Detailed Explanation of Mandarin Fish Contiguous Pond Aquaculture Technology
1. Living habits of mandarin fish: A bottom-dwelling fish, living in still water and rivers, lakes and reservoirs with a certain flow, especially in shallow lakes with abundant aquatic plants. During the day it generally lurks at the bottom, and at night it moves around foraging. It has the habit of digging burrows and making nests, does not like living in groups, and its suitable living water temperature is 15-32°C. When the water temperature is below 7°C, it is not very active and does not feed much. In pond aquaculture, mandarin fish often lie at the bottom, hiding in relatively shallow burrows.
2. Food and feeding habits of mandarin fish: A carnivorous, ferocious fish. After hatching, it begins feeding on the fry of other fish. It prefers live bait, and when hungry it will eat its own kind. At the fry stage, it can swallow fry of other cultured fish species equivalent to 70-80% of its own length. The size of the bait fish it eats depends only on what its mouth can swallow, regardless of the body length of the fish. Under artificial culture conditions, when bait types are diverse and abundant, it often chooses fish with slender bodies, soft fins and relatively small individuals as food. The maximum length of bait fish that adult mandarin fish can easily swallow is 60% of its own length, but those at 26-36% have better palatability.
3. Growth rate of mandarin fish: Under artificial culture conditions, with palatable and sufficient bait, it grows quickly. Mandarin fish raised in net cages at 1 winter of age have an average body length of 31.68 cm, equivalent to the body length of 3-winter-old mandarin fish in natural waters. Mandarin fish before 2 years of age grow faster than older fish, and 1-year-old fish grow faster than 2-year-old fish. Mandarin fish do not completely stop feeding in winter and continue to grow, but feeding intensity and growth rate slow down.
4. Pond area for culturing mandarin fish: An area of 3-5 mu is best, with a maximum of no more than 10 mu. If the pond area is too small, water quality changes quickly and is difficult to control; if the pond area is too large, bait fish are relatively dispersed, which is not conducive to mandarin fish feeding. The pond should be sheltered from the wind and facing the sun, oriented east-west, with a length-to-width ratio of 3:2, a flat bottom, sandy loam soil, and relatively little or no silt if newly excavated. The water depth should be about 1.8-2.5 m, with abundant water sources, fresh water quality, and convenient water inlet and drainage. Water from rivers, lakes and reservoirs is best, preferably with slight flow. Before mandarin fish fry and fingerlings are stocked into the pond, the pond must be thoroughly cleared and disinfected, and aerators must be installed.
5. Production of bait fish in the main culture pond: 15 days before stocking mandarin fish, put 500,000-600,000 bait fish fry per mu into the disinfected pond after toxicity has dissipated, and cultivate the bait fish in the pond to 1.2-2.0 cm per fish.
6. Timing of stocking mandarin fish fry into the pond: When the bait fish in the pond have been cultivated to 1.2-2.0 cm per fish, this is exactly the time to provide sufficient palatable early-stage bait fish after mandarin fish are stocked. Place an appropriate amount of alligator weed and water hyacinth around the pond for mandarin fish to inhabit. Thereafter, control the body length of bait fish at 1/4-1/3 of the body length of mandarin fish.
7. Stocking density and size of mandarin fish: Stock 1,000-1,200 summer fry per mu at 3-5 cm per fish.
8. Supporting production of bait fish: Under normal conditions, the bait fish in the main mandarin fish culture pond can supply mandarin fish feeding for 1 month. After 1 month of rearing, mandarin fish body length generally reaches 11.5-14 cm. In the supporting bait fish ponds (3-4 times the size of the mandarin fish culture pond), according to the requirement of a mandarin fish bait coefficient of 1:4-5, use the advantage of multiple ponds, adopt culture methods of different densities, partial harvesting in stages, and gradual thinning, and control the body length of bait fish at about 50-60% of the body length of mandarin fish in the same period, ensuring that bait fish and mandarin fish grow synchronously so that mandarin fish can feed on them.
9. Optimum growth water temperature for mandarin fish: The growth water temperature for mandarin fish is 18-30°C, and the optimum water temperature is 23-28°C. Within this range, as water temperature rises, its food intake increases and growth rate accelerates.
