In recent years, with the development of crab breeding, people's demand for river crab is getting higher and higher. People all hope to eat crabs that are “bigâ€, “clear†and “fullâ€. But at present, individuals are small and lean, body color is blue and black, and poor quality shell crabs are flooded with the market. The number of clear-water white hairy crabs and abundant lipid-rich hairy crabs is not much. Therefore, in order to satisfy people's pursuit of high-quality crabs, we must improve farming techniques and raise large-scale, high-quality crabs. However, in the process of breeding large-scale commercial crabs, problems such as precocious puberty, river crabs, and long-term problems such as "fat crabs" and "lazy crabs" are often encountered. The key technology for breeding large-size crabs is how to solve these problems. The New World Bioengineering Development Center in Jiangsu Province, after years of experiments, has mastered the technology of breeding large-size commercial crabs. The measures taken are mainly the following: First, to prevent crabs, precocious puberty, large-eyed larvae to develop crabs, crabs, crab crabs often occur in the process of premature sexual problems. Precocious crabs often cause the crabs to grow small and become “stingy crabsâ€. This type of crab meat has bad taste and low prices in the market, often affecting the overall benefits of crab farming. The main cause of precocious crabs is poor quality of crab seedlings, excessive feeding, and poor water quality. The solution is as follows: 1. Select high quality seedlings The germplasm resources of Eriocheir sinensis are divided into three water systems according to geographical distribution, namely, Yangtze River, Liaohe, and Minjiang rivers. Among the three types of crabs, the Chinese mitten crabs in the Yangtze River water system have the largest specifications and the best quality, and are well received by the market. The meat quality of the Liaohe River and the Minjiang River is much lower than that of the Yangtze River Crab. However, at present, the source of the crabs in the Yangtze River has been severely declining. The main cause is human-induced damages. For example, fishermen in the Yangtze River in winter not only do not protect the crabs in the sea, but also catch eggs and crabs in the Yangtze River Estuary. In addition, due to the lack of crab breeding techniques along the rivers along the river, some first-year-old crab species are precocious. These growing “small green crabs†lay their eggs and severely affected the Yangtze River crab germplasm. Due to the decline of the Yangtze River Crab and the drive of economic interests, the crabs of the Liao Crab drove in and out, mixing the fish, resulting in the germplasm of the Yangtze River Crab. Due to severe damage to the natural resources of crab seedlings, most of the crab seedlings are now artificially propagated. However, due to the lack of technology in some nursery households during artificial breeding, one-sided pursuit of efficiency, adoption of intensive culture, stable water quality, and ample diets have created a good living environment for seedlings, especially for some foods containing antibiotics and certain tropins. Some seedlings develop too early and the rate of precocious puberty after ponds is relatively high, generally about 20%; the highest is 45%. In some nursery sites, natural baits and plant foods are mixed and fed, and the rate of precociousness of young seedlings is at most 10 to 15%. Therefore, when buying crabs, you should go to a reliable company with higher seeding techniques to select the seed. 2. Controlling the amount of juvenile precocious puberty The juvenile precocious puberty not only has a great relationship with the nutrition of the crab, but also has a certain relationship with the quality of the bait and the ratio of the animal and vegetable bait. Because there are few bait in the natural world, the juvenile crabs need to carry on the bait foraging in order to consume more energy, so the growth is relatively slow. Under artificial conditions, the bait is abundant and nutritious, which promotes the growth of the crab. Therefore, from the time of the big eye larvae to the young crab before and after the v period, it is possible to add some floating plants to the pond to control the intake of nutrients without feeding the bait. After the feeding period, the juvenile crabs should be fed mainly with plant foods, and the animal foods should be attached. The feeding amount of the bait should be controlled so that the crabs gradually transition from semi-saturated state to feeding. In order to prevent juvenile crabs from developing prematurely and cause precocious puberty, special attention should be paid to the fact that the bait used in the market must not contain any feed supplemented with hormones, and the requirements for plant proteins should be high in the early feeds, and the animal protein requirements in the post-fattening period must be high. high. 3, control the density of the placement of small density will increase the unit of water each crab has, the increase in the possession of the bait, this comfortable environment is also easy to make crab precocious. To put artificial large-eyed larvae seedlings, the density should be controlled at about 0.8 to 1.0 kilograms per acre pond, which can reduce the rate of sexual precocity by nearly 10%. 