Key Technical Points and Experience Sharing on Rotational Culture of Mandarin Fish and Freshwater Shrimp

Mandarin fish and freshwater shrimp are both currently popular species on the market, with large demand, high prices and high farming returns. Implementing rotational culture of mandarin fish and freshwater shrimp in ponds can maximize the use of the pond's idle period, fully utilize the water body and feed resources, increase output, and substantially raise pond production efficiency.

I. Pond Conditions and Preparation

1. Area The pond area should be 3-5 mu, rectangular, with a length-to-width ratio of 2.5:1, ideally oriented east-west, with a pond embankment width of 3-5 m, a pond slope ratio of 1:3 or more, and a flat pond bottom sloping slightly toward the drainage side to facilitate seine netting and pond drying for harvesting.

2. Water depth Water depth of 1.2-1.5 m is favorable for the growth of aquatic plants, photosynthesis, dissolved oxygen replenishment, and the habitat, feeding and growth of shrimp and fish; too deep is not suitable.

3. Water quality The water should be fresh and pollution-free, with a dissolved oxygen content of 4 mg/L or more and a pH of 7.5-9.

4. Drainage and irrigation system Drainage and irrigation should be separate, which is favorable for water quality regulation and disease prevention and control; the water source should be fresh and pollution-free.

5. Pond modification After the mandarin fish are harvested by drying the pond, dig a ditch 2 m wide and 0.5 m deep in the pond that connects with the drainage ditch as a shrimp collection trough, to facilitate harvesting by drying the pond.

II. Mandarin Fish Fingerling Rearing

1. Configuration of forage fish for mandarin fish fingerlings Allogynogenetic silver crucian carp fry are selected as forage fish. Around April 10, the crucian carp are ponded by conventional methods, and by early May they reach a size of about 20,000 fry per kg, which is suitable forage for mandarin fish.

2. Stocking of mandarin fish summer fry In May, mandarin fish summer fry are stocked at a density of 2,000 per mu; the forage fish are co-cultured in the same pond as the mandarin fish, that is, mandarin fish and forage fish are co-cultured at a ratio of 1:200-300. This density can provide the mandarin fish with sufficient forage, meet their feeding needs and promote growth. To meet the growth needs of the forage fish, 1 kg of soybean or soybean cake plus 10 g of water-ground soybean milk or soybean cake slurry is fed once a day. In this way, after about 1 month of intensive rearing, the survival rate of mandarin fish reaches over 70%, and about 1,500 large-size mandarin fish fingerlings of over 5 cm can be produced per mu.

III. Commercial Mandarin Fish Culture

1. Stocking of large-size mandarin fish fingerlings and forage fish After about 1 month of intensive rearing of the mandarin fish fingerlings, drain 70% of the pond water, use a seine net, catch and count them, and retain them at a density of 500-800 per mu to switch to commercial mandarin fish culture; surplus mandarin fish fingerlings are sold. When stocking mandarin fish fingerlings, silver crucian carp summer fry are stocked at a density of 5,000 per mu, and some wild miscellaneous fish with strong reproductive capacity are appropriately stocked to reproduce multiple times to supplement the shortage of forage fish and enhance the self-supply capacity of forage fish in the mandarin fish culture pond.

2. Feeding management During the mandarin fish grow-out stage, an intermittent forage fish feeding method is adopted: once every 10-15 days in the early and late stages, and once every 7-10 days in the middle stage, feeding about 50 kg per mu of water surface each time, ensuring the ratio of mandarin fish to forage fish is 1:8. If forage fish are too sparse, mandarin fish will consume excessive energy chasing forage fish, which is not conducive to fattening; if forage fish density is too high, the total oxygen consumption will increase, easily causing mandarin fish to gasp for air due to hypoxia, which is likewise not conducive to mandarin fish growth. During the culture process, a total of 1,200 kg of forage fish are fed per mu, producing 280 kg of mandarin fish, with a feed coefficient of about 4. After more than 4 months of rearing and management, by mid-October most have reached 0.4-0.45 kg, at which point they can be harvested in batches for market; by mid-October the pond can be dried for harvesting, with a commercial rate of over 85% and a survival rate of over 95%.

IV. Autumn Adult Shrimp Culture

1. Stocking of freshwater shrimp fry After the mandarin fish pond is dried, 5-7 days before stocking shrimp fry, fill the pond with 0.5-0.6 m of water, then apply base fertilizer. The fertilizer can be fermented poultry and livestock manure, at 150-200 kg per mu, to cultivate natural food organisms as suitable feed for shrimp fry. Generally, 8-10 kg per mu of freshwater shrimp fry at a size of 2,000-4,000 per kg are stocked. Freshwater shrimp have by this time passed their peak breeding period, so their numbers can be controlled.

