Crab Seedling Selection Standards and Spring and Winter Breeding Methods

Spring and winter are critical periods for crab farming; the selection and stocking of crab seedlings determine the annual yield and profitability of the farming operation. During the crab seedling stocking period, crab farmers should carefully assess the quality of the crab seedlings and hand-pick high-quality seedlings for stocking. Crab seedlings are one of the key factors determining whether there will be a bumper harvest later on. So what are the standards for selecting crab seedlings? How should crab seedlings be bred in spring and winter?

I. Standards for selecting crab seedlings

1. Choose high-quality seedlings bred locally; generally, crab seedlings bred in earthen ponds have stronger adaptability than those bred in factory-based systems; under equal conditions, choose crab seedlings bred in earthen ponds first;

2. Choose crab seedlings with pure strain, robust bodies, uniform size, smooth and clean body surfaces, and agile movement; the seedlings should be uniformly pale yellow, crystal clear and translucent, with evenly distributed melanin; do not choose unhealthy seedlings with Zoothamnium on the body surface and appendages or with foreign matter attached; do not choose tender seedlings with semi-transparent, whitish shells or old seedlings that are deep black;

3. Crab seedlings that are more than 6 days old, have been desalinated for more than 4 days, with salinity reduced to about 3 and maintained for more than 1 day, and with a uniform size proportion reaching 80-90%; do not choose tender seedlings and mottled seedlings that have not been desalinated long enough, are too small, or are uneven in size;

4. Put a handful of crab seedlings squeezed into a ball back into the water; they should immediately scatter and swim away rather than clump together and sink to the bottom; place seedlings together with water in the palm of your hand; the seedlings should be able to crawl while carrying water without falling off;

5. Grab a handful of crab seedlings, shake off the water, and lightly hold them; they should feel elastic, gritty, and heavy; hold them near your ear and you should hear a distinct rustling sound; hold them lightly and then release, and they should quickly scatter in all directions without clumping or tangling with one another, which indicates healthy seedlings; otherwise they are poor-quality seedlings; 6. Observe the vitality and speed of crab seedlings swimming in the water; choose healthy seedlings that swim horizontally in the water at high speed and crawl rapidly after leaving the water and coming ashore; do not choose poor-quality seedlings that spin in the water, lie on their backs at the bottom, move slowly, or gather in a clump without moving;

7. Carefully observe the number of dead seedlings in the seedling pond; if there are many dead seedlings in the pond, the surviving ones are also diseased seedlings;

8. The crab seedlings should have food in their stomachs, but not much; when weighing the crab seedlings, there should be no residual bait, impurities, or dead seedlings; the seedlings should be weighed after draining water in a net cage.

II. How should crab seedlings be bred in spring and winter?

1. Stock at low density

Generally, stock 700-800 crab juveniles per mu of 120-160 individuals per kg (winter stocking), with a maximum of no more than 900 individuals per mu; if through temporary holding, stock crab juveniles that have molted 1-2 times (spring stocking), then the stocking amount per mu is about 600 individuals. The winter stocking time is around the Spring Festival, on clear days, with a temperature of 8-10 degrees C. If conditions permit, it is better to stock after the beginning of spring when the water temperature reaches above 8 degrees C.

2. Mixed culture

(1) Principle: Any fish that competes for feed with the main culture target (river crab) or that can prey on the main culture target must not be mixed in.

For example: herbivorous fish (grass carp, blunt snout bream) are prohibited in crab ponds, as are fish that compete with crabs for food (common carp, black carp), and aquatic animals that can prey on river crabs (soft-shelled turtles, snakehead, etc.).

(2) Any secondary fish stocked should be beneficial to the growth of the main culture target.

For example: mixed culture of crabs, topmouth culter, bighead carp, and Xenocypris microlepis; mixed culture of crabs, mandarin fish, bighead carp, Xenocypris microlepis, and oriental river prawn; mixed culture of crabs, oriental river prawn, Jianghuai yellow catfish (or yellow catfish), bighead carp, and Xenocypris microlepis.

(3) The secondary culture species should also have the following characteristics: there is a market for them, their product prices are relatively high, and they are easy to sell; they help improve the crab farming environment; they help increase the overall benefits of the crab pond.