What are the criteria for selecting crab larvae? How to breed in spring and winter?

Spring and winter is a critical period for raising crabs, and the selection and release of crab seedlings determine the yield and benefits of year-end culture. During the release period of crab seedlings, crab farmers should carefully identify the quality of crab seedlings and carefully select high-quality crab seedlings for release. Crab fry is one of the key factors related to the high yield in the later stage, so what are the selection criteria for crab fry? How to raise crab seedlings in spring and winter?

I. selection criteria of crab fry

1. Select high-quality seedlings cultivated locally; crab seedlings cultivated in general soil ponds have stronger adaptability than those cultivated in factories; under the same conditions, crab seedlings cultivated in soil ponds should be selected first.

2. Select the crab seedlings with pure strain, strong body, uniform size, smooth body surface and agile activity; the seedlings are neat light yellow, translucent and translucent, with uniform distribution of melanin; do not choose unhealthy seedlings with condensed worms or foreign bodies on the body surface and appendages; do not choose young seedlings with translucent and whitish shells or old seedlings with dark black

3. the seedlings are over 6 days old, desalinated for more than 4 days, the salinity is reduced to about 3, maintained for more than 1 day, and the proportion of crab seedlings with uniform size is 80: 90%. Do not select young seedlings and flower-color seedlings that do not have enough desalination time, individuals are too small or uneven in size.

4. Put the crab seedlings pinched into a ball back into the water and swim away immediately without sinking to the bottom; if you put the seedlings with water in the palm of your hand, the seedlings can crawl with water without falling.

5. Grab a handful of crab seedlings by hand, and gently hold them with a sense of elasticity, sand and weight after throwing dry water; if you put them in your ear, you can hear an obvious rustling sound; if you hold them gently and then release them, they can quickly escape around, without agglomeration and mutual involvement, then they are healthy seedlings, otherwise they are inferior seedlings; 6. Observe the vitality and speed of crab seedlings swimming in the water; choose healthy seedlings that swim horizontally in the water, with fast speed, and crawl quickly after landing from the water. Do not choose shoddy seedlings that spin around in the water, lie on their back, move slowly or gather in a motionless mass.

7. Carefully observe the number of dead seedlings in the seedling pond. For example, if there are many dead seedlings in the pond, the survivors are also sick seedlings.

8. Crab seedlings have bait in their stomach, but not much. When crab seedlings are weighed, there are no residual bait impurities and dead seedlings, and the seedlings should be weighed after draining water in the cage.

Second, how to raise crab seedlings in spring and winter?

1. Sparse

General stocking (winter release) 120 million 160 crabs per kilogram 700 million 800 crabs / mu, no more than 900 / mu at most; if the crabs that have been shelled twice (spring release) are released through temporary culture, the amount of seeds per mu will be about 600. The winter stocking time is around the Spring Festival, the weather is sunny, and the temperature is 8: 10 ℃. If the conditions permit, it is better to put in when the water temperature reaches more than 8 ℃ after the beginning of spring.

2. Mixed culture

(1) principle: all fish that compete with the main culture object (river crab) for bait, or can eat the main culture object will not be mixed culture.

For example, herbivorous fish (grass carp, blunt snout bream), fish competing with crabs (common carp, herring), and aquatic animals that can eat river crabs (soft-shelled turtle, raw fish, etc.) are prohibited in crab ponds.

(2) all stocked fish should be beneficial to the growth of the main culture object.

For example: mixed culture of crab, warped-billed red mackerel, bighead carp and fine-scaled oblique jaw mackerel; mixed culture of crab, mandarin fish, bighead carp, bighead carp, green shrimp, crab, shrimp, yellow catfish (or Pelteobagrus fulvidraco), bighead carp and fine-scaled oblique jaw mackerel.

(3) the overgrown varieties should also have the following characteristics: there is a market, the product price is high, and it is easy to sell; it is beneficial to improve the environment of crab culture and improve the comprehensive benefit of crab pond.