First, choose the crab species cultivated by the Yangtze River seedlings. At present, China's cultivated crabs mainly come from the Yangtze River, Liaohe and Lancang three major water systems. The crabs in the Yangtze River water system are referred to as the Yangtze River crabs. The crab shells are light yellow, oval, and sharp, with the fourth side teeth prominent and the central depression of the frontal teeth apparent; the second foot is equal to the third foot and the fourth side tooth is long. The ratio of the footpath to the third foot is 1:20. The footsteps are golden yellow, and the second foot and the third foot have no bristles. The crabs of Yangtze River grow fastest and have the largest individuals. The crabs of other river systems can only exert their regional growth advantages under the environmental conditions of their own water systems. When purchasing crab species, it is necessary to understand the source of crab seedlings and require that the pro-crabs come from the Yangtze River water system. Individuals are relatively large. The female crab weighs only 100 grams and the male crab weighs only 150 grams or more. It's best to purchase earth crabs to simulate large-eyed larval reared crab species that reproduce in natural environments.
Second, remove precocious crab species. Precocious crabs are crabs in the breeding process, due to accumulated temperature, nutrition and other causes of small individuals, but the gonads have developed mature crab species. The identification method is: A look at the crab umbilical: precocious female crabs have long hairs around the umbilicus, and the male crocodile within the plastron has developed into a white, hard, osteogenic tube. Second, to see the villi: precocious crab species chewing feet or step foot villi thick and long, darker color. 3. Look at the color of the breastplate and the crab pattern: The precocious crab species has a dark green or blue back, and the back is uneven. Four look at the gonad development of crab species: If there are two purple strips on the liver, even eggs, it is a sexually mature ovary; there are two white strips, it is a mature testis. Precocious crab species in crab breeding, the vast majority due to difficulties in oyster shell death, so when buying crab species to be identified and removed.
Third, pay attention to the transport and disinfection of crab species. The shorter the time for transportation of crabs is, the better. It is better that within 12 hours, the crabs are planted in bale bags, dense mesh bags or crab seed boxes, and they are prevented from being squeezed and dehydrated during transportation. The crabs that are transported should be soaked in water for 2-3 minutes before they are stocked. This is repeated 2-3 times to allow the crabs to suck enough water. In order to prevent the crab species from bringing in parasites and germs, they should be immersed and sterilized for 3-5 minutes after being immersed in water and then allowed to climb into the aquaculture waters. Commonly used drugs include 2-5% saline solution, 10 -15 mg/L formalin solution, 2-4 mg/L bleach solution, 15-20 mg/elevated potassium manganate solution, 8-10 mg/L copper sulfate solution, 15-20 mg/L zinc sulfate Solution, 2-4 mg/l terramycin solution.
Fourth, to grasp the time and density of crab species. The stocking of crabs is suitable from the end of February to the beginning of March when the water temperature is 8-12°C. The crab species has a size of 100-200 pieces per kilogram, generally 300-500 pieces per acre, and no more than 600 pieces. At the same time, it is necessary to raise the animals after they are raised. Holding is the transitional stage before the stocking of crabs. The stocking of the crabs after the temporary raising can greatly increase the survival rate of the lower ponds. The length of the temporary maintenance period is determined by the water temperature and the growth of aquatic plants in the pond.
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