What conditions are needed for raising crabs in rice paddies?

The rice paddy area for crab farming is 2 to 20 mu. Fields should be chosen with fresh water quality, water sources and bottom soil free of industrial pollution, convenient irrigation and drainage, and ample sunlight. The bottom soil should preferably be clay loam, impermeable and non-leaking, with field ridges 0.8 to 1 m high and a slope of 1:2 or 1:2.5, and they must be tamped firmly to strictly prevent gaps from being left in the ridges, which would cause water leakage or crab escape.

Dig a ring ditch around the inner side of the field ridges, 2 to 3 m wide and 0.6 to 0.8 m deep, as the main site for crab farming. Field ditches must be dug well, in the form of a “cross” ditch or a “well” ditch, for crabs to crawl into the rice paddy to feed and hide. The dug ditches should each 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 megalopae or temporarily hold crab seed stock, and 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% to 15% of the total rice paddy area.

Escape-prevention facilities can be set up around the rice paddy used for crab farming as escape walls made of plastic boards or double-layer agricultural plastic film, usually 50 to 60 cm high, buried 10 to 15 cm into the soil, and supported and fixed with wooden stakes. The escape wall should tilt inward at an angle of 20 to 30 degrees.

The inlet and drainage gates must allow free irrigation and drainage, with water level easy to control and safe and reliable. The gates must be sealed with silk cloth to prevent crabs from escaping or harmful organisms from entering.

For the selection of rice varieties, choose varieties with strong fertilizer tolerance, hard stems, lodging resistance, a long growth period, and high yield. Varieties that do not require field drying should be given priority when selecting rice. If field drying is needed during river crab farming, it should be based on the principle of multiple short drying periods, and during field drying the water level should be lowered until the rice paddy surface is exposed above the water.