After more than 30 years of development, the river crab breeding industry has now become one of the pillar industries of aquaculture in China, basically forming a complete industrial chain of river crab seedlings, crab breeding, adult crab breeding, crab product processing, export foreign exchange, etc., and the breeding area, output, output value and trade have increased steadily year by year. Due to the imbalance in the level of river crab breeding technology in various places, the benefits of river crab farming fluctuate greatly. Based on years of technical accumulation and summary, the author puts forward the following key technical points in the whole process of ecological and healthy breeding of river crabs for the reference of the majority of farmers.
1. Water source. Before choosing a crab farming base, it is necessary to have a full understanding of the water source, sufficient water is the prerequisite, and the breeding area should be far away from industrial, agricultural and domestic pollution sources. Large-scale farms should set up wastewater purification treatment facilities (such as ecological warm land, ecological purification ponds, etc.), and wastewater discharge should meet the "Freshwater Pond Aquaculture Water Discharge Requirements" (sc/t 9101-2007) standard. Crab ponds must be built separately inlet and drainage to prevent the discharged water from entering the inlet. The inlet of the water must be equipped with a stainless steel or screen mesh filter device of 60 to 80 mesh to prevent wild trash fish and shrimp and other predators from entering.
2. Water quality. The water quality has no color, odor and odor, and 12 indicators such as total E. coli have been tested to meet the standards of "Pollution-free Agricultural Products Environmental Conditions for Freshwater Aquaculture Production Areas" (ny 5361-2016). It is best to set up pretreatment equipment or facilities for aquaculture water (such as water storage purification ponds, etc.).
3. Dredging. Due to the bait fertilization and excrement of farmed animals, a large amount of residual bait, fertilizer residue, manure, carcasses and organic debris are deposited at the bottom of the pond. At the end of one culture cycle, drain the pond water, using manual or mechanical, remove excess silt from the bottom of the pond to reduce the accumulation of toxic and harmful substances at the bottom of the pond.
4. Sun pond. Drain the pond water, let the pond be completely exposed to the sun, through the winter freezing and sun exposure for about 1 month, so that the bottom of the pool to crack, promote the decomposition of organic matter at the bottom of the pool into nutrients, let the toxic and harmful substances decompose, volatilize, reduce the harm of bacteria, parasites and other harmful organisms.
5. Disinfection. Crab species must be thoroughly disinfected with drugs before stocking, commonly used drugs are quicklime, bleaching powder and tea meal, etc., the dosage per mu is 75 to 100 kg, 30 to 75 kg and 30 to 50 kg, and can also be disinfected by the method of quicklime or bleach powder + tea meal.
6. Plant grass. Aquatic grass can not only be used as part of the bait for river crabs, but also can absorb and utilize nutrient salts such as nitrogen and phosphorus in the water, and can also provide a hidden place for molt crabs to avoid killing each other. The aquatic weed varieties grown in crab ponds include Elek algae, black algae, bitter grass, duckweed and water peanut, etc., which have advantages and disadvantages. Elezae can grow at temperatures above 5 °C, in the cold winter can be overwintered with nutrients, when other aquatic plants have not yet sprouted, Elezae has begun to grow normally, its disadvantage is not high temperature tolerance, easy to rot roots. Rotifer-leaf black algae is highly adaptable, easy to plant, fast growing and high yield. Bitter grass is suitable for crab pond planting with thick bottom mud, forming an "underwater forest", the disadvantage is that crabs like to clip new and old grass leaves, floating on the surface of the water must be manually removed, otherwise it will rot and corrupt the water quality. Through the set of seeds, you can give full play to the strengths and avoid the weaknesses, and give full play to the advantages of each variety of aquatic plants. In the early days, it was dominated by Elegae, summer and autumn were dominated by rotifer black algae and bitter grass, and later by rotifer black algae, duckweed and water peanuts as supplementary aquatic grass varieties.
7. Throw snails. Snail is a high-quality natural food for river crabs, and also has the role of purifying water quality by using the nutrient salts of crab ponds. 400 to 500 kg of live snails are stocked in 2 to 3 times per acre of crab pond, which requires freshness and cleanliness, and must be stocked once before Qingming to breed small snails for the newly stocked crab species to feed. The snail is locally produced, long-distance transportation affects the survival rate, and too much one-time release is easy to cause water quality to be thin, resulting in the breeding of moss.
