A Detailed Guide to Crayfish Stocking Methods and Precautions

There is a lot of preparatory work to do before stocking crayfish. Crayfish cannot simply be stocked and then raised; their farming requires certain techniques and skills, and only by mastering these techniques and skills can their benefits be maximized.

Preparatory work before stocking crayfish

1. Conditions and preparation of the paddy field. The paddy field should be large, generally from several dozen mu to over a hundred mu. The field ridges should be relatively high, able to hold a water depth of 50-80 cm. Along the inner edge of the field ridges, dig a ditch 1-1.5 m wide and 0.8 m deep around the perimeter. For larger fields, a "cross"-shaped or "well"-shaped ditch should also be dug in the middle, with a ditch width of 0.5-1 m and a depth of 0.5 m. 10-15 days before stocking the crayfish, apply 50 kg of quicklime per mu to the crayfish-raising ditch in the paddy field, or choose other chemicals, to thoroughly clear and disinfect the rearing ditch, killing wild trash fish, harmful organisms, and pathogenic bacteria.

2. Apply sufficient base fertilizer. 7-10 days before stocking the crayfish, fill the field ditch with 50-80 cm of water, then apply fertilizer to cultivate food organisms. Generally, apply 50 kg of compound fertilizer and 50 kg of ammonium bicarbonate per mu; farmyard manure has a slow and long-lasting effect, has no impact on the growth of crayfish after application, and can also reduce the frequency and amount of chemical fertilizer applied later. Therefore, if farmyard manure is available, it is best to apply it, at 1000 kg per mu, applied all at once in sufficient quantity.

3. Transplant aquatic plants. Plant submerged aquatic plants such as hornwort and coontail in the crayfish ditch, or plant water spinach, water hyacinth, etc. along the ditch edges. However, the area of aquatic plants must be controlled. Generally, aquatic plants should account for 10%-20% of the crayfish ditch area, and it is best for them to be scattered rather than clustered together, which helps keep the water flow in the crayfish ditch unobstructed.

4. Filtration and escape prevention. Bamboo screens, wire mesh, and netting should be installed at the water inlet and outlet as escape-prevention and filtration facilities, strictly preventing harmful organisms from entering.

Crayfish stocking methods

When stocking crayfish fry or crayfish seed stock, test the water first, and only after the water is safe can the crayfish be released. There are several crayfish stocking methods:

First, immediately after the rice harvest in early September, directly stock brood crayfish into the paddy field to let them reproduce on their own. According to the actual conditions of paddy field farming, generally stock 20 kg of crayfish per mu with individuals above 40 g each, at a female-to-male ratio of 3:1 or 7:2. When transplanting rice seedlings the following season, use no-till rice cultivation.

Second, after rice transplanting in May, release juvenile crayfish with a size of 2-4 cm, at 5000-10000 individuals per mu. When stocking crayfish, pay attention to the quality of the young shrimp; the stocking size within the same field plot should be as uniform as possible, and the full amount should be released at one time.

Crayfish stocking methods and precautions

1. Field management. When raising crayfish in paddy fields, besides applying sufficient base fertilizer, feeding is not required. However, during the peak growth season of crayfish, some animal-based feed may be appropriately provided, such as crushed snails, mussels, and slaughterhouse scraps. Insist on patrolling the field every morning and evening to observe changes in water color in the ditch and the shrimp's activity, feeding, and growth conditions.

2. Drying the field. When drying the paddy field for rice, it should be lightly baked, and the field water must not be completely drained. Lower the water level until the field surface is exposed, and keep the duration short. If abnormalities are found in the crayfish, immediately add water.

3. Fertilizing the paddy field. The base fertilizer for the paddy field should be sufficient, mainly applying decomposed organic fertilizer, applied all at once into the plow layer before transplanting rice seedlings, to achieve the goal of lasting and long-term fertility. Topdressing is generally done once a month, with 5 kg of urea per mu, 10 kg of compound fertilizer per mu, or organic fertilizer composted from human and livestock manure, which has no adverse effect on crayfish. Do not use fertilizers harmful to crayfish, such as ammonia water and ammonium bicarbonate.

