Discussion on Water quality Control of River Crab Culture in South Jiangsu

This post was last edited by fishfirst on 2009-11-27 09:23 □ Wen/Wuxi Green Water Source Biotechnology Co., Ltd. Yang Xiuhua crab is known as "the top grade in the water, soup feast dishes", deeply loved by consumers at home and abroad. Under the new situation of developing high-quality, high-efficiency and high-yield fishery at present, crab breeding industry has changed from "large-scale crab breeding" in pursuit of yield to "large-scale crab breeding" and "ecological crab breeding" centered on quality and benefit. Crabs with small specifications and poor quality are increasingly unpopular with consumers. Large-scale and ecological crabs are not only sold smoothly, but also have absolute advantages in price. However, Chinese crab culture technology is still in the groping stage from rough to fine, and there are still many technical problems to be studied and solved. As the saying goes: "fish first raise water", this is also applicable to raising crabs, a pool of good water to raise a pool of good crabs. Adult crab culture is mainly completed in fresh water, from the beginning of each year to the end of August is the key period for adult crab culture, during which water quality control is the key to annual yield. In July this year, the author participated in the after-sales service in Nanjing Gaochun and participated in the production labor of part of the breeding pond mouth. Now, the water quality regulation of adult crab breeding is summarized, hoping to help crab farming production in the future. The pH value of pond water is an important indicator to judge whether the water quality is good or bad, generally needs to be controlled between 7.5-8.5, too high or too low, there are direct hazards to aquaculture, and even cause death. pH value lower than 7.0, weaken the ability of aquatic animals to carry oxygen in blood, resulting in crabs physiological hypoxia. Quicklime can be used to splash the whole pool regularly to improve the pH value of the water body, but pay attention to avoid splashing during molting period. The pH value of crab ponds will increase due to the large consumption of carbon dioxide by algae for photosynthesis, resulting in the decomposition of bicarbonate in the water, producing carbon dioxide and hydroxide ions, consuming acidic substances, and increasing the pH value. pH value higher than 9.0 may lead to gill corrosion, so that crab lost its respiratory ability and died, and pH value increased at the same time, ammonia toxicity also increased. To reduce the pH value of water body, first observe the color of water, control the amount of algae, and remove organic matter in time. When the pH value is too high, it is recommended to adjust the water depth of 1 meter per mu with acetic acid 2-3 jin, or alum. Dissolved oxygen maintains sufficient dissolved oxygen in the water to inhibit chemical reactions that generate toxic substances, convert and reduce the content of toxic substances (such as ammonia, nitrite and hydrogen sulfide). The dissolved oxygen required by crabs is 5-8mg/L, and the minimum is above 4mg/L. Although mild hypoxia did not lead to death, it caused irritability, accelerated respiration and slowed growth rate. The crab began to float at 2.5 mg/L and died of asphyxia at 1.5 mg/L. Oxygen-increasing agent should be applied in time when the crab is anoxic. Generally, there is no high dissolved oxygen during the breeding period, and the high dissolved oxygen has little effect on the crabs living at the bottom. Ammonia nitrogen includes the total amount of non-ion ammonia and ionic ammonia, almost all algae can quickly and preferentially use them, the disadvantage is that nitrification consumes dissolved oxygen, especially non-ion ammonia, which has strong toxicity to crabs, even if the concentration is very low. Generally, the ammonia nitrogen concentration in the pond does not exceed 0.1mg/L, and if it is lower than 0.05mg/L, it indicates that the water quality is relatively thin, and it is necessary to apply fertilizer in time to cultivate high-quality biological bait; if it is higher than 0.2mg/L, it can use Bacillus biological agents to reduce the ammonia nitrogen content. Nitrite is generally an intermediate product produced in the process of converting ammonia nitrogen into nitrate, which is hindered in the process of converting ammonia nitrogen into nitrate, and the intermediate nitrite will be produced in the water body. The existence of nitrite makes ferritin in crab blood oxidized into methemoglobin, thus inhibiting the oxygen carrying capacity of blood. Long-term high nitrite environment, affecting its feeding and growth, generally need to be controlled below 0.1mg/L, too high water must be timely use of nitrifying bacteria degradation substances. Hydrogen sulfide is more toxic to crabs than to conventional fish. Hydrogen sulfide is generally produced at the bottom of the pond, and the bottom is the habitat of crabs. Therefore, crab breeding must strictly control the content of hydrogen sulfide, requiring its content to be below 0.02mg/L. Second, the fertilizer water crab stocking requirements fertilizer water pond, in the breeding process to maintain a certain degree of fertility, must not lean water crab, which is very important to improve its yield and listing specifications, fertilizer water crab advantages are as follows: (1) fertilizer water can increase the number of benthos, through fertilizer water can also increase the natural bait of natural crab pond, so that crab everywhere can eat, eat full food, eat good food. (2) Fertilized water can promote the growth and reproduction of plankton, improve the ability of photosynthesis, provide enough dissolved oxygen for the water, promote the growth of Chinese mitten crab, especially increase the growth multiple after shelling. (3) Fertilizer water can promote the reproduction of plankton, effectively purify the water body, and reduce the content and harm of harmful substances. 