10. Feeding of bait fish: During the culture period, the method of feeding bait fish at intervals can be adopted according to water temperature changes. In the early and late stages, feed once every 7-10 days; in the middle stage (the high-temperature period of July, August and September), feed once every 5-7 days. Bait fish should be fed in appropriate amounts. If the density is too low, mandarin fish will consume too much energy chasing bait fish, which is unfavorable for growth; if too dense, total oxygen consumption will increase, causing mandarin fish to surface for oxygen due to hypoxia, which is unfavorable for mandarin fish growth.
11. Feeding amount of bait fish: Each feeding amount is 8-10% of the total amount of mandarin fish, maintaining the ratio of mandarin fish to bait fish at 1:5-10. After bait fish are put into the mandarin fish pond, they will still grow for some time, and a small amount of concentrated feed may be fed as appropriate.
12. Water quality management: Mandarin fish prefer fresh water quality and have relatively poor tolerance to low oxygen, so strengthening water quality management is very important. Before stocking mandarin fish fry, first drain half of the pond water, then fill with fresh water to make the pond water clear, and then stock mandarin fish fry. Mandarin fish are very sensitive to acidic water quality. From June to October, every 15-20 days or so, use 20-25 jin of quicklime per mu, dissolve it in water and splash it over the whole pond, maintaining pH at 7-8, to benefit mandarin fish feeding and growth.
13. Water addition and exchange in stages: In the initial stage of stocking, add fresh water once every 7-10 days, each time adding 10-20% of the pond water volume. By early to mid-July, gradually deepen the pond water to more than 1.5 m. From mid-July to September, as water temperature rises, generally try to exchange water once every 2 weeks, keeping water transparency at 30-40 cm. When it is less than 30 cm, exchange 1/4-1/3 of the pond water. If circulating water can be maintained frequently, so much the better, so that dissolved oxygen in the water always reaches more than 4 mg/L.
14. Turning on aerators at the proper time: During the culture process, the timing and frequency of turning on aerators should be flexibly controlled according to weather changes and water quality conditions. Turn on the aerator in time to increase oxygen during muggy weather or thunderstorms. It is also safest to turn on the aerator for two hours every midnight during the hottest summer period. Strengthen duty attendance and pond patrols. If mandarin fish are found spitting out bait fish, immediately turn on the aerator to increase oxygen and add fresh water. The timing and duration of aerator operation should be flexibly controlled according to weather and mandarin fish activity. Generally, turn it on at noon on sunny days and in the early morning on cloudy days; turn it on at midnight during continuous rainy weather; when the weather is hot, operate for a long time, and when the weather is cool, operate for a short time; when turning on at midnight, operate for a long time and only stop after sunrise in the morning; when turning on at noon, operate for a short time; when the loaded area is large, operate for a long time, and when the loaded area is small, operate for a short time. If fish are found surfacing for oxygen, turn on the aerator as early as possible. When necessary, also add or exchange fresh water. In emergency rescue, chemical oxygen-increasing agents may be used.
15. Sources of bait fish for mandarin fish: Purchase or keep domestic fish fry in dense culture and feed at any time; cultivate and collect wild trash fish fry. For every mu of mandarin fish pond, about 3 mu of bait fish nursery pond should be allocated as a companion. Carp, crucian carp, or some wild trash fish species that reproduce earlier and in larger quantities can be placed in them to reproduce large numbers of fry for mandarin fish to feed on.
16. Feeding management: Bait fish should be put in timely according to the growth of the fish and weather conditions, preferably once every 3-5 days, so that bait fish in the pond maintain a certain density. When bait sources are sufficient, as many bait fish as possible should be put in so that mandarin fish have enough food. Unconsumed feed fish can be caught together with mandarin fish at harvest and sold.
17. Aquaculture production management: Patrol the pond in the morning and evening to observe mandarin fish feeding, growth and water quality. Maintain good water quality so that dissolved oxygen in the water is above 5 mg/L. When water quality becomes too dense, flush with water in time. In hot summer weather, aerators must be used to increase oxygen. To avoid water becoming too fertile, certain aquatic plants can be cultivated in the water to purify water quality, which is beneficial to mandarin fish growth.
18. Precautions when stocking mandarin fish fry: Mandarin fish summer fry are generally stocked from late May to early June. Earlier stocking means earlier growth and earlier reaching market size. When stocking, soak the fingerlings in 30-50 g/L salt water for 10-15 minutes. Transported fingerlings must be “tempered” before stocking.
