What is the reason for the low yield of river crab farming? What shall I do? How to increase production?

River crab is the most important freshwater crab in China, which has delicate meat, delicious taste and rich nutrition. due to its strong adaptability and wide range of culture, the breeding scale has increased rapidly in recent years, which has brought good economic benefits to farmers. And some river crab culture ponds appear low-yield phenomenon, some even serious losses, so what is the reason for low-yield river crab culture? What shall I do? How to increase production?

I. the reasons for the low yield of river crab culture

1. The quality of seedling is not strictly controlled.

The quality of seedlings is not strictly controlled, which lays hidden dangers for later production.

two。 Adverse weather effect

If there is a continuous ultra-high temperature (the average temperature is more than 32 ℃) and less rain from July to August, the accumulated temperature of the pond water body will increase sharply, which will seriously affect the molting growth of river crabs, and the high temperature will lead to the decay of aquatic plants, the deterioration of water quality and the phenomenon of a large number of dead crabs.

3. Lack of production management

The outstanding performance is the improper water quality control measures, the outbreak of cyanobacteria; the unreasonable planting and management of aquatic plants, the sharp decline of pond ecological function; the unscientific feed feeding, aggravating the deterioration of water quality; and the improper use of drugs, resulting in the death of river crabs.

Second, how to increase the production of river crab culture

1. Develop ecological crab culture

The desilting transformation of the aged crab pond should be carried out, and an independent intake and drainage system and supporting oxygen-increasing facilities should be built conditionally. Sophora flavescens, verticillium verticillata, Elorella verticillata and other varieties of aquatic plants were mixed to meet the needs of aquatic plants in all growth stages of river crabs. The mode of multi-species mixed culture of crab, fish and shrimp was adopted to increase the biodiversity of crab pond, make full use of water body and improve the comprehensive utilization rate of bait.

two。 Strictly control the quality of crab breeds

Crab species as far as possible to breed on their own or choose a nearby breeding base with good reputation to buy, try not to buy non-local crab species from a long distance. Crab species require neat specifications, strong physique, quick crawling, complete appendages, smooth body surface without damage, no dirt attachment. Crabs should be selected one by one before planting in the pond, and those of poor quality should not be put into the pond in order to improve the survival rate. Stocking density should be suitable, not simply pursue output, but should be based on market demand and improve specification quality.

3. Strengthen production management

(1) Water quality control

During the whole culture period, the water quality was kept fresh, the dissolved oxygen was rich, the transparency was controlled at 20-40 cm, the dissolved oxygen was above 5 mg / L, and the pH value was 7.5-8.5. The water level adheres to the principle of "front shallow, medium deep and post stable", that is, keeping shallow water level (www.nczfJ.com/) in the early stage to increase water temperature and promote crab molting, keeping deep water level in the middle stage, especially in hot summer and autumn, keeping the water quality fresh and sufficient dissolved oxygen, and keeping the water level stable in the later stage.

In general, the water is changed once every 15 days in spring and autumn, with a depth of 10 centimeters and 20 centimeters in depth. From June to September, the water is changed once every 5 days, and the depth of water is 10 centimeters and 20 centimeters deep. The old water in the pool is discharged first and then the new water is infused. Add about 20 centimeters of new water every day during the high temperature season to reduce the water temperature and ensure a good growth environment for river crabs. When the water quality of the crab pond is poor, timely water exchange or other measures should be taken to improve the water quality. From May to September, microbial preparations were applied every 10 to 15 days, and then fertilized properly according to the water quality. In addition, quicklime was applied once every 15-20 days, and the dosage was 10-15 kg / mu rice. After pulping, the whole pond was evenly sprinkled to regulate the water quality, increase the content of calcium ion in water and promote the normal molting growth of river crab.

(2) feeding management

In the whole breeding process, scientific feeding is required to ensure balanced nutrition, mainly feeding river crab formula feed, snail, chilled fish, with a small amount of plant feed such as wheat, soybean meal, corn and so on. Daily feeding should "master a method, adhere to a principle, and highlight a key point", that is, the scientific feeding method of "four determinations and four views", the principle of "combination of fine and green, the combination of meat and meat" and the focus of "early essence, middle stage, late stage meat". The specific operation is: on the premise of ensuring that the feed is fresh and palatable, the daily feeding amount depends on the weather, water temperature and crab intake.

In the early stage of culture (March to June), bean cake, wheat flour, silkworm pupa meal, fish meal or chopped fish, minced snail and clam meat were mixed and fed into a ball, or mainly fed with open compound feed. In the middle period of culture (from July to mid-August), bean cake, corn, wheat, potato, pumpkin and other fine and green fodder were the main. In the later stage of culture (late August to November), the proportion of animal feed (animal feed accounted for 50%) or special compound feed for river crab was appropriately increased. In general, the daily feeding amount from March to April is 1% of the body weight of the pond crab, 2% of the body weight of the pond crab, from May to July is 3% of the body weight of the pond crab, from August to October is 8% of the body weight of the pond crab. The feeding frequency was 1 / day in the early stage, 2 / day in the middle and late stage, 30% in the morning and 70% in the evening. Concentrate feed and fresh feed are fed alternately every other day or every other meal, evenly in the shallow water area, insist on checking the eating condition every day, and it is appropriate to finish it 3-4 hours after feeding.

(3) Management of aquatic plants

Ensure that the density of aquatic plants is reasonable, "take the lead" treatment should be carried out when the growth is too prosperous, and duckweed should be properly stocked in summer. From February to March, the work of fertilizing water should be done well, and the water level should be properly controlled to increase the water temperature and promote the rooting and sprouting of aquatic plants.

4. Strengthen disease prevention and control

The susceptible diseases of river crabs should be prevented as soon as possible, drugs should be used scientifically, and they should not be treated at random, resulting in unnecessary losses. The occurrence of river crab diseases can be effectively prevented by adopting ecological culture technical measures, such as strict disinfection of ponds, stocking of strong crabs, keeping good water quality in ponds, and feeding fresh and high quality feed. In the high temperature season, microbial agents were sprinkled in the whole pond every 10-15 days, and quicklime was applied alternately to improve the water quality and bottom quality of crab ponds and ensure the healthy growth of river crabs.

After the occurrence of diseases, the bacterial diseases of river crabs can be evenly sprinkled with disinfectants with high efficiency and low toxicity, such as bromochlorohydantoin, chlorine dioxide or iodine, etc., and feed with appropriate amount of norfloxacin, allicin, vitamin C, immune polysaccharides, etc.; for ciliosis, it can be sprinkled evenly in the whole pool after dissolving with water, such as Xianchongjing, chitin and other drugs. In addition to taking corresponding treatment measures, attention should also be paid to the restoration of crab ponds to ensure a good growth environment. The specific methods of water remediation are as follows: after 2-3 days of good results in the treatment of river crab disease, the water quality protection antidote was sprinkled once in the whole pond, and then biological fertilizer and appropriate amount of microbial preparation were applied appropriately according to the water quality.