Detailed Explanation of the Key Technical Points for Polyculture of Crayfish in Wild Rice Stem Fields

As people's aquaculture levels continue to improve and aquaculture techniques continue to innovate, many new farming models have emerged. Polyculture is currently quite popular and is also a relatively new type of farming model. Polyculture can not only improve farming efficiency, but also allow one pond to serve multiple uses, effectively reducing farming costs.

Key Technical Points for Polyculture of Wild Rice Stem and Crayfish

1. Pond selection: Ponds with sufficient water sources, no pollution, convenient drainage, strong water retention, deep plough layers, medium to above-average fertility, and an area of more than 1 mu can all be used for planting wild rice stem and raising shrimp.

2. Shrimp pit construction: Along the inner side of the ridge, dig a ring-shaped shrimp pit 1.5 m-2.0 m wide and 0.5 m-0.8 m deep. For larger ponds, a middle ditch should also be appropriately dug in the middle, with the middle ditch 0.5 m-1 m wide and 0.5 m deep. The total area accounts for 8% of the pond area, and the maximum area of each shrimp pit shall not exceed 200 sq m. Before stocking red swamp crayfish, mesh barrier facilities must be installed at the pond's inlet and outlet. 3. Anti-escape facilities: The anti-escape facilities are simple. Bury hard plastic film 20 cm into the soil, leaving 50 cm exposed above the soil. On the outer side of the plastic film, fix it with bamboo strips or wooden stakes about every 1 m. 4. Fertilization: Apply base fertilizer before planting wild rice stem from February to March each year. Well-rotted pig and cattle manure and green manure at 1500 kg/mu, calcium magnesium phosphate fertilizer at 20 kg/mu, and compound fertilizer at 30 kg/mu can be used. Turn them into the soil layer, rake level and fine, integrate fertilizer and mud, and then transplant wild rice stem seedlings.

5. Select good wild rice stem seedlings: From mid-September to early October, during the autumn wild rice stem harvest, carry out seed selection, choosing robust plants with medium height, flat stems, and high purity as seed retention plants. 6. Timely transplanting: From late March to mid-April, dig up the wild rice stem clumps and split them along the tillering points with a sharp blade into several small clumps. Each clump should carry stolons and 4-6 robust tiller buds, cut off the leaves, and retain leaf sheaths 16 cm-26 cm long to reduce evaporation and help early survival. Dig, divide, and plant as you go. The plant and row spacing depends on the planting period, the number of divided seedlings, and the number of harvests. Double-season wild rice stem adopts wide and narrow row planting, with a wide row spacing of 1 m, a narrow row spacing of 80 cm, and a hill spacing of 50 cm-65 cm, 1000-1200 hills per mu, with 6-7 seedlings planted per hill. The planting method is preferably oblique insertion at 45 degrees, with the depth such that the rhizome and tiller base enter the soil while the tiller shoot buds are just slightly exposed above the water surface. 7. Stocking red swamp crayfish: Disinfect the shrimp pits 10 days before transplanting the wild rice stem seedlings. For newly built shrimp pits, they must first be soaked in clean water for 7-10 days, then replaced with fresh water and soaked for another 7 days before shrimp can be stocked. Each mu can stock 0.5-1 ten-thousand juvenile crayfish 2 cm-3 cm long. The juvenile shrimp should be placed in shallow water and water hyacinth floating planting areas. When stocking shrimp seed, soak the shrimp seed in 3%-5% salt water for 5 minutes to prevent shrimp diseases. At the same time, stock 20 kg-30 kg of snails per mu and feed 1.0 kg-2.5 kg per mu.

