Crab breeding technology requirements

The crab species undergoes several molting stages over about 10 days, eventually transforming into juvenile crabs. During this period, individual growth can vary significantly, with some reaching up to 50 grams while Others remain as small as 5 to 10 grams. Female crabs lack the long, rounded abdomen that is characteristic of mature females, and their gonads are not yet developed. Male crabs, on the other hand, have smaller chelae (claws) and immature reproductive organs. These early-stage crabs still have feeding value. However, if a female has a fully rounded, hairy abdomen and a male has large chelae with dense hair, it indicates they are mature and no longer suitable for consumption. In general, when selecting pro-crabs, choose those that are physically strong, have hard shells, appear plump, and weigh more than 100 grams. Crabs that are large and well-fed tend to produce more eggs after mating. When keeping crabs, it's important to maintain a higher ratio of females to males, ideally more females than males. It’s best to start keeping them before winter begins. Once selected, male and female crabs should be carefully housed in freshwater ponds. The breeding pond for parent crabs is typically oriented to the south, with a size depending on the number of crabs being raised—usually around 667 square meters. The water depth should be over one meter, with good bottom mud. Stocking density is generally between 250 to 500 kg per pond. To prevent escape, concrete walls at least 40 cm high should surround the pond, extending about 15 cm above the edge. Corners should be rounded to avoid sharp angles that crabs might use to climb out. The inlet and outlet should be equipped with nets to prevent crabs from escaping. To improve survival rates, earthworms can be placed on the ground or in the center, and aquatic plants should be planted at the bottom and around the edges to provide shelter. The stocking density should be kept at 1–2 crabs per square meter. Males and females should be kept separately to ensure proper selection before mating and to avoid interference. Before stocking, the pond should be disinfected with fresh lime. When the water temperature is above 10°C, feed the crabs every 2–3 days, increasing the frequency if the temperature rises. If the temperature drops below 8°C, reduce or stop feeding. Suitable feeds include small fish, silkworm pupae, quail meat, animal offal, grains, leeks, and similar items. Ensure the amount of food meets the crabs’ needs. To maintain clean water, flush the pond 2–4 times a month and ensure sufficient dissolved oxygen. If the water becomes too dirty, change it immediately. Daily inspections are essential to prevent escape. Inbreeding among pro-crabs significantly affects productivity, egg count, and larval development. Therefore, careful management during winter is crucial. To prepare artificial brackish water, select a clean source of fresh water, such as an uncontaminated reservoir or lake. Use sea salt rather than industrial salts. The preparation process involves crushing, dissolving, stirring, and sedimentation. After 1–2 days of settling, the water will become clear, with a transparency of about 1 meter and a pH between 7.5 and 8.5. At this point, the brackish water is ready for use. From December to early March, crabs enter their peak mating and spawning season. Mating usually occurs on land, as crabs prefer muddy or burrowed environments. Outdoor mating pools should be 0.5–0.6 meters deep, with an area of about 15 square meters. A bandit net is placed around the pool to monitor and observe embryonic development. Prevent escape by using bamboo barriers or brick walls. Mating is most effective when water temperatures range between 9–12°C, typically between February and March. Pro-crabs should be moved to the mating pool at this time. Too early or too late can negatively affect reproduction. Salinity stimuli trigger mating. Females are usually transferred 7–15 days before spawning, achieving an ovulation rate of over 95%. A 3:1 or 2:1 male-to-female ratio is ideal. After about 15 days, most females will spawn. To avoid aggression, males should be removed once spawning is complete. During incubation, strict control of water quality is essential. Sudden changes in salinity or temperature can lead to embryo loss or death. For juvenile crab quality assessment: 1. **Color**: Young crabs that have not been out of water for long are preferable. If they are too dry, their carapace turns pale yellow. 2. **Activity**: At temperatures above 4°C, active movement indicates good health. If low, crabs may become dormant. Warming them slightly should revive them quickly. When fertilized eggs become transparent, larvae are about to hatch. They should then be moved to indoor nursery ponds. Water conditions must be controlled: dissolved oxygen above 5 mg/L, temperature between 18–25°C, and shallow water (10–30 cm). Maintaining a gentle flow helps larvae move. Avoid strong light, which can cause localized mortality. Monitor nitrogen levels, especially nitrites, which are harmful to larvae. Also, prevent excessive algae growth. Feeding depends on the larval stage. Early zoea stages require planktonic algae and Artemia nauplii. As they grow, they need more Artemia. Starvation can lead to cannibalism. Proper bait palatability is critical for survival. The zoea undergo five molts over about a month, becoming "crab larvae" capable of living in freshwater. Green algae and diatoms like *Platymonas*, *Dunaliella*, and *Phaeodactylum* are commonly used. Rotifers and Artemia are also beneficial for early-stage crabs due to their fast growth and adaptability.

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