Li Hechun, a villager of Lioutou Village, Guxi Town, Gaochun County, Nanjing City, has a small culture. He has been engaged in aquaculture in the village of Yonglian for many years, and his crab breeding area is 70 mu. At the beginning of this year, the heavy snowfall in Gaochun County, Nanjing, which had suffered for a long time, coupled with prolonged low temperatures in early spring, had a great impact on water production. However, Li Hechun made a fuss about the regulation and control of the aquatic environment of crab farming and carefully managed his crab breeding in 2008. Acquired 41 kilograms of crabs per mu, with an average size of 190 grams/piece, and an average gross profit of 2550 yuan per mu, which achieved good economic benefits.

In the process of crab aquaculture production, the survival and growth of the crab is greatly affected by the water quality and environmental factors. The so-called “crab raising is water conservation”, which shows the importance of water quality management in crab breeding. Although the crab breeding pond itself has the ability of self-purification, it can decompose the organic matter into the nutrient source for the growth of the crab. However, when the excessive organic matter input exceeds its self-purification ability, it will inevitably cause changes in water quality and sediment quality, and thus affect the survival and growth of the crab. . In order to better improve the aquatic environment of river crabs, Li Hechun mainly adopted the following technical measures;

First, dredging and disinfection

Organic matter in mariculture ponds and humus silt are often the root cause of water quality deterioration and induced disease occurrence. In the period of November-December, when the pond products were sold, promptly clean up the ditch and ponds, remove excess silt from the bottom of the pool, and use the quicklime or bleaching powder to spill the entire pond for disinfection, exposure, and complete killing of various pathogens. Before the Spring Festival, we will plow the fields in the middle of the pool and apply fermented pig manure to fertilization fields. This will help reduce self-pollution, improve water quality and sediment quality, and prevent the occurrence of crab diseases.

Second, transplanting plants

Practice has proved that the role of aquatic plants is very large. First of all, it is a high-quality crab diet, rich in vitamins and calcium, phosphorus, can promote the proliferation of benthic organisms, and has a greater effect on the shelling of crabs. Secondly, it can shade and cool the temperature. The water temperature in grassy ponds and grassless ponds can be more than 5°C in the high temperature season in summer. The water plants can also effectively absorb the ammonia nitrogen in the water and prevent the water quality from becoming too fat. In addition, it can also absorb suspended particles in water to increase transparency. The aquatic weed mainly includes black algae, Vallisneria and Elodea. The crab breeding process should allow aquatic plants to coexist and distribute in a variety of ponds, accounting for about 70% of the pond area.

Third, timely fertilizer

The cultivation of aquatic grasses, snails, and plankton in crab ponds requires large amounts of nutrients. Spring is dominated by organic fertilizer, urea and biological fertilizers. In the high temperature season, compound fertilizers and bio-fertilizers are mainly used. Throughout the breeding process, water quality is always maintained, and the water body has sufficient dissolved oxygen.

IV. Transplantation screw

In the winter and spring season, about 400 kilograms of fresh snails will be released per acre after the clear pond, which is appropriate for three batches. The live snail can loosen the bottom soil, accelerate the release of inorganic salts of the sediment into the water, and can also remove organic waste such as bait in the pond. The snail meat is rich in calcium and phosphorus, which can promote the growth and shelling of the crab.

Fifth, change the water frequently

The majority of farmers understand the truth of “the spring is shallow and full in summer, and the autumn is deep in autumn and winter”, and usually pay attention to the depth of water. In the breeding process, it is a better method to maintain regular water injection and create micro-flowing water to breed crabs. Adding water should be done in the early morning or in the morning. It should not be added in the evening. In case of cloudy days, abnormal eating of crabs, and high-temperature weather, the amount of water exchange is increased, so that water quality, water temperature, and dissolved oxygen can all be kept at a good level, which is conducive to feeding and utilization of feedstuffs for crabs.

Six, the use of microbial agents

After entering into June, it is a period of extensive application of microbial preparations in crab ponds. It is also a period of good application of microbial preparations. It can be regularly applied to crab ponds, and is usually applied once every 7-10 days. The principle of the application is to use the beneficial bacteria in the biological preparations to enter the aquaculture water and exert their functions such as oxidation, ammoniation, nitrification, denitrification, phosphorus release, sulfidation and solid ammonia, etc., and excrete, residual feed, and biological residues of crabs. The organic matter such as the body rapidly decomposes into carbon dioxide, nitrates, phosphates, etc. to provide nutrition, promote the growth of aquatic plants, and rapidly reproduce itself to become a dominant strain, thereby resisting the growth of pathogenic bacteria and regulating the water quality to maintain a good ecological environment for water bodies. To achieve the effect of preventing diseases.

During the later period of cultivation, especially during the high temperature season, the non-oxidative decomposition of organic matter in the crab ponds is deposited on the bottom, and it is easy to form a black muddy area and produce toxic substances such as ammonia nitrogen and hydrogen sulfide, which deteriorate the water quality. The improved method is to spit lime regularly and use a bottom modifier. The use of lime can increase the pH, make the water weakly alkaline, and can promote the release of nitrogen, phosphorus and other nutrients in the sediment into the water; the use of the bottom modifier is a catalyst that can improve the conversion efficiency by using modern biotechnology. The mud-water interface layer serves the purpose of improving bottom quality and water quality.

Li Hechun's crab breeding can achieve very good results, mainly due to the fact that he usually pays great attention to the changes in the water color of the pond, and then timely passes through the fertilization, planting grass, putting snails, replacing new water, splashing microbial preparations, etc. according to the water quality. The measures to maintain good water quality in the pool and create an ideal ecological environment for crab growth are important reasons why his breeding has been successful for many years.

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