4. Applying pesticides to rice. Crayfish are very sensitive to many pesticides. The principle of raising shrimp in paddy fields is to resolutely avoid pesticides when possible, and when pesticides are needed, choose highly effective and low-toxicity pesticides and biological agents. When applying pesticides, strictly control the safe use concentration of the pesticide to ensure the safety of the shrimp, and require spraying onto the rice leaf surface, trying not to spray into the water, and it is best to apply pesticides by zones.

5. Planting grass. Transplant aquatic plants into the ring ditch and field ditch, such as tape grass, hornwort, coontail, and other submerged plants. For crayfish rearing ditches in paddy fields, the aquatic plant coverage should preferably be 10%-20%, and it is best to be scattered and dispersed.

6. Preventing escape and disease. When 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. During the flood season, prevent the field from being flooded over, which could cause shrimp escapes.

7. Harvesting. When raising crayfish in paddy fields, as long as the crayfish seed stock is released in sufficient quantity at one time, after 2 months of rearing, some crayfish will reach marketable size. Long-term harvesting and harvesting the large while leaving the small is an important measure to reduce costs and increase output. Harvest crayfish that have reached marketable size for sale on the market, and keep those that have not reached size in the paddy field for continued rearing, reducing the density of crayfish in the paddy field and promoting the rapid growth of small-sized crayfish.

Misconceptions to avoid in crayfish farming  

1. Regarding seedlings and seed stock: what is currently called crayfish can also be called red swamp crayfish or Japanese red swamp crayfish; they are all one species, and there is no such thing as a "hybrid variety." Because the cost is too high and natural seedlings are currently abundant and cheap, while artificial seedlings are still at the laboratory stage; in addition, do not mistakenly believe that it is a new variety that has been domesticated and shows less cannibalism, and therefore buy crayfish seed stock from other places at high prices.  

Many people believe that after investing in brood crayfish in the first year, they will obtain good returns year after year through continuous self-reproduction. In fact, crayfish farming has the highest output in the first year after stocking, and then declines year by year. Since the crayfish life cycle is 16-18 months, combined with inbreeding, functional degeneration, and reduced disease resistance, after 3 years the output will drop sharply or even result in total loss.  

2. Regarding water quality: some people think that crayfish can grow very well even in stinking ditches. In fact, it is not that they can be raised in either good or bad water; 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%. Water transparency should be around 30 cm, dissolved oxygen >5 mg/L, and water should be changed regularly, with 1/3 changed each time. In high-temperature seasons, the water level should be kept above 80 cm.  

3. Regarding feed: crayfish are omnivorous organisms that favor 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, and 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. Regarding disease prevention and control: some people believe that "crayfish do not get sick," but this is not true. After high-density farming, various environmental factors can easily cause crayfish disease. The solution is mainly prevention, with regular use of medication. During the farming process, the water body should be disinfected regularly. If the water pH is <7, every 15-20 days, slake quicklime into a slurry at a concentration of 20 g per cubic meter and sprinkle it evenly. Generally, ponds should be disinfected once every 15-20 days with chloride, etc., and about every half month add molting-promoting hormone to the feed and feed continuously for 3 days.  

5. Regarding mixed culture: many people, in order to make reasonable use of space and improve farming efficiency, believe 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 preyed upon when molting, and when crayfish are spawning, silver carp and bighead carp are both their natural enemies, so polyculture is not advocated.  

6. Regarding management: some farmers believe that because crayfish are omnivorous, they can simply be fed casually. Therefore, some people do not even feed bait in intensive crayfish ponds, causing crayfish to prey on each other; or they feed excessive animal offal, causing organic matter to ferment, the water body to stink, and toxic gases and oxygen deficiency to occur, leading to farming failure.  

7. Regarding yield per mu: "Crayfish yield per mu is closely related to stocking density, farming environment, feeding amount, disease prevention and control, and so on. Crayfish grow quickly, and generally can be sold after 50-70 days of farming. May-June is the peak sales season. After the end of June, they begin mating, spawning, and burrowing, and the catch drops sharply. Therefore, rumors such as crayfish farming yields exceeding a thousand jin and profits of tens of thousands, similar to the 'Dragon King 811' claim, are really not credible. Generally speaking, crayfish farming yield is about 250-450 jin per mu, with an output value of 1500-2500 yuan.    

Although crayfish farming is a project with a very low threshold and relatively low risk, as long as certain techniques and methods are mastered in the crayfish farming process, it can produce twice the result with half the effort, and only then can the farming be done better and on a larger scale.