8. Fertilizer water. The role of fertilizer water is to maintain good water quality, is conducive to the consumption of organic matter, provides rich natural food organisms for shrimp and crabs in winter and spring, promotes the growth of aquatic grasses, and inhibits the reproduction of moss. 15 days before the release of crab seeds, 200 kg of fermented and decomposed organic fertilizer and 2 kg of compound fertilizer are applied per mu of water surface as base fertilizer, and then depending on the water quality and leanness, compound fertilizer is sprinkled every two weeks, 1 kg per mu. During the low temperature period, instant fertilizer fertilizer water should be selected, otherwise it cannot be directly absorbed and utilized by algae and aquatic weeds; fertilization should be applied in small quantities to avoid a large number of rotifers and branches; fertilization should be selected in the morning, and the fertilizer should be sprinkled in the whole pond after mixing with water.
9. Selection. Select the crab seedlings propagated by the purified and rejuvenated broodstock in the Yangtze River system, and it is best to set up a special pond for self-breeding crab species in large-scale farms or adult crab areas, so as to know what is in mind and avoid long-distance transportation. Purchased crab seeds must be inspected at the nursery to understand the water quality of the breeding pond, the environment and the incidence of diseases and drugs during breeding, and the crab seeds must be quarantined at the place of origin to ensure health and disease-free.
10. Stocking. Crab species size of 100 to 160 crabs per kilogram, stocking amount according to the design yield and specifications of the situation flexible grasp, generally 600 ~ 1500 / mu. The specifications of crab species stocked in the same pond are basically the same, requiring that the internal organs of crab species be normal, the appendages are complete, and there is no claw grinding phenomenon. Stocking is from the end of February to the beginning of March, and it is selected on sunny days. In advance, the temporary area, which occupies about 10% of the total area, is fenced with nets, and the water weeds are planted in other areas, and the fence is dismantled before the end of May after the water weeds grow luxuriantly. Before stocking crab species, 10 grams of potassium permanganate solution is added to 10 kg of water and bathed for 5 to 10 minutes to kill pathogenic microorganisms such as parasites and bacteria on the surface of the body.
11. Polyculture. In order to make full use of the water body space and avoid the risk of single crab farming, crab ponds can mix some fish and shrimp that do not conflict with river crabs, such as green shrimp, tropical shrimp (P. vannamei and Giant river prawns), slender-scaled oblique jawed mandarin, bighead carp, pond mandarin fish, mandarin fish, etc. Green shrimp can be reared in the wrong season with river crabs, South American white shrimp and giant river prawn can be "double-headed" with river crabs, fine-scaled obliquely jawed sea bream and bighead carp can feed on mud moss and zooplankton in crab ponds, and pond mandarin fish and mandarin fish can control wild trash fish and shrimp in crab ponds.
12. Feeding. River crab is an omnivorous animal, the feed has "meat, fine, green" points, meat materials mainly include snails, mussels, clams and sea, freshwater small miscellaneous fish, etc., concentrates have compound feed, wheat, corn, etc., green materials include planted aquatic grass and pumpkin, potato shreds, etc. Feeding requirements "before and after the fine, medium and coarse", adhere to the qualitative, quantitative, timed, fixed point of the "four fixed" principle, generally before May every day at 5 pm feeding once a day, starting from May, 2 times a day, the first time in the morning 8 ~ 9 o'clock, accounting for 30% of the daily amount of the place, the location in the deep water area; the second time in the afternoon 5 to 6 o'clock, accounting for 70% of the daily amount, the location in the shoal area.
13. Pipe water. River crab farming Longqi is a shrimp and crab polyculture pond, advocating the principle of "early fertile water, medium and late water", which is conducive to controlling moss and promoting the growth of shrimp and crabs and aquatic plants. The water level of the crab pond is 30 cm in March, and then increases by 10 cm per month, and the pool water reaches 90 cm in September, and the maximum water level can be increased to more than 110 cm in case of continuous high temperature. Before the end of June, the main water is added, 10 to 20 cm each time, the high temperature period from July to August, replace the new water every 10 days when conditions permit, 10 to 20 cm each time, change the old water at the bottom in the early morning, prevent the temperature difference from being too large to produce stress, and the river crab molting and changing the water during medication should be avoided. Maintaining sufficient dissolved oxygen is the key to pipe water, and it is particularly important to increase oxygen in the rainy season, and it is best to install microporous tube aeration facilities in crab ponds with conditions. Water quality indicators should be mastered dissolved oxygen above 5 mg / l, ph value 7 ~ 8, transparency 30 ~ 50 cm, ammonia nitrogen 0.2 mg / l and nitrite below 0.02 mg / l. It is generally regulated by sprinkling quicklime, bacillus, em bacteria, etc.