2. Setting up netting Freshwater shrimp like to inhabit shallow water areas and cluster and crawl along the pond edge and beach foot. In the process of pond culture of freshwater shrimp, only the shallow water areas of the pond slope and beach foot are utilized, and the water space in the middle of the pond cannot be fully used. To overcome this shortcoming, netting is set up in the pond to fully utilize the pond space and water body, thereby improving the size and culture yield of freshwater shrimp. The area of netting set up is about 20% of the total pond area. The netting uses 1-2 m wide wide-mesh netting, set 0.4-0.5 m below the water surface, sloping slightly toward the pond bank foot, with even spacing. The netting should be set up 3 days before stocking the shrimp fry.

3. Reasonable feeding The main feed variety is high-quality special pelleted feed for freshwater shrimp, with particle size fine at first and coarse later, and quality fine at first and superior later. Within one month after the shrimp fry are put into the pond, for the first half month use full-price crushed No. 1 feed at 0.5-1 kg per mu per day, and for the latter half month use No. 2 feed at 1.5-2 kg per mu per day, then switch to No. 3 feed, while supplementing with green bran, wheat bran, soybean cake, minced fish, silkworm pupae, crushed snails, etc. The daily feeding amount is calculated according to the shrimp body weight in the pond, generally 15%-20% in the early stage, 8%-10% in the middle stage, and 5%-6% in the late stage; the actual amount should be controlled so that the shrimp finish eating within 2-4 hours. The feeding method is generally twice a day: at 8-9 a.m., accounting for 30% of the whole day's feeding amount, fed in the middle of the pond; and at about 5 p.m., accounting for 70% of the whole day's feeding amount, fed around the pond and on the netting. Feeding should achieve "four looks" - look at the season, look at the weather, look at the water quality, look at shrimp activity and growth; and "four fixes" - fixed time, fixed location, fixed quality, fixed quantity.

V. Water Quality Management Whether culturing mandarin fish or shrimp, the dissolved oxygen requirement in the water is relatively high, so water quality regulation must be emphasized during the culture process, with the core being to always maintain a high dissolved oxygen level.

1. Mandarin fish culture The oxygen consumption rate of mandarin fish is almost twice that of domestic fish, and when the dissolved oxygen content is below 5 mg/L, they will gasp for air at the surface. Therefore, during the culture period, replace part of the pond water once every 3-5 days to keep the water depth at about 1.5 m and the transparency at 35-45 cm, which is favorable for mandarin fish feeding. In stuffy and thunderstorm weather, appropriately increase aeration to ensure sufficient oxygen in the pond and avoid mandarin fish gasping for air due to hypoxia.

2. Freshwater shrimp culture The shrimp pond water quality should be fresh, with high oxygen content and free from pollution. In the early stage, focus on fertilizing the water, with transparency of about 25 cm; in the middle and late stages, frequently add or change water, with transparency of about 35 cm; water changes are generally carried out on sunny afternoons. During the growth period, alternately use calcium superphosphate and quicklime once every 20 days, with per-mu amounts of: calcium superphosphate 3-5 kg, quicklime 10-15 kg. Never mix the two or use them at the same time.

VI. Prevention and Control of Diseases and Enemies

1. Mandarin fish culture

(1) Trichodiniasis Within two months after stocking mandarin fish summer fry, apply a mixture of copper sulfate and ferrous sulfate (5:2) once every half month, at a concentration of 0.7×10-6.

(2) Dactylogyriasis Around mid-June, when mandarin fish have grown, large numbers of Dactylogyrus parasitize them, causing the mandarin fish body color to turn black, gills to swell, and the body to become thin and stop feeding. A concentration of 0.1×10-6 of crystalline trichlorfon can be splashed to prevent it; pay attention to temperature and weather conditions when splashing.

(3) Sinergasiliasis When mandarin fish are cultured to mid-September, a concentration of 0.25 mg/L of Qiangli Miechongjing Type I can be splashed to prevent it.

2. Freshwater shrimp culture In freshwater shrimp culture, if black gill disease and incomplete molting disease occur, 15 kg of quicklime per mu can be splashed over the whole pond. If wild miscellaneous fish such as carp, crucian carp and loach appear, they must be removed in time; generally, 0.5 kg per mu of "Qingtangjing" per meter of water depth can kill all wild miscellaneous fish without affecting the survival of freshwater shrimp. If green algae appear in the pond, they endanger the survival of freshwater shrimp and affect their quality; at present, the effective method is to use "high-efficiency green algae remover", 45 g per mu per meter of water depth, splashed where the green algae grow; after three days the green algae all disappear, which is favorable for freshwater shrimp growth.

VII. Harvest Following this model for rotational culture of mandarin fish and freshwater shrimp, 1,500 large-size mandarin fish fingerlings of over 5 cm can be produced per mu, with a survival rate of over 70%; half are retained and raised to mid-October, producing 285 kg of commercial mandarin fish per mu, with a survival rate of 95% and a commercial rate of over 85%. Freshwater shrimp are cultured until early April of the following year, producing 75 kg of commercial shrimp of about 200-250 per kg per mu.