Detailed Explanation of Key Technical Points for Crayfish Farming in Rice Paddies

Crayfish prices soared this summer, with night snack stalls across the market unable to meet demand, and many crayfish farmers made substantial profits. Below, we introduce the techniques for farming crayfish in rice paddies.

I. Field Plot Selection

It is advisable to choose field plots with abundant water sources, convenient irrigation and drainage, good and pollution-free water quality, and strong water retention capacity for crayfish farming. The area can range from a few mu to dozens or even hundreds of mu; larger areas are better.

II. Field Engineering Construction

The field engineering construction for crayfish farming in rice paddies includes reinforcement of field ridges, escape-prevention facilities at water inlet and outlet, ring ditches, field ditches, shade sheds, and other works. Dig crayfish farming ditches along the inner side of the field ridges all around, with a ditch width of 1 m to 2 m, a depth of 0.8 m to 1 m, and a slope ratio of 1:2.5. For larger field plots, also dig “field”-shaped and “well”-shaped field ditches in the middle of the field and add several small ridges. The field ditches should be 0.5-1 m wide and 0.5 m to 0.6 m deep; the small ridges are used for managing rice. The area of crayfish farming ditches and field ditches accounts for about 5%-10% of the rice paddy area. Use the soil dug from the crayfish farming ditches to reinforce and raise the field ridges and level the field surface. When reinforcing the field ridges, each layer of soil added must be compacted to prevent the ridges from collapsing due to rain erosion.

The top of the field ridges should be more than 3 m wide and raised by 0.5-1 m. The water inlet and outlet should be enclosed with wire mesh or fences to prevent crayfish from escaping with the water flow. The water inlet channel is built on the field ridge, and the water outlet is built at the lowest point of the crayfish ditch, following the pattern of high irrigation and low drainage to ensure water can be let in and drained out. Additionally, at 1 m from the field ridge, drive a 1.5 m high stake every 3 m, set up with moso bamboo, and plant melons, beans, gourds, etc. along the edge of the field ridge. After the vines climb the trellis, they provide shade and heat relief in the hot summer.

III. Preparatory Work Before Stocking

1. Ditch clearing and disinfection. 10 to 15 days before stocking crayfish, use 50 kg of quicklime per mu of rice paddy crayfish farming ditch, or choose other drugs, to thoroughly clear and disinfect the rearing ditches and kill wild miscellaneous fish, harmful organisms, and pathogenic bacteria.

2. Apply sufficient base fertilizer. 7-10 days before stocking crayfish, fill the field ditches with water to a depth of 50 cm to 80 cm, and use 50 kg to 75 kg of quicklime per mu of rice paddy crayfish ditch for splashing disinfection. Then apply fertilizer to cultivate water; generally apply 50 kg of compound fertilizer, 59 kg of ammonium bicarbonate, or 200 kg to 500 kg of farmyard organic fertilizer per mu.

3. Transplant aquatic plants. Plant submerged aquatic plants such as Hydrilla verticillata and Potamogeton malaianus in the crayfish ditches, or plant water spinach, water hyacinth, etc. along the ditch edges. The aquatic plant area should account for 20%-25% of the crayfish ditch area, preferably distributed in scattered patches.

4. Filtration and escape prevention. Install bamboo screens, wire mesh, and netting at the water inlet and outlet as escape-prevention and filtration facilities to strictly prevent harmful organisms from entering.

IV. Stocking of Crayfish Fry and Breeders

Before stocking crayfish fry and breeders, test the water; only after the water test is safe can juvenile crayfish be released. There are several stocking methods:

First, in July of the previous year, directly stock parent crayfish in the rice paddy to let them reproduce on their own. According to the actual conditions of the rice paddy, generally stock 20 kg of parent crayfish of 40 g or more per mu, with a female-to-male ratio of 3:1. In the second year, adopt no-till rice planting so that the hatched juveniles can directly feed on plankton in the rice paddy water, improving the hatching rate of juveniles and the survival rate of young crayfish;

Second, after rice transplanting in May, release juvenile crayfish. Generally stock 5,000 to 8,000 juvenile crayfish of 2-4 cm per mu. When stocking, soak the crayfish in 3% salt water for about 3 minutes. While ensuring the quality of crayfish fry and breeders, the same field plot must be stocked with crayfish fry and breeders of the same size, and stocked sufficiently in one go.