4, pay attention to the quality of water temperature crab crab breeding should pay attention to the frequent detection of water temperature. Water quality Water temperature also has a greater relationship with the occurrence of controlled precocious puberty. The pH of the water should be controlled within 7.5-8.5, and the salinity should be kept below 4‰. Excessive water quality can also lead to gonadal development and cause precocious puberty. If the water temperature is too high, crabs will be precocious. In order to control the water temperature, the water level should be kept at the shallowest point of 75cm, and the deepest point should be 120cm. The vegetation around the pond should be abundance from July to August so as to avoid accelerated metabolism and rapid development of juvenile crab due to elevated water temperature. Second, reduce the crab burrowing crabs like to dig caves, burrowing crab is a way to adapt to the enemy, but also can reduce the fighting with each other, is conducive to the safe growth of crabs. However, river crabs play a detrimental role in river crab breeding. For instance, river crabs playing in caves can cause difficulties for fish farmers and cause some “lazy crabsâ€. "Lazy Crab" is a result of the crab's long-term escaping into the hole, not going out for food, and having a low temperature in the hole and growing slowly. Therefore, the growth of these crabs is extremely poor, and their size is also less than that of unoccupied ones. Therefore, it is necessary to reduce the burrowing of river crabs for the cultivation of large-size commercial crabs. According to long-term observations, the crabs in caves where the breeding density is high, the concealed objects in the water, and the supplies for climbing are less, the water temperature is too low, the enemies are excessive, the water quality is poor, and the conditions are poor are more serious. This shows that river crabs are adapted to harsh environments. Therefore, in order to reduce the phenomenon of crab burrowing, we must create a good ecological environment. To create a good ecological environment, we must do the following: (1) Crab ponds should be quiet, sheltered from the sun, have plenty of water, and have a suitable water temperature. (2) The water quality should be kept fresh, and the transparency should be 30-40 cm. There should be no pollution. Regularly measure the amount of dissolved oxygen, ammonia nitrogen, and pH, and if not, take immediate action. (3) The crab pond consists of a deep water zone, a shallow water zone, and a grassy shore. The water is implanted with an appropriate amount of submerged, emergent, and floating aquatic plants to provide a good environment for crabs to eat and inhabit. (4) Pay attention to the rich bait, complete nutrition, green, coarse and fine bait. In order to reduce the crab hole phenomenon, in addition to improving the breeding ecological environment, we should also strengthen the usual management. Such as feeding should pay attention to crab food intake, found that reduced food intake, burrowing increase measures should be taken in time to attract crabs out of the hole or the crab dug out to focus on feeding, to change their habits, increase food intake, in order to achieve aquaculture Specifications merchandise crab purpose. Third, control the number of feeding bait crab breeding has a higher demand for feeding, feeding the good or bad is the key to whether or not to develop large-size commodity crab. Therefore, in order to effectively control the crab size in the crab raising process, one should pay attention to the feeding technique and pursue the quality of feeding, especially the ratio of animal and vegetable protein and the content of crude fat should be strictly controlled. Due to the eating habits of crabs, the crab diet must not break. The New World Bioengineering Development Center of Jiangsu Province adopts advanced biological science and technology (without using adhesives) and uses computer formulas to make a biological pellet feed. This biological bait not only solves the problem of non-breaking, but also has the advantages of comprehensive nutrition, better amino acid balance, special benefits in absorption, promotion of growth, and enhancement of disease resistance. In the Xinghua Aquatic Company Crab Breeding Breeding Center, a relatively clear result was achieved. Due to reasonable ratio of this kind of food, the content of crude fat is controlled within 3% to 4%, so 75% of the large-eyed larvae of one year reach more than 150 grams. The quality of feeding should be based on the water temperature and the stage of growth of the crab. Under normal circumstances, feed can be fed at 3-5% of the amount. When the water temperature is too high or too low, the feeding amount can be appropriately reduced. During the period from June to August, the crabs are in a suitable growth stage, and they can adopt the biogranule bait formulation in the pre-harvest period, and use the pellets for the dieting of fat after 9-10 months. In the crab breeding process, intensive culture should be adopted, especially in the later period to increase the proportion of animal food in the bait, pay attention to nutrition, to meet the needs of crab growth, promote the growth of the crab shell, so as to achieve the desired commodity crab specification. Of course, the problems encountered in the cultivation of large-size commodity crabs are not merely these. There are still many problems that need to be studied and explored. However, as long as the solutions to these problems are mastered, large-scale and high-quality commercial crabs can be cultivated.
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