8. Scientific management: 1. Water quality management: Follow the principle of “shallow-deep-shallow” (shallow water for planting, deep water for survival after planting, shallow water for tillering). Before sprouting, irrigate 30 cm; after planting, maintain a water depth of 50 cm-80 cm; before tillering, shallow water of 80 cm is still suitable to promote tillering and root development; by the late tillering stage, deepen the water to 100 cm-120 cm to control ineffective tillering. During the high-temperature period from July to August, maintain a water depth of 130 cm-150 cm. 2. Scientific feeding: Supplement with concentrated feed according to the season, such as rapeseed cake, bean dregs, wheat bran, rice bran, earthworms, fly maggots, fish pellet feed, and other aquatic animals. You can feed self-made mixed feed or purchase special fish feed, and you can also feed some animal-based feed, such as snail and mussel meat, fish meat, earthworms, or collected cladocerans, copepods, and slaughterhouse offal, feeding at fixed points and multiple points along the shallow water areas around the pond edge. The feeding amount is generally 5%-10% of the fish and shrimp body weight, adopting the “four fixed” feeding method, with evening feeding accounting for 70% of the total daily amount. Feed twice a day, once at 8-9 in the morning and once at 18-19 in the evening. 3. Scientific fertilization: Base fertilizer commonly uses human and livestock manure and green manure. Topdressing mostly uses chemical fertilizers, preferably in small amounts many times. Urea, compound fertilizer, potassium fertilizer, etc. can be selected, and ammonium bicarbonate is prohibited. Organic fertilizer should account for 70% of the total fertilizer amount. 4. Wild rice stem medication: Select pesticides according to the symptoms that are highly effective, low in toxicity, low in residue, and have no effect on the co-cultured crayfish. After application, replace and add fresh water in time. It is strictly prohibited to spray pesticides at noon during high temperatures. 9. Harvesting: Wild rice stem can be divided by harvest season into single-crop wild rice stem and double-crop wild rice stem. After harvesting the wild rice stem, use your hands to bank the rotten mud in the clump onto the plant stems. Generally, the yield of wild rice stem is 750 kg-1000 kg per mu. Crayfish can be harvested with ground cages and shrimp cages. Generally, the yield of crayfish is 200 kg per mu.

Living Habits of Crayfish  

Crayfish are nocturnal animals that live by crawling along the bottom. They inhabit lakes, rivers, reservoirs, swamps, ponds, and ditches, and are sometimes also found in rice fields. However, they are more common in still-water ditches, ponds, and shallow lakes with relatively abundant food. Their habitats are mostly soil-based, with more hidden objects such as aquatic plants, tree roots, or stones. During the day, they often hide in darker corners at the bottom of the water, beside stones, in grass clumps, or in caves, and come out at night to feed.  

Under natural conditions, due to lack of bait and low water transparency, they can also be seen foraging during the day. This shrimp has strong climbing ability and burrowing ability. When the water body is short of oxygen, lacks food, is polluted, or when other biological, physical, and chemical factors change sharply and become unsuitable, it often climbs out of the water and enters another water body. For example, when it rains, especially during heavy rain, this shrimp often climbs out of the water to move around. During the growth period, crayfish basically do not dig burrows. The longest crayfish burrow can reach 100 cm, and the diameter can reach 9.2 cm. Crayfish can use artificial caves, original caves in the water body, and other hidden objects. Their burrowing behavior mostly appears during the breeding period. Therefore, appropriately adding artificial nests in the culture pond and applying technical measures can greatly reduce the destructive effect of this shrimp on pond ridges and embankments.  

Crayfish are widely distributed in various water bodies, especially in still-water ditches, shallow lakes, and ponds. This shows that this shrimp has strong adaptability to eutrophication and low oxygen in water bodies. Generally, maintaining dissolved oxygen in the water body above 3 mg/L can meet its growth needs. This shrimp can survive for more than a week after leaving the water body.  

Crayfish have strong adaptability to both high and low water temperatures. This is consistent with its distribution across tropical, subtropical, and temperate regions. Its temperature adaptation range is 0°C-37°C. In the Yangtze River basin, if it is placed outdoors with water on winter nights and frozen, it can still survive, but the optimum temperature range for crayfish is 18°C-31°C.   

What Issues Should Be Noted When Raising Crayfish  

1. Seed stock: There is no “hybrid variety” of crayfish. At present, natural seedlings are abundant and cheap, while artificial seedlings are still at the laboratory stage. In addition, do not mistakenly believe that they are a new variety that has been domesticated and shows less mutual killing, and therefore buy crayfish seed from other places at high prices. Many people also think that as long as seed crayfish are stocked in the first year, they will continue to reproduce on their own and obtain good returns year after year. In fact, crayfish farming has the highest yield in the first year after stocking, and then declines year by year. Because the crayfish life cycle is 16-18 months, combined with inbreeding, functional degeneration, and decreased disease resistance, after 3 years the yield will drop sharply or even result in total loss.  