V. Field Management

When raising crayfish in rice paddies, in addition to applying sufficient base fertilizer, artificial feed is not required. Some aquatic plants can be placed in the crayfish ditches, and during the peak growth season of crayfish, some animal feed can be appropriately fed, such as crushed snails, clams, and offal from slaughterhouses. Persist in patrolling the field every morning and evening to observe changes in water color in the ditches and the activity, feeding, and growth of crayfish. Field management work mainly focuses on rice water retention, field drying, fertilization, pesticide application, and crayfish escape prevention and harm prevention.

1. Field drying. Rice field drying should be lightly baked, with the water level lowered until the field surface is exposed, and the time should be short. If abnormal reactions of crayfish are found, water must be added immediately.

2. Fertilization of rice paddies. Rice paddy base fertilizer should be applied into the plow layer all at once before transplanting to achieve long-lasting fertility. Topdressing should be applied in small amounts multiple times, preferably applying to one half first and then the other half. Generally topdress once a month, applying 5 kg of urea, 10 kg of compound fertilizer, or 30 kg to 50 kg of fermented livestock and poultry manure per mu. Never apply ammonia water or ammonium bicarbonate as topdressing. When applying topdressing, it is best to first drain the field water shallow to concentrate the crayfish in the ring ditches and field ditches, then apply fertilizer, so that the chemical fertilizer quickly settles into the bottom field mud and is absorbed by the field mud and rice, then immediately deepen the field water to normal depth.

3. Pesticide application to rice. The principle of crayfish farming in rice paddies is to resolutely avoid pesticide use when possible, and when pesticide use is needed, choose high-efficiency and low-toxicity pesticides, avoiding insecticides containing pyrethroids. When applying pesticides, strictly control the safe use concentration, spray the pesticide on the rice stems and leaves, try not to spray it into the water, and it is best to apply pesticide by zones. To control rice stem borers, use 200 mL of 18% bisultap aqueous solution per mu plus 75 kg of water for spraying; to control rice planthoppers, use 50 g of 25% buprofezin wettable powder per mu plus 25 kg of water for spraying; to control rice bacterial leaf streak and rice blast, use 40 g of 50% Xiaojunling per mu plus water for spraying. At the same time, add water to the field to 20 cm before pesticide application, and replace the water promptly after spraying.

4. Escape prevention and disease prevention. Persist in patrolling the field every day, check whether the screen mesh at the water inlet and outlet is firm and whether the escape-prevention facilities are damaged, prevent field overflow during flood season, and prevent crayfish from escaping. When letting in and draining water, use 40-mesh to 80-mesh silk screen mesh for filtration to prevent harmful organisms from entering the field. Usually remove enemies such as frogs, water snakes, loaches, rice field eels, and water rats to prevent them from harming crayfish.

VI. Feeding Management

Generally from July to September, feed plant-based feed such as rapeseed meal, wheat bran, aquatic and terrestrial grasses, melon rinds, and vegetables; from October to December, feed more animal-based feed. The daily feeding amount is 6%-8% of the crayfish body weight, fed once each in the morning and evening, with 70% of the daily ration fed in the evening. In winter, feed once every 3 to 5 days, around sunset, with a feeding amount of 1%-2% of the crayfish body weight. Starting from April of the following year, gradually increase the feeding amount to ensure crayfish eat enough and eat well, so as to avoid pesticide harm to the crayfish body.

Water management: Apart from field drying, the rice paddy water depth should generally be maintained at about 20 cm, and new water should be frequently added and exchanged. Water should generally be added to the rice paddy from 10 a.m. to 11 a.m., keeping the temperature of the incoming water close to the rice paddy water temperature. When adding water, drain while irrigating so that the temperature difference is not large.

At the end of June, exchange 1/5 to 1/4 of the water weekly; from July to August, exchange water 3 to 4 times per week, with the exchange amount about 1/3 of the field water; after September, exchange water once every 5 to 10 days, exchanging 1/4 to 1/3 each time, maintaining the water transparency in the crayfish ditches at 25 cm to 30 cm. In the field ditches, splash quicklime water once every 15 to 20 days, with 5 kg to 10 kg per mu each time, to regulate water quality.

If conditions permit, regularly add appropriate amounts of Vc, Ve, and Ca to the feed to enhance the disease resistance and immunity of crayfish.

VII. Harvesting

For crayfish farming in rice paddies, generally after about 2 months of rearing, some crayfish can reach commercial specifications and can be harvested frequently, harvesting the large ones and leaving the small ones. Harvesting tools include ground cages, shrimp cages, maze traps, etc. The tools can be placed in the field ditches at night, and the crayfish collected the next morning.