1, fertilizer conditions (1) water quality light, transparency is too high to properly carry out fertilizer. Compound fertilizer, base fertilizer should be sufficient; inorganic fertilizer should be appropriate, and efforts should be made to promote the use of calcium dihydrogen phosphate. (2) After heavy rain, when the water quality turns white and turbid, it may be due to the influence of insects. It is recommended to kill insects first, then fertilize and adjust water. (3) When the vitality of the aquatic plants is not strong and yellow, it is recommended to use some fertilizer to strengthen the roots and protect the grass, so that the withered grass can regain its vitality and provide a better living place for the crabs. (4) topdressing should be flexible according to the water quality, follow the principle of "a small number of times". 2, it is difficult to analyze the reasons for fertilizer and water fertilization for many times, the reasons may be as follows: First, the amount of base fertilizer applied is not enough, and the nitrogen, phosphorus and other elements required for algae growth are not enough. The effective content of phosphorus in nitrogen and phosphorus elements is particularly important, while nitrogen content in water is relatively high, phosphorus in water is easy to be adsorbed and precipitated by other substances, resulting in imbalance of nitrogen and phosphorus content, so that the available nitrogen in water can not be fully utilized. At low temperature, the diatom content in the water body is particularly high, so in the low temperature season, the water temperature is lower than 15℃ to consider strengthening the application of available silicon. Other nutrients needed by phytoplankton are generally not scarce in water and can be ignored. It is recommended to use organic fertilizer as base fertilizer. Second, biochemical factors exceeded the standard. When the pH value is high (greater than 9), it is generally difficult to fertilize water. The bottom can be improved first, and then some acidic biological preparations can be used to adjust water and stabilize pH value; there are many kinds of zooplankton in the water body (rotifer, cladocera, siripod, etc.), so biological fertilizer preparation can be used after killing insects; there is much residual chlorine in the pond, so it can be neutralized with quicklime before using biological fertilizer preparation; when there are many residues of heavy metals, it is difficult to fertilize water, so detoxification can be used first, and then biological fertilizer preparation and fertilizer fertilizer can be used. Third, improper fertilization. The proportion of fertilizer is not appropriate, will lead to two situations, water quality too rich or not fat up. The correct fertilizer ratio is: N: P ratio is (3-4): 1. The order of fertilization is not reasonable will also lead to fat up. The correct sequence is to apply phosphorus fertilizer first and nitrogen fertilizer later. Quicklime should not be added after phosphorus application. Finally, the lack of algae species in the water body is also difficult to fertilize the water. 10-20cm of fresh water should be added first, and then biological fertilizer containing algae seeds should be used. If too many snails are put in at one time, they will eat too many microorganisms in the water and make the water thin. The snails can be put in batches. For the new pond mouth, first use base fertilizer, then use biological fertilizer containing algae seeds. Moss is a filamentous algae, its reproductive ability is very strong, harmful, when it reproduces in large quantities, it will absorb a lot of nutrients, making the water thin. When a large number of its death, the release of a large number of toxins, easy to cause hypoxia, causing harm to crab, so when the pond mouth moss should be dealt with in time. Some farmers used copper sulfate treatment, although the moss killed, but caused casualties of weeds and crabs, the loss outweighed the gain. At present, there is still no medicine on the whole market that can really kill moss without causing casualties of weeds and crabs. Some are only polymerized copper, chelated copper and other drugs, better than copper sulfate, but there are still large casualties for aquatic plants and crabs. The author's experience is: moss growth needs sunlight, and moss is living in the bottom of the water, can pass fertilizer water, increase the fertility of water, reduce transparency, reduce light. At the same time, apply the substance to the bottom, sink to the bottom, cover the surface of the moss, directly subtract its light, eliminate photosynthesis, and kill the moss while decomposing the corpse. Once two farmers each used 30 acres of pond mouth trial, the effect is good. Bloom "bloom" is a natural phenomenon in fresh water, caused by a large number of cyanobacteria bloom. Water blooms are usually blue or green. The main cause of "blooms" is eutrophication, and in Jiangsu Lake Taihu has become a headache for the government because of cyanobacterial blooms. Cyanobacteria bloom, secondary metabolism produces microcystins, crabs have toxic effects. After a large number of algae die, dissolved oxygen in the water is consumed in the process of decomposition, which makes the water seriously smelly. Dead algae also damage the liver through the food chain and have carcinogenic effects, which directly threaten human health. Cyanobacteria