19. Early-stage bait fish cultivation: Although mandarin fish prefer clear water, it also needs some fertility. After pond clearing and 7-10 days before bait fish are stocked, apply about 600 jin of fermented organic fertilizer per mu to cultivate plankton and benthic organisms for bait fish to feed on and grow, so that mandarin fish summer fry have palatable bait as soon as they enter the pond, thereby increasing survival rate and promoting growth. 10-15 days before stocking mandarin fish summer fry, first stock fry of grass carp, bighead carp, silver carp, bream and whipfin culter in batches, 500,000-800,000 per mu. When the bait fish grow to about 1.5 cm, they are exactly the palatable bait for mandarin fish summer fry when stocked into the pond.
20. Methods for cultivating supporting bait fish: After mandarin fish begin feeding, bait fish are consumed quickly, so nearby bait ponds must be provided. They should have flat bottoms for easy netting and harvesting, and an area 3-4 times that of the main culture pond. Stock fry of species that are easy to breed, easy to catch, and favored by mandarin fish, such as blunt snout bream, silver carp and bighead carp, grass carp, and crucian carp, at 250,000-300,000 per mu. The rearing method for bait fish is the same as for conventional fish, but the size of bait fish must be well controlled to make them suitable for mandarin fish feeding.
21. Techniques for feeding bait fish: When bait fish in the pond are insufficient, supplement and feed in time. In the early stage, feed once every 4-5 days, because within 2-3 days after bait fish are put in, their activity is relatively sluggish, which is conducive to mandarin fish predation. If the interval is too long, it easily causes difficulty for mandarin fish to prey and increases energy consumption, increasing dissolved oxygen consumption in the pond. From July to September, the temperature is suitable, mandarin fish grow quickly and food intake increases, so feed once every 1-2 days. After early October, temperature drops, mandarin fish food intake decreases, and feeding amount and frequency can be gradually reduced. The feeding amount is 5-10% of the total weight of mandarin fish in the pond, increased or decreased according to mandarin fish feeding, weather, and the increase or decrease of bait fish. Never let it fluctuate abruptly. If too much, dissolved oxygen consumption in the pond increases, causing surfacing for oxygen in mild cases and pond-wide fish kills in severe cases; if too little, mandarin fish cannot get enough bait, which is unfavorable for feeding and growth, and they cannot reach commercial size in the same year.
22. Regularly check mandarin fish growth: Understand and grasp the growth, survival and standing stock of mandarin fish in the pond and the size of bait fish, adjust the feeding amount and frequency of bait fish in time, and control the size of bait fish well.
23. Precautions for water addition and exchange: In the initial stage of stocking, adding water in stages is an important measure to increase the growth rate and survival rate of mandarin fish. Because mandarin fish summer fry are delicate in constitution and weak in activity, in order to increase the density of bait fish and facilitate mandarin fish feeding, the water level should be shallower, with a water depth of 50-70 cm being best. Begin adding water about one week after stocking, then once every 4-5 days, each time adding 20-30 cm, gradually raising the water level to increase dissolved oxygen in the water and the activity space for fish. In June, maintain the water level at about 1.5 m. In July-September, water temperature is high and fish feed and grow vigorously, so flush with water 2-3 times per week, or even once daily. Exchange water once every 15-20 days, with the exchange amount at 20-30% of the pond water, maintaining pond water depth at about 2.0 m and transparency at 40-60 cm.
24. Disease prevention and control: Prevent in advance. In addition to the above-mentioned removal of pond silt, clearing the pond with quicklime, regularly splashing disinfectant drugs, and disinfecting fingerlings before stocking, also pay attention to the following:
1) Filter screens must be installed at both water inlet and outlet to prevent entry of harmful organisms. If conditions permit, water inlet disinfection is best, that is, disinfect with bleaching powder before filling.
2) Fishing gear must be disinfected. During operations, be careful and cautious, and do not injure the fish body to avoid infection by pathogens.
3) Do not use spoiled bait fish. Bait fish must be disinfected before entering the pond (commonly used drugs include salt, bleaching powder, potassium permanganate, etc.).
4) Hang drug bags in the feeding area to form medicated and non-medicated zones, so that fish self-disinfect while feeding.
25. Timely harvesting and balanced marketing: Starting in September, harvest mandarin fish that have reached commercial size, catching large ones and leaving small ones, for balanced marketing. By the end of December, drain the pond and harvest. If necessary, fish can be kept in the pond until the following spring when prices are good for marketing. Rotational harvesting and thinning can avoid concentrated marketing, reduce culture density, ease the demand for bait fish, and benefit the feeding and growth of mandarin fish remaining in the pond.