2. Water quality: Some people think that crayfish can grow very well even in smelly ditches. In fact, it is not that both good and bad water can be used for farming. Fresh water quality is the key to high-yield crayfish farming. It is required that the coverage of aquatic plants in the pond be 30-60%, the water transparency be about 30 cm, and the dissolved oxygen be >5 mg/L. Water should be changed regularly, with 1/3 changed each time, and the water level should be kept above 80 cm in high-temperature seasons.  

3. Feed: Crayfish are omnivorous organisms that favour animal-based bait. Whether they grow well depends on protein intake. Fresh small trash fish and field snails can be used as the main feed, supplemented by plant-based bait. Compound feed with a protein content of no less than 32% can also be fed. Rotten and spoiled animal and plant feed should not be fed, because its utilization rate is low and it easily deteriorates water quality.  

4. Diseases: Some people think that “crayfish do not get sick.” In fact, this is not true. After high-density farming, various environmental factors can easily cause crayfish to become diseased. The solution is mainly prevention, with regular use of drugs. During the farming process, the water body should be disinfected regularly. If the water body pH is <7, every 15-20 days, slake quicklime into slurry at a concentration of 20 g/cubic meter and splash it evenly. Generally, ponds should be disinfected once every 15-20 days with chloride substances, etc., and about every half month add molting growth promoter to the feed and feed continuously for 3 days.  

5. Polyculture: Many people, in order to reasonably use space and improve farming efficiency, think that crayfish can be polycultured with fish. In fact, crayfish must never be polycultured with carnivorous or omnivorous aquatic products. This is because crayfish are most easily eaten by others when molting, and when crayfish give birth, silver carp and bighead carp are both their natural enemies, so polyculture is not advocated. 

Construction of Crayfish Farming Sites  

1. Farming environment  

Crayfish farming sites should be selected in places with ventilation and sunshine, a quiet environment, sufficient and pollution-free water sources, abundant bait sources, convenient drainage and irrigation, and convenient transportation and power supply. Water from rivers, lakes, reservoirs, and ponds can be used as the water source, and well water and spring water can also be used. The pH value of the water quality should be about 6-8.  

2. Shrimp pond environment  

Crayfish farming ponds can be large or small, with a water depth of 0.6-1.5 m, preferably oriented east-west and facing the sun. The surroundings inside the pond should have a slight slope, and the pond bottom should be flat, with a slight incline toward the drainage outlet side to facilitate draining the pond water. The surroundings of the pond must be soil-sloped, mainly for crayfish to dig holes and inhabit so they can safely overwinter. The pond ridge should be 40-50 cm above the water surface, and the width of the pond ridge should reach 1 m, mainly to prevent crayfish from digging holes and causing water leakage. If the pond area exceeds 10 mu, 1-2 additional field ridges can be built in the pond, distributed evenly in field, well, or cross shapes, mainly to let crayfish dig holes, inhabit, and spawn. Crayfish like nighttime activity and crawling along the ground, so on the outer periphery of the pond ridge, use asbestos tiles, plastic film, etc., with wooden stakes as supports, to build a 50 cm high anti-escape wall, with the bottom buried about 30 cm into the soil and sealed tightly, ensuring that no crayfish can escape.  

3. Pond disinfection  

The commonly used disinfection method for crayfish farming ponds is quicklime disinfection. During disinfection, leave only 5-10 cm of water in the pond, mix quicklime into slurry and evenly sprinkle it into the pond water to dissolve. The usual amount of quicklime is 25-40 kg per mu. On the second day after using quicklime, use an iron rake to stir the pond bottom so that the lime slurry and silt are fully mixed. Do not drain the disinfected water; keep it in the pond, start adding water the next day, and stop when the water level meets the rearing requirements. At the same time, crayfish molt during growth and must intake sufficient calcium. Quicklime has a calcium content of more than 50% (theoretical value 71.4%), and it is cheap and has good application results.

Although polyculture is currently a relatively good farming model, there are still many points that need attention. After all, when two different things are farmed together, they each have their own needs and growing environments. Only by achieving both independent growth and peaceful coexistence can greater profits be created.