Polyculture Techniques for Silver Carp in Crayfish Ponds
AbstractPolyculture of crayfish and silver carp maximizes the use of water space. Crayfish are benthic animals that mainly move about on the bottom, while silver carp and bighead carp mainly inhabit the middle and upper layers of the water body. Silver carp do not need to be fed compound feed; they mainly feed on plankton in the pond, so this purifies the water quality of the shrimp pond while also reducing the harm plankton cause to crayfish, favoring crayfish growth and at the same time increasing extra income.
Polyculture of crayfish and silver carp is a measure that achieves multiple benefits at once: it purifies water quality, helps crayfish grow healthily, saves feed and increases income, and makes full use of the water space. However, polyculture of the two requires good pond construction work, selecting high-quality crayfish fry and silver carp fry for timely stocking, feeding according to the feeding habits of crayfish, and regulating water quality in a timely manner to keep the water quality fertile, lively, tender and refreshing. Do a good job of rotational harvesting and restocking of crayfish.
1. Pond construction. The pond area is 20 mu, with a water depth of about 1.5 m. The pond embankments must be compacted and have a certain slope. Use asbestos tiles or plastic sheets around the pond ridges to form a 0.5 m high anti-escape wall. Choose a pond with no pollution nearby, close to a water source, convenient for filling and draining, and with relatively little silt.
2. Pond preparation. In early March, apply 150-200 kg of quicklime per mu to splash and disinfect the whole pond. Ten days after disinfection, plant eelgrass and hydrilla in the pond. The planting method for eelgrass is to sow 0.1 kg of eelgrass seeds per mu; hydrilla is an asexually reproducing plant, so use the method of cutting stems into sections and inserting cuttings, planting 25-30 kg per mu. Moreover, the area of aquatic plants must not be too large; it should be controlled within 20-30% of the farming area. In this way, while providing concealed places for crayfish to rest and molt, it also purifies water quality, increases the dissolved oxygen content in the water, reduces fighting among crayfish, and provides crayfish with very fresh natural plant-based feed.
3. Shrimp fry stocking. The main source of crayfish seed stock is caught from natural waters at the end of September of the previous year. It is mainly small shrimp that did not reach market size that year or small shrimp that overwintered in ponds the previous year. Generally, the stocking time is from the end of March to early April, with a stocking density of about 7,000 per mu and a size of 200-250 per kg. Choose shrimp seed stock with a robust physique, agile movement, uniform size, complete appendages, and no disease.
4. Fish fry stocking. Generally, to control water quality and make full use of the plankton in the water, silver carp fry can be stocked in March, with 25 silver carp per mu and 5 bighead carp per mu, and the fry size is 150 g per fish.
5. Introduction of snails. In order to provide fresh, high-quality protein feed for crayfish, live snails need to be stocked in early April at a density of about 300 kg per mu. Additional stocking can also be done from the end of July to early August according to actual needs, at about 150 kg per mu.
6. Feeding and fertilization. Crayfish are omnivorous animals with a relatively large appetite and like animal-based feed, but they can also eat plant-based feed. They can be fed trash fish, the internal organs of livestock and poultry such as chickens, ducks and pigs, and wheat, corn and soybean meal, and can also be fed high-quality complete compound feed.
The amount of feed to be fed should be determined based on the weight and number of shrimp seed stock and the type of feed to determine the total annual demand. Crayfish grow relatively quickly from March to July, and during this period they need a relatively large amount of feed, accounting for 40% of the annual feeding amount. During high temperatures, crayfish grow very slowly, and the feed amount accounts for only 6-8%. From mid-to-late August to the end of October, the required feed amount accounts for about 50% of the whole year. Adopt the “four fixed and four observe” method for feeding. Starting from June, feed twice a day, once in the morning and once in the evening, mainly feeding in the evening, which can account for 60% of the daily feeding amount. The daily feed amount is 5% of the shrimp body weight.
The snails and aquatic plants in the pond will absorb the fertilizer in the water as they grow, making the water quality relatively lean. In order to allow organisms in the water to grow and reproduce normally, fermented fertilizer needs to be piled in the four corners of the pond in June-July, and stirred once every 1 week with a rake, so that the water quality has the characteristics of “fertile, lively, tender and refreshing.”
7. Regulating water quality. From April to June, each water fill should be controlled at about 20-30 cm, and the water should be changed once every 10-15 days, each time changing 1/3. Generally, the water change time is around 11 a.m. If the water is changed at this time, the water temperature difference between the river water and the pond water is not great, and the dissolved oxygen content can also be increased. During the peak growth period of crayfish, fertilizer can be applied once every 15 days, applying 10 kg of quicklime per mu per meter of water depth to increase the calcium content in the water. Use photosynthetic bacteria liquid once every 1 month to regulate water quality balance.
8. Timely harvesting. Strengthen pond management. In addition to normal pond inspections and prevention of disease and floating head, also do a good job of rotational harvesting and restocking of crayfish. Under normal circumstances, crayfish can be sold on the market 1 month after stocking, and catching tools such as shrimp cages and ground cages can be used. Starting from the end of May and early June, promptly catch adult shrimp that have reached market size for sale. Usually catch the large ones and leave the small ones, and additional juvenile shrimp of 4-5 cm can also be restocked, so that the water body is fully utilized and crayfish yield is increased.
Summary and Analysis of Experience
Polyculture of crayfish and silver carp makes full use of the water space. Polyculturing filter-feeding fish in shrimp ponds increases income while also maintaining ecological balance, preserving a good living environment, and reducing costs, and can increase returns by about 267.5 yuan per mu.
When feeding, it must be even to avoid crayfish fighting and killing each other while feeding. Livestock and poultry internal organs should be chopped up before feeding. Also insist on combining fine feed and green feed. If large numbers of crayfish climb onto the shore or aquatic plants, it means the water needs to be changed, especially in the middle and late stages of farming. Change the water 1-2 times a week so that the water contains sufficient dissolved oxygen. High-density farming requires attention to disease prevention, mainly giving priority to prevention and treatment, and strictly prohibiting the use of pesticides such as decis and trichlorfon.