the current year. After being cultivated into the crab species of the current year, individuals are small, usually about 20 grams, and the gonads have matured. Crab. The use of this crab species for commercial crab production for the following year has caused most of the deaths due to difficulties in oyster shells, which has brought serious economic losses to crab production. There are four ways to correctly identify precocious crab species:
(1) Look at the abdomen of crab species. If the abdomen of the female crab has become almost round, that is, it has been presented with a umbilicus, the villi around the umbilicus, and the fourth and fifth quarters of the plastron have become wider, indicating that the crab has become precocious; If you have developed into a white, hard, osteogenic tube, this male crab has been sexually mature.
(2) Look at the chelipa of the crab species, and if there is no fuzz on the medial aspect of the foot, if it does not, it is not a continuous fine and short hair; precocious crab species chewing foot or step foot villus thick and long, color Deeper.
(3) Look at the color of the head breastplate and the crab pattern. The back color of the normal crab head breastplate is light yellow, while the back of the sexually mature crab species is dark green or blue; the back of the normal crab species is relatively flat and undulating, while the back of the sexually mature individuals is uneven.
(4) Look at the gonadal development of crab species. Open the head breastplate. If there are two purple strips on the liver, and there are even granules, then it is a sexually mature ovary; if there are two white strips, it is a mature testis. If only the yellowish liver is seen, the gonads are immature.
1.2.3 The best condition for self-breeding crab species.
Self-breeding crabs have high survival rate, strong resistance to disease, rapid growth, and their quality is significantly better than that of purchased crabs.
2. Crab Pond Disinfection Disinfection Crabs like to inhabit rivers, lakes, muddy shores or mudflats, or hide in gravel and water plants. In artificial breeding, the burrowing characteristics can be changed. According to the survey, the ratio of burrowing crabs in breeding ponds is relatively low, and females are more than males. The vast majority of crabs are buried in the sediment. Only the eyes and tentacles above the exporter are exposed and the breath is maintained. We believe that the quality requirements for sediment are also a key factor in large-scale crab production. At present, the key to the pathogenesis of crabs lies in the cleanliness of sediments. In production, we can take the following measures to improve and improve the quality of bottoms to meet the growing needs of river crabs.
2.1 After the end of each year, all ponds mostly pass through dry pond dredging (less than 15Cm sediment) and after exposure, 100-100 Kg/mu quick lime clear ponds are used.
2.2 Thorough dredging can be achieved by means of underwater dredges.
2.3 Oxygenation of flowing water or aeration of oxygen by using aerators to ensure that the dissolved oxygen in the water is not less than 5mg/L.
2.4 Efforts to promote the use and feeding of photosynthetic bacteria and other microorganisms can effectively absorb water and bottom toxic substances. Its role is as follows:
(1) Purify water quality, significantly improve the water environment (absorb hydrogen sulfide, ammonia and other toxic substances), and reduce their concentration in water;
(2) It can effectively increase dissolved oxygen and stabilize PH value in water environment;
(3) photosynthetic bacteria itself is a high protein (content up to 65%), can significantly increase the crab production;
(4) can effectively improve the crab body immunity;
(5) can reduce production costs;
(6) It can produce green products and pollution-free products.
3. Adjust the stocking mode
3.1 The appropriate density.
Change the rearing to thin, 500-600 birds/mu, so that the crabs have ample living and growth space.
3.2 Moderate specifications.
壹 壹 为 为 为 — — — — — — 100 100 100 为 100 。 。
3.3 Timely stocking.
Change the winter to release it for the spring and the quail-like period from the end of February to the beginning of March, when the water temperature is 8-12 °C.
3.4 After stocking, raise them first.
"Temporary care" is a transitional phase that must be provided before stocking crabs. After the crabs have been raised and raised, they can greatly increase the survival rate of the pond. Pay attention to the length of the holding time, depending on the water temperature and the growth of aquatic plants in the pool.
4. Planting aquatic plants Planting aquatic plants is a very effective method that is vigorously promoted in ecological crabs today. As the saying goes: "Crab size, look at plants."
4.1 The main purpose of planting aquatic weeds is to disperse the water. It can make full use of water bodies and make use of the three-dimensional benign distribution of crabs, that is, the distribution of upper, middle and lower water bodies is suitable.
4.2 The species of aquatic plants can choose Elodea, Vallisneria, Hydrilla verticillata, etc., but Elodea is the best, its nutritional value is high, and its vitality is very strong, and it can grow in the following four seasons.
4.3 The area of ​​grass is controlled at about 60% of the water surface. If it is too dense, it is necessary to open a channel with a width of 3 to 5m every 10 to 15m to ensure that there is enough light at the bottom of the pool.
4.4 It is not too early or too late to choose the kind of grass time before and after Ching Ming.
4.5 Planting Methods Elodea and rotifers are mainly vegetatively propagated. The method of cutting the stems and cuttings in sections is used. The dosage is 25-30 kg per mu, and the seedlings are mainly sowing grass. The amount per mu is 0.1 kg.
