How to choose and buy high-quality crab seedlings: strong physique and strong crawling

Crab culture

Crab larvae, commonly known as "big-eyed larvae", are the fifth stage flea larvae that become big-eyed larvae after peeling. It has a pair of compound eyes attached to the end of the long eye stalk, exposed in the eye socket and got its name. Big-eyed larvae are the basis of breeding crabs and adult crabs, and their quality directly affects the survival rate of young crabs from Ⅱ to V, so we should pay attention to the selection and purchase of crab seedlings.

First, to understand the crab seedling cultivation process before choosing and purchasing crab seedlings, farmers should first understand the whole production process of the crab seedling farm, mainly including: parent crab, feed use, breeding cycle, and so on. Parent crabs used to reproduce crab seedlings are best derived from natural lakes and large water bodies, and male and female crabs should come from different waters to avoid inbreeding. Parent crab specification: female crab should not be less than 125g, male crab should not be less than 150g.

The quality of crab seedlings cultivated with harvest years (Artemia) is better, while the quality of crab seedlings cultivated with substitute diets such as freshwater fleas and egg yolks is poor.

In addition, the breeding period of crab seedlings is generally 19 days ~ 21 days, and the water temperature is about 21 ℃ at the time of emergence.

Second, do a good job in the quality identification of crab seedlings. 1. The body color of high-quality crab seedlings is yellowish, shiny and transparent, and there are no foreign bodies such as condensed worms or filamentous bacteria on the body surface under microscope. Low-quality crab seedlings, dark and light body color, milky white, orange red, microscopic examination of crab seedlings with bacteria, worm.

two。 High-quality crab seedlings have strong physique, uniform specifications, phototaxis, ferocious feeding and strong traceability. The crab seedlings crawl forcefully in the hand, and the response is agile when blown with the mouth. Grab a small amount of crab fry with your hand, shake off the water and shake it into a ball, which will disperse immediately after you release your hand. Low-quality crab seedlings, empty stomach, poor swimming ability, easy to move in the bottom of the water body, hand-grasped crab seedlings are easy to form a ball, not easy to spread.

3. Crab seedling specification normal crab seedling out-of-pool specification is suitable for 120000 ~ 140000 crab seedlings per kilogram, no more than 170000 at most. For the crab seedlings that reach this specification, there are fewer false seedlings, and it is more smooth to become young crabs. If the number of crab seedlings is too large, it means that the crab seedlings have a short age and soft carapace, which can not stand operation and transportation. If the number of crab seedlings is too small, the size of the crab seedlings is large, the shelling period is approaching, and the crab seedlings will die during transportation.

4. When the crab seedlings leave the pond, the salinity of the water body should not be higher than 4 ‰, the desalination time should not be less than 7 days old, the water temperature at emergence should be about 21 ℃, and the temperature difference between the seedling pond and the culture pond should be less than 2 ℃, no more than 4 ℃ at most.

Third, matters needing attention (1) the day before the crab seedlings leave the pond, it is best to disinfect them with medicine once, in order to kill some pests, reduce the occurrence of diseases during the culture period, and at the same time eliminate some crab seedlings with poor physique.

(2) when fishing crab seedlings, they should stop breathing and bait, and light trapping should be used, so that the crab seedlings have less impurities and strong vitality. Drain the water before packing and spread it evenly when entering the box to prevent crab seedlings from sticking to each other and causing death.

(3) early seedlings should be transported during the day and late seedlings at night, and sunscreen and wind protection should be used during transportation. Motor vehicle transportation, close the doors and windows when driving, open the doors and windows when parking, smoke is prohibited in the car, spray water every 2 hours on the way, increase the humidity of the crab seedling box.

(4) the crab seedling has been basically dehydrated after long-distance transportation. if it is directly put into the water, the Gill of crab seedling is easy to produce air bubbles and affect the survival rate. So there should be an adaptation process before the crab seedlings enter the pool: first, open the crab out of the box, sprinkle the crab seedlings with water for 5 minutes, soak the crab seedlings and the crab seedlings all in the pool water, then leave the water on the shore, repeat it again 15 minutes later, and finally slowly put the crab seedlings into the pool and raise them.