1, Crab quality identification of high-quality crab seedlings: body color was pale yellow, shiny and transparent sense, microscopic examination of the surface without polymicrons or filamentous bacteria and other foreign bodies, individual crabs stout, containing 130,000 per kilogram Large-eyed larvae. Inferior crabs: poor or contaminated body, body color is milky white, black or orange (commonly known as variegated seedlings), dullness, and the proportion of yellowish crabs is less than 15%. The quality of the variegated seedlings is poor, and in the nursery pond, there are mostly no foods in the stomach and the individuals are small. The black seedlings are different from the crab seedlings that are close to the metamorphosis of the molt, and their body color is a sick melanin agglutination reaction. The whitish white crab seedlings have a lot of Vibrio or Bacillus microscopically in their bodies, and their body surface is clean. Only a few individuals have a small amount of poly-deuteroids and filamentous bacteria. The stomach and intestines often have no food. In the same nursery pool, the individual size of the crab seedlings can be seen to be uneven, and the individuals as a whole are small, with 150,000 crabs per kilogram or even more. There is also a kind of crab seedling whose appearance is similar to that of high-quality crab seedlings, but the body surface contains attachments such as filamentous bacteria or polypule. 2, Crab selection techniques selection of high-quality crab is the first condition to improve crab big eye larvae to secondary metamorphosis survival rate. In addition to the normal appearance of high-quality crab (phototaxis, strong retrogression, fierce feeding, crawling quickly after leaving the water, pushing a hand and feel, immediately spread out after loosening), 1 body yellow with blue, transparent carapace, Gastrointestinal full, appendages intact; 2 Microscopic examination of the body surface without poly-insects or filamentous bacteria and other foreign matter; 3 Large-eyed larvae not less than 6 days old, has been able to adhere to the rope, the salinity out of the pool generally does not exceed 7 ‰; 4 The proportion of whiteheads with white whitishness does not exceed 10%. Inferior seedlings mainly manifest as: 1 body color black and white mixed, or white, small individuals, empty stomach without food; 2 stomach whitening "white head" ratio is too high; 3 seedling body color is normal, but the body has a filamentous Bacteria and other foreign substances; 4 Crab seedlings with excessive medication during the seedling raising process have poor immunity and are prone to emergency reactions due to sudden changes in environmental conditions, resulting in infections or complications leading to a large number of dead seedlings; there are a large number of dead in the pool. The phenomenon of seedlings; 6 large eye larvae less than 6 days of age, desalination time less than 4 days, desalination of salinity more than 10 ‰. There is also a kind of crab seedlings with surface attached to filamentous bacteria, polypods and other attached organisms. It is better to use a drug to disinfect the big eye larvae one day before disinfection to kill some pests and reduce the occurrence of diseases during the breeding period. Can eliminate some of the poorer crabs. And the use of stop lights to lure and catch crab seedlings, less crab impurities, strong vitality. Before loading, the water should be drained basically and the crabs should be loosened when they are put into the box to prevent the crabs from sticking to each other and causing death. Crabs that need long-distance transportation should purchase tender tender crabs. It is better to use 6-7 days old big eye larvae, and it should not be too old. Otherwise, it will die during metamorphosis due to molting, especially during the later period of day. This is especially true of the high stage.
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