14. Change the bottom. Due to the increase in harmful substances such as hydrogen sulfide, ammonia nitrogen, catalate, and heavy metals in the silt at the bottom of the pond due to residual bait, animal carcasses, and decomposing aquatic weeds. In the breeding process, especially in the middle and late stages, substrate modifiers are used every 10 to 15 days, such as decomposition type bottom modification, Bacillus, Vibrio vermicularis and other biological products.
15. Grass protection. Aquatic weed management is the top priority of crab management. The growth characteristics of each species of crab pond aquatic grass are: the early stage of The algae with the increase of the water level, the growth is very vigorous, around the end of June into the decay period, should be cut off in advance, after cutting can break the dormant state at high temperature, and restore the vigorous growth force. The early growth of black algae and bitter grass is slow, and the growth of high temperature season is accelerated, but excessive growth will cover the water surface, and even the bottom of the water has no light, and the pond cannot form wind and waves, which is not conducive to increasing the dissolved oxygen of the pond, so it is also necessary to take artificial control measures such as cutting and thinning. When cutting grass, we should pay attention to avoiding the peak period of molting and the period of poor growth status of aquatic grass, disinfect and transfer water in time after cutting grass to care for the wound of aquatic grass, so that it can restore growth as soon as possible, and can also be cut in batches, until the aquatic grass is first cut to resume growth, and then cut another batch. It is also necessary to properly handle common problems such as long foliage hairs, long scale on the leaf surface, rotten roots, small stems and leaves, and damage of grass worms.
16. Disease prevention. The prevention and control of river crab diseases should follow the principle of "focusing on prevention rather than treatment". Disease prevention work should take the road of immunization, ecology and green prevention and control; in the event of diseases, adhere to the right medicine, select high-efficiency, low-toxicity, no residue-free green fishing drugs, avoid the use of antibiotics and chemical agents with high residual toxicity, and put an end to the use and abuse of illegal fishing drugs. In the process of breeding, it is necessary to grasp the key links such as clear pond disinfection, selection of medicinal baths, planting grass and snails, selection of materials for fine feeding, water diversion and bottoming, and regular medication prevention, and implement ecological healthy breeding.
17. Eliminate harm. The predators in the process of river crab farming are mainly black, rodent and wild miscellaneous fish and shrimp. Anti-bird nets, color strips, scarecrows and other facilities can be set up to intimidate and drive away water birds. Before stocking, completely remove predators with drugs, filter the water inlet to prevent predatory organisms from entering, and strengthen prevention and removal of predatory organisms at ordinary times.
18. Fishing. The best season for river crab fishing is from mid-October to early November, if the catch is too early, some river crabs have not yet completed the mature molting shell; and too late, due to the cooler climate, river crabs due to reproductive migration, very easy to escape, some of the pond river crabs will also burrow over the winter, not easy to catch. Fishing methods include ground cage, freehand capture, light trapping and flowing water fishing.
19. Temporary rearing. For the caught commercial crabs, those that are too late to sell or are left to be sold when the market is scarce, or exported for export, need to be concentrated for temporary breeding. The advantages of temporary breeding: first, it is convenient to concentrate and sell long distances; second, through temporary breeding, it can be sold at a price, making full use of the seasonal price difference in the market and selling to a good price; third, through temporary breeding, it can be fattened and weight-increased, so that some commercial crabs that have recently molted their shells can achieve the purpose of weight gaining and fattening by feeding small miscellaneous fish, soybeans and other high-quality feed. According to the number, requirements and length of temporary breeding time of commercial crabs, the temporary breeding method selects appropriate temporary breeding tools, and prepares temporary breeding facilities such as crab cages, crab baskets and cages in advance, selects a good technical scheme, and implements scientific temporary breeding to improve the survival rate of river crab temporary breeding.
20. Transportation. Before the transportation of commodity crabs, it is necessary to do a good job of "four separations" of size, strength and weakness, disability and fat and thin, and then select the appropriate packaging tools according to the transportation and sales methods, and indicate the grade, specifications, males and females, net content, producer name and address, packaging date, batch number and product standard number. The means of transport should be cleaned and disinfected before loading, so that it is clean, non-toxic and odorless. During the transportation process, it is necessary to prevent temperature changes, extrusions and sudden vibrations, and shall not be mixed with harmful substances to prevent transportation pollution.