River Crab Farming Spring crab stocking is the beginning of the annual breeding season of river crabs, and whether it is successful or not directly affects the harvest at the end of the year.
The spring river crab stocking management technology includes pond disinfection, aquatic weed planting, crab seed selection and stocking, fertilizer hydroponic algae, water quality control, bait feeding, daily management and other aspects, among which, pond disinfection, crab species selection and stocking, fertilizer hydroponic algae are the three most important points affecting the early survival rate and molting growth.
1. Disinfection of the pond.
Pond disinfection is the first step in adult crab farming. Before disinfection, the pond water should be drained, the pond should be fully dried, and the bottom of the pond should be dried and cracked, so that the organic matter in the sediment can be fully oxidized and decomposed, and the redox potential of the sediment should be increased. Quicklime or bleaching powder is used for disinfection, quicklime can be used 100 kilograms, bleaching powder can be used 50 kilograms, and the whole pond is splashed after the water is turned into water to kill predator organisms, and calcium and magnesium elements are supplemented at the same time. Pyrethroid drugs can be enriched in the sediment and have a long half-life, resulting in chronic poisoning of shrimp and crabs, resulting in river crabs not eating, hepatopancreatic degeneration, and eventually leading to "water deflated disease" (hepatopancreatic necrosis syndrome).
2. Selection and stocking of crab species.
In recent years, with the continuous improvement of crab breeding technology, the yield per mu of most crab breeding farms has reached more than 250 kilograms. However, while the yield per mu increased, the quality of crab fingerlings decreased to a certain extent, which was one of the reasons for the low recapture rate of adult crab breeding. How to do a good job in the selection of crab species, it is necessary to carefully sample and check the body surface, gills, hepatopancreas and other three aspects of crab species. High-quality crab species need to have good genetic advantages, smooth and clean body surface, and no parasites; The chela and footsteps are sound, and the claw tips are not worn; The gills are bright and neat, and there are no lesions and fractures; The hepatopancreas is plump and orange-yellow; The period of temporary recuperation should not exceed 1 day.
The stocking density of crab fingerlings is adjusted according to the breeding mode, and the stocking density of large-scale high-quality adult crab breeding mode is generally 1200-1500 mu, and the size of crab fingerlings is about 50 catties; The stocking density of high-yield, medium-sized adult crab breeding mode is generally 2000-3000 mu, and the crab seed size is about 80 catties.
When the crab fingerlings are stocked, the crab fingerlings are placed on the floating board, so that the crab fingerlings can climb into the water freely, and at the same time, the floating plate is rowed at a uniform speed in various places in the pond, so that the crab fingerlings are evenly distributed in the pond to avoid aggregation.
After the crab fingerlings are stocked, disinfect the pool water with disinfectants such as iodine, and feed the bait in an appropriate amount according to the temperature.
3. Fertilizer hydroponic algae.
In spring, when the temperature is low and the number of planktonic algae is low and the vitality is weak, suitable fertilizers should be applied on sunny days to supplement algae species (exogenous water or commercial algae species) to promote algae growth. More abundant algae have a variety of benefits, such as reducing water clarity, inhibiting moss growth, and stabilizing pond water quality. When fertilizing water, follow the principle of small amount and multiple times to avoid excessive fertilizer at one time, which will lead to local deterioration of water quality and affect the molting of crab species. Regularly check the transparency and water quality indicators of the water body, and replenish fertilizer in time. After fertilizing the pond, the water body is fertile, lively, tender and refreshing, the aquatic plants are faintly visible, the transparency is about 50cm, and the ammonia nitrogen and nitrite are controlled at a low level.
The study found that juvenile and adult crabs have the same ability as flea-like larvae and big-eyed larvae - filter feeding, digest and absorb the planktonic algae in the water body, and provide abundant natural bait for crab species in early spring through fertilizing hydroponic algae, promote early feeding and supplement nutrition of river crabs, and ensure the smooth molting and growth of crab species.