Technical Points and Methods for Rice-Field River Crab Farming Explained

As crab farming develops faster, farmers are also constantly exploring new techniques for farming crabs, so rice-field river crab farming has thus appeared in the public eye, and also provides a better method for crab farming.

Rice-field river crab farming technology

1. Preparation of crab-farming rice fields

Crab-farming rice fields need anti-escape facilities. The field ridges should be 60 cm high and 40-50 cm wide, and covering the ridges with double-layer plastic film is sufficient. Smooth asbestos tiles or polyethylene mesh can also be set up around the rice field to prevent escape. The water inlet and outlet should also be fitted with anti-escape screens. Dig a ring ditch 3 m from the field ridge; for raising crab larvae and crab seed, a ring ditch 1 m wide and 0.8 m deep is sufficient. For raising adult crabs, the ring ditch should be 2-3 m wide and 1 m deep. Ditches and pits (crab ponds) should also be dug in the middle of the field. The ditches should be 50-60 cm wide and 50 cm deep; for raising adult crabs they can be widened to 1 m and 60 cm deep. The pits should have an area of 8-10 sq m and a depth of 1 m. The ditches and pits account for about 30% of the total rice-field area. Crab-farming fields are best arranged as farming units of 2-3 mu each.

2. Stocking of seedlings and seed stock

For rearing crab seed, stock 0.5 kg of crab larvae per mu. For farming adult crabs, about 1500-2000 crab seed with an individual weight of 10-15 g can be stocked per mu. Early-bred crab larvae of the same year can also be used, placed in a greenhouse for intensive rearing, and then released into the rice field in May, which can shorten the farming cycle.

3. Feeding and management of crabs

Feed 1-2 times a day, generally at 8-9 am and 4-5 pm. Especially when farming adult crabs, feeding in the evening should be the main feeding, with a daily feeding rate of 3%-5%. Feeding points should be on pre-set feeding platforms or on the banks on both sides of the crab ditch. When feeding, pay attention to checking whether the field ridges have holes; because river crabs have a burrowing habit, holes should be plugged promptly when found. During heavy rain, pay attention to preventing waterlogging and crab escape; in dry seasons, pay attention to water shortage. Under normal conditions, keep the water depth in the rice field at 6-10 cm. To keep the water quality fresh, change the water frequently: in June-July, change water once a week; in August-September, change water 2-3 times a week; after September, change water once every 5-10 days. Each water change should replace 1/3-1/5 of the water. In addition, during the rearing period, apply quicklime once every 10 days in the ditches and pits to make the water reach 5-10 mg/L.

Economic benefits of rice-field river crabs

Raising crabs in rice fields is a highly profitable fishery-farming integrated production model. Dense clusters of rice plants not only form places for crabs to hide and molt, but are also an excellent living and habitat environment for them. Not only can crab larvae be stocked, but juvenile crabs can be raised into crab seed, and adult crabs can also be farmed. In 1996, in Shuyang County, Jiangsu Province, rice-field adult crab farming had already reached a production level of 500 kg of rice per mu and 30 kg of crabs, with an income of about 5000 yuan per mu, which is 2-4 times the income of conventional rice.

Farming conditions for rice-field river crabs

The rice-field area for crab farming should be 2-20 mu. Fields should be selected with fresh water quality, water sources and bottom soil free of industrial pollution, convenient water inlet and drainage, and sufficient sunlight. The bottom soil should preferably be clay loam, non-seeping and non-leaking; the field ridges should be 0.8-1 m high, with a slope of 1:2 or 1:2.5, and should be compacted to strictly prevent gaps from remaining in the ridges, which could cause water leakage or crab escape.

Dig a ring ditch around the inner side of the field ridge, 2-3 m wide and 0.6-0.8 m deep, as the main place for crab farming. Field ditches should be dug well, in the form of a “cross” ditch or a “well” ditch, for crabs to crawl into the rice field to feed and hide. The dug ditches should be about 0.5 m wide and 0.5 m deep, and connected with the ring ditch.

Usually, a temporary holding pond of sufficient area is dug at one end or one side of the field to rear megalopa or temporarily hold crab seed; it can also be used when harvesting adult crabs. Its area accounts for about 5% of the field, with a depth of 1 m. The total excavated area for crab farming can generally account for 10%-15% of the total rice-field area.

For anti-escape facilities, plastic boards or double-layer agricultural plastic film anti-escape walls can be set up around the crab-farming rice field, usually 50-60 cm high, buried 10-15 cm into the soil, and fixed with wooden stakes. The anti-escape wall should incline inward at an angle of 20-30 degrees. The water inlet and drainage gates should allow free irrigation and drainage, with water level easy to control and safe and reliable. The gates should be sealed with silk cloth to prevent crabs from escaping or harmful organisms from entering.

For rice variety selection, choose varieties with strong fertilizer tolerance, hard stems, lodging resistance, a long growth period, and high yield. Varieties that do not require sun-drying of the field should be given priority when selecting rice. If the field needs to be sun-dried during river crab farming, the principle should be multiple short periods; when sun-drying, lower the water level until the rice-field surface is exposed above the water.

Technical points for rice-field river crabs

1. Rice planting pattern: large-ridge double-row, changing the conventional 9-cun single ridge to two ridges spaced 6 cun and 12 cun apart for transplanting.

2. Field engineering: temporary holding pond 10 m x 25 m x 1.0 m; ring ditch trapezoidal, with a top opening of 1.2 m, bottom width of 0.6 m, and depth of 0.5 m.

3. Stocking size and density: stock about 500 juvenile crabs per mu at 70-80 crabs per jin.

4. Stocking time: in late April each year, cultivate a small amount of Elodea in the ring ditch, release overwintered juvenile crabs into the temporary holding pond disinfected with quicklime, observe and feed fine feed on time and in the right amount, and release them into the main field promptly 15-20 days after transplanting.

5. Plant non-GMO soybeans on the ridge at a plant spacing of 7 cun.

6. Daily management

(1) Water quality regulation: after each molting of river crabs, apply quicklime at 5 kg per mu; 48 hours later, splash activated photosynthetic bacteria at 0.6-0.8 kg per mu; deepen the water layer as much as rice allows.

(2) Feed feeding: from releasing juvenile crabs in the temporary holding pond to early July, feed mainly high-quality complete feed and small fish and shrimp; from mid-July to mid-August, feed mainly green feed, together with small fish, shrimp, field snails, river mussels, etc.; after mid-August, switch to mainly high-protein fine feed, paired with new corn, new sorghum, etc.

(3) Scientific fertilization: before rotary tillage in crab-farming rice fields, apply 100 kg of organic fertilizer per mu; for green-turning fertilizer and topdressing, use less and apply frequently, with each fertilization amount not exceeding 3 kg per mu.

(4) Disease prevention and control: before stocking juvenile crabs, disinfect with quicklime (70 kg per mu) with 10 cm of water; for the purpose of calcium supplementation, splash 20 kg of quicklime per mu in the main field. Before juvenile crabs enter the pond, disinfect them with a 3% salt water or potassium permanganate solution bath.

(5) At each stage of farming, monitor water ammonia nitrogen value, dissolved oxygen content, pH value, and nitrite on time, and take measures such as changing water to regulate the numerical range suitable for rice growth and river crab growth and molting.

Because rice-field river crab technology has been vigorously promoted, the efficiency of crab farming has also been greatly improved, which has also promoted the rapid development of the domestic crab market, and the crab market has been improving all the way.