4.6 Management points (1) Fertilization should be carried out in a timely and timely manner (compound fertilizer and basal fertilizer should be enough; inorganic fertilizer should be moderate, and efforts should be made to promote the use of calcium dihydrogen phosphate).
(2) The planting of aquatic plants should be carried out before the stocking of crabs. It is ensured that the crabs grow in front of the ponds. Otherwise, the shoots of the grass are eaten by the crabs and affect the growth of the plants.
5. Improve the feeding quality of aquaculture technology Feed quality is a material guarantee for the production of crabs and crabs.
In March, when the water temperature reached 10°C or more, it began to be fed. Baits mainly include animal carcasses and their slaughtered leftovers, carcasses, snails, and shrimps, as well as grasses such as wheat, cereals, cakes, aquatic or terrestrial fresh. Feeding must adhere to the principles of fine, green, and coarse matching. From April to May, the aquatic plants in the pond germinated, and the bio-feed was alive. The freshly-discharged crab species were small and the water temperature was low. The crabs did not have high feeding intensity, and they could feed animal feed less and cast more green or roughage. From June to October, the individual crabs gradually grew up and the water temperature increased. The feeding intensity of the crabs was large. Especially from August to October, the crabs were fattened and yellowed, and the body weight increased significantly. More animal feed should be fed. Every day before and after the evening feeding, the feed was placed in the shallow water near the pool, and a multi-point food table was set up. Each feeding amounted to about 10-20% of the total weight of the crab, and it was appropriately increased or decreased depending on the season, water temperature, weather, food intake, and growth. In addition, in the actual operation should also pay attention to the following aspects.
(1) During the Ching Ming period, more than 300 kg of live snails, etc., should be put into use as a basic bait throughout the year.
(2) feeding to achieve timing, positioning, qualitative, quantitative.
(3) When artificially preparing a mixed feed, it is best to make the feed into a shape like noodles or lumps to facilitate the feeding of crabs.
(4) Feeding wheat, pumpkin, cereals, cakes, etc. during the early stage of the growth of crabs. During this period, it is recommended to feed malt (malt feeding will ensure that it will not rot or deteriorate for 1-2 days), and the remaining feed should be cooked. Feeding.
(5) The crab's breeding should be repeated several times. The enlargement of the body, the change of shape, and the regeneration of the broken limb are all formed after each clamshell. The oyster shell runs through the entire growth and life of the crab. Therefore, it is necessary to properly feed capsella, and the feeding of capsin and feed should be appropriately separated in terms of time. In addition, during the crab shell, it is necessary to constantly renew the water and maintain micro-flowing water, which can effectively stimulate The crab shell.
(6) During the entire breeding cycle, appropriate amounts of lime should be splashed and used to purify the water. In addition, calcium should be added to the water body in order to prepare multiple clam shells.
6. Scientifically conditioned water quality Healthy crabs have a very high quality requirement for the water environment and must be scientifically conditioned.
6.1 Water quality indicators require transparency of 35-40 cm, dissolved oxygen above 5 mg/L, pH value of 7.5-8.5, and ammonia nitrogen concentration of 0.2-0.5 mg/L. The above water quality indicators can be clinically tested through the use of water quality test kits, which will take some measures (mainly to simulate the natural ecological environment) to carry out necessary, beneficial, and timely control of the water environment.
6.2 Pool Water Regulation
At the beginning of the end of February and early March of the crab species, the water depth is controlled at 0.6-0.8 m, the water depth is between 0.8-1.0 m during May-July, and the water depth is between 1.0 m and 1.2 m during the period from August to October. In the spring and autumn, change the water once a week, each time deepen 30-40 cm. When changing the water, it is necessary to perform side-by-side irrigation. Do not change the water temperature by more than 5°C. Such as pool bottom silt more, low transparency, water color becomes thicker, crab back a dark, rust appears on the abdomen, step foot turn yellow, fresh lime 7.5-15 kg per acre, into the water Quanchiposa, continuous Use 2-3 times, each interval of 5-7 days, can adjust the water quality, increase the concentration of calcium in the water, is conducive to the growth of crab and crab shell color changes.
6.3 Precautions
(1) Change the water and change the amount of water in time to improve the environment and reduce the temperature. The appropriate water temperature for crabs is 25-28 °C.
(2) The stone is not suitable for multiple use, reuse, and common use. If used frequently, the hardness of the water body will be too large, the dissolved oxygen will decrease, and the phosphate concentration will decrease.
(3) In order to maintain the fatness of the pool water, the organisms such as snails and baits are encouraged to grow.
(4) Implement polyculture of crab fish. The mixed use of crab and fish can make full use of the water space, improve the utilization of feed, purify the water, and effectively improve the water quality of the pond. However, it is necessary to use mainly crabs, which can be adapted to stocking a small amount of earthworms, earthworms, grasses, cockroaches, and tilapia, but it is not possible to stock fish such as earthworms and herrings. Pay attention to escape.
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