Rice field finishing is a critical step in setting up an effective environment for crab farming. The selected paddy fields should be easily accessible for feeding and fortification, with high and wide field ridges to prevent crabs from escaping. Typically, the ridges should be raised 50–60 cm high, with a top width of 50–60 cm. In the center of the field, "well" or "tian" type ditches are dug, with a standard depth of 30 cm and a width of 40–60 cm. A small pit measuring 6–8 square meters, about 60 cm deep, is also constructed to provide shelter for crabs during their juvenile stage. Drainage ditches are placed in opposite corners of the field, ideally using pipes. The inner end of the pipe should be covered with a double-layer net to prevent young crabs from escaping, as well as to keep out predators like frogs and voles. Before introducing crabs, anti-escape walls should be installed. Two common methods include embedding a glass fiber fence on the inner side of the ridge, which should be 60 cm tall with 40 cm remaining above ground, or using bamboo poles and plastic sheets to create a sloped barrier that leans inward at 30 degrees and has semi-circular corners. Additionally, some hidden structures can be added within the field to reduce predation and improve survival rates.
Feed management plays a key role in ensuring healthy crab growth. Early-stage feed includes fresh water grass, fish gills, shrimp stomachs, cooked pig blood, tofu, and similar items. As the crabs grow, additional food sources such as snail meat, cooked pork, soybean residue, crushed rapeseed cake, soybean cake, cooked corn, wheat, pumpkin, and restaurant waste can be introduced. During the early stages, food should be filtered through gauze and fed 3–4 times daily, with portions amounting to 30–50% of the total crab biomass. Later, feeding is done once per day, preferably in the evening, to align with crabs' nocturnal feeding habits. The feeding amount is typically 5–8% of the total weight of the seedlings, and this can vary based on factors like water quality, temperature, and molting cycles. It's important to ensure that crabs are well-fed but not overfed.
Water quality management is essential for maintaining a healthy ecosystem. When releasing crabs into the rice field, fresh water is added to a depth of 10 cm, gradually increasing as temperatures rise and crabs grow. The water level should stabilize between 15–20 cm. Water is changed weekly, with each change involving 5–10 cm of new water to maintain freshness and oxygen levels. Lime is applied monthly at a rate of 20 kg per acre to make the water slightly alkaline, which helps in disinfection and calcium supplementation. Based on water conditions, organic manure (100–130 kg/acre) or urea (5–7 kg/acre) can be used to further enhance water quality. If possible, maintaining a slight flow of water in the field can stimulate appetite and promote shell development.
Disease prevention and control are crucial to avoid losses. Young crabs are vulnerable to predators such as waterflies and mice, which can cause significant damage. Mice, in particular, can kill 20–30 crabs overnight, so rodent control measures such as traps and manual removal are necessary. Aquatic plants should be soaked in lime water (20–30 g/m³) before being planted, and regular treatments with quicklime help disinfect the water and prevent disease outbreaks. When applying pesticides, it's important to use high-efficiency, low-toxicity, and low-residue options, applying them in small doses to minimize contamination. After pesticide application, water should be changed to ensure it is safe. Juveniles are usually harvested before the rice harvest in mid to late September.
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