occurs in crab pond, and drugs such as chelated copper can be used to kill cyanobacteria first. After 3 hours, sodium thiosulfate is sprinkled for detoxification, and Bacillus is used at the same time. This method can effectively relieve cyanobacteria bloom, but pay attention not to hypoxia. Because of the high cost, general farmers, especially farmers with large water surfaces, cannot accept it. 5. Scientific feeding management Feed quality is the material guarantee for breeding big crabs and good crabs. In March, when the water temperature reaches above 10℃, the crab is fed bait. Food mainly includes animal carcasses and their carcasses, clam meat, snail meat, shrimp and wheat, grain, cakes, aquatic or terrestrial fresh grass. Feeding must adhere to the principle of fine, green and coarse reasonable mix. 4-5 Month, pond in the germination of aquatic plants, biological bait breeding, and just put crab species individual small, low water temperature, crab feeding intensity is not high, can feed less animal feed, more green, coarse feed. 6-10 In August and October, the individual of crab grows up gradually, the water temperature increases, the feeding intensity of crab is large, especially in August to October, the crab fattens and gathers yellow, the weight increases significantly, and more animal feed should be fed. Feed once a day around evening, feed thrown in shallow water pool, set up a multi-point food table. Each feeding amount accounts for about 10-20% of the crab's total weight, and it increases or decreases appropriately according to season, water temperature, weather, feeding and growth. In addition, in the actual operation should also pay attention to the following links: (1) Qingming time to put more than 300 kg per mu of fresh snails clams, etc., as the annual basis bait. (2)Feeding should be timed, positioned, qualitative and quantitative. (3)Artificial preparation of mixed feed, it is best to feed made into noodles or lump shape, such as conducive to eating crab shape. (4)In the early growth of crab mainly feed wheat, pumpkin, grain, cake, etc., in this period to promote feeding malt (malt feeding can ensure that it will not rot for 1-2 days), the rest of the feed should be cooked feeding. (5)The crab's life, to go through many times molt shell. Body enlargement, morphological changes, and limb regeneration occur after each molt. Molting runs through the whole growth and life process of crab. Therefore, molting hormone should be properly fed at ordinary times, and molting hormone feeding and feed feeding should be appropriately separated in time; in addition, during the molting period of river crab, fresh water should be frequently injected to maintain micro-flowing water, which can effectively stimulate river crab molting. (6)During the whole breeding cycle, it is necessary to sprinkle quicklime in an appropriate amount to purify the water quality on the one hand and increase the calcium content of the water body on the other hand, so as to prepare for repeated molting. Six, scientific conditioning water quality healthy crab on the quality of the water environment requirements are very high, must be scientifically conditioned water quality. Water quality indicators require transparency 35-40cm, dissolved oxygen above 5mg/L, pH 7.5-8.5, ammonia nitrogen concentration 0.2- 0.5 mg/L. The above water quality indicators can be detected clinically by means of water quality test kits, so as to take some measures (mainly simulating natural ecological environment) to regulate the water environment in a necessary, beneficial and timely manner. At the end of February and the beginning of March, the water depth is controlled at 0.6-0.8 m, from May to July at 0.8-1.0 m, and from August to October at 1.0-1.2 m. In spring and autumn, change the water once a week, deepening 30-40 cm each time. When changing water, drain and irrigate at the same time, and the temperature difference of water change shall not exceed ±5℃. If the bottom of the pool is more silted, the transparency is low, the water color becomes thick, the back of the crab is dark black, the abdomen is rusty, the foot ends become yellow, 7.5-15kg of fresh quicklime is used per mu, and the whole pool is splashed with water. It can be used continuously for 2-3 times, with an interval of 5-7 days each time. It can adjust the water quality, increase the concentration of calcium in the water, and is beneficial to the growth of the crab and the change of the color of the crab shell. At the same time, we should also pay attention to the following precautions: (1) to change water in time, the right amount of water to improve the environment, reduce the temperature. The suitable molting temperature of crab is 25-28℃. (2)Quicklime should not be used, reused and commonly used. If it is used frequently, the hardness of water will be too large, dissolved oxygen will decrease, and phosphate concentration will decrease. (3)In order to maintain a certain fertility of the pool water, it promotes the reproduction and growth of bait organisms such as snails and clams. (4)Mixed culture of crab and fish. Mixed culture of crab and fish can make full use of water space, improve bait utilization rate, purify water quality and effectively improve pond water quality conditions. But to raise crabs mainly, can be appropriate stocking a small amount of silver carp, bighead carp, grass, bream, tilapia, but not stocking carp, herring and other benthic carnivorous fish. Pay attention to escape. Crab market situation is not very stable, but as long as strengthen science and technology crab, improve variety quality, rational use of water, improve comprehensive benefits, adapt to market demand, market prospects are still very broad!