Five key gates to get right in pond-based monoculture of mandarin fish
In recent years, artificial farming of mandarin fish in China has developed rapidly. The author has also been engaged in pond-based monoculture of mandarin fish for many consecutive years since 2003 and has achieved certain results. The production experience of recent years is summarized below to share with fellow aquaculture colleagues.
1. Strictly control the gate of pond farming conditions.
Monoculture ponds for mandarin fish require a flat bottom, with sediment less than 15cm. Sandy-bottom ponds and newly dug ponds give better results for farming mandarin fish. Ponds are mostly 3-5 mu, which is suitable. If the pond area is too large, it is unfavorable for mandarin fish to prey; if the area is too small, the pond water quality is not easy to control, and it is prone to oxygen deficiency and pond turnover, with greater risk. Because mandarin fish like fresh water with high dissolved oxygen, the monoculture pond must have sufficient water source, convenient water intake and drainage, and the normal water storage depth must not be less than 2m.
2. Strictly control the gate of fingerling stocking.
Fingerling stocking density should be determined according to water quality, the abundance or shortage of forage fish, climate, and management level. Generally, in the Yangtze River basin, in early June each year, 800-1,000 mandarin fish fry of 4-5cm can be stocked per mu; alternatively, through 20-25d of concentrated intensive rearing, 4-5cm mandarin fish fry can be raised to about 10cm and then put into ponds. For this size of fingerling, 500-800 can be stocked per mu, which can greatly increase the survival rate of farming.
3. Strictly control the gate of forage fish feeding.
Mandarin fish feed on fish and shrimp throughout their lives. The species, size, and quantity of forage fish all have a great influence on the growth of mandarin fish.
According to the author's observations over many years, among different species and the same size of forage fish, mandarin fish most prefer to prey on topmouth gudgeon and mud carp, followed by bream and grass carp, and then crucian carp, bighead carp, silver carp, etc. Generally, the size of forage fish fed should be 1/3-1/2 of the body length of the mandarin fish. If the forage fish are too small, it is unfavorable for the growth of mandarin fish; if the forage fish are too large, after the mandarin fish feeds hungrily, it may choke the mandarin fish to death, or it may injure the digestive tract of the mandarin fish and cause infection.
To ensure the supply of forage fish, the area of the mandarin fish monoculture pond and the forage fish pond should be matched at 1:3. Among this, the matching method for forage fish in the early stage of farming is: use the idle time before stocking mandarin fish to cultivate early-stage forage fish in the pond, that is, 15-20d before stocking mandarin fish fingerlings, put 400,000-500,000 forage fish fry per mu, and conventional methods can be used for rearing. The matching method for forage fish in the middle and late stages of farming is: adopt multi-pond, high-density rearing, stock fully at one time, harvest in batches, and gradually thin out the stock, ensuring that forage fish and mandarin fish grow synchronously. Usually, by this method, 30,000-50,000 fry can be stocked per mu of water surface. Forage fish are cultivated by combining fertilization and feeding commercial feed.
To make full use of the forage, feeding of forage fish must be scientifically arranged, and the feeding amount must be moderate. In the early stage, feed once every 5-7d; in the high-temperature season from July to September, feed once every 3-5d. The daily food intake of mandarin fish is related to the season. From June to July, the feeding amount is 15%-20% of the body weight of the mandarin fish; from August to September, it is 10%-15%; from October to November, it is 5%-10%; in winter, feeding does not stop completely. If too much forage fish is fed each time, it will increase the total oxygen consumption of the farming water body and cause oxygen deficiency; if too little forage fish is fed each time, mandarin fish will consume too much energy in predation, which is unfavorable for growth.
4. Strictly control the gate of water quality management.
Mandarin fish have relatively high requirements for the farming water body, so water should be added frequently, changed frequently, and oxygenated frequently. If early-stage forage fish have already been cultivated in the mandarin fish monoculture pond, before the mandarin fish fry are put into the pond, part of the old water should be replaced to improve the current situation of excessively fertile water caused by cultivating forage fish.
Generally speaking, in the early stage of mandarin fish monoculture, the water level should be shallow, about 70-80cm, which is favorable for mandarin fish to prey and can increase the survival rate of farming. After 1 week of farming, begin adding water, and thereafter add water once every 5-7d, 20-30cm each time. In the high-temperature season from July to September, flush water once every 3-5d, and change water about once every 15d, with the water exchange volume about 20%-30% of the pond water. To increase dissolved oxygen in the water body, reduce the feed coefficient, and accelerate material circulation in the water environment, turn on the aerator at appropriate times. Usually, turn it on at noon on sunny days, in the early morning on cloudy days, and in the middle of the night during continuous rain. Make sure that on hot days the running time is long, and on cool days the running time is short; the running time in the middle of the night is long, and the running time at noon is short. In addition, mandarin fish are relatively sensitive to acidic water bodies. About once every 20d, spread 15kg of quicklime per mu of water surface.
5. Strictly control the gate of disease prevention and control.
We must adhere to “prevention first, combining prevention and control” and eliminate disease-causing hidden dangers to the greatest extent. To this end, first, do a good job of pond disinfection. Where conditions permit, expose the pond to the sun, or refer to conventional methods and spread quicklime over the whole pond for disinfection per mu of water surface. Second, disinfect fingerlings before they are put into the pond. Usually, before robust fingerlings are put into the pond, soak them in 3%-5% salt water for 3-5min. Third, disinfect forage fish. To prevent disease from entering through the mouth and pathogens from being carried out, all forage fish fed must be disinfected. In seasons with a high incidence of bacterial diseases, forage fish are usually soaked in 10ppm bleaching powder solution for 10min; in seasons with a high incidence of parasitic diseases, forage fish are soaked in 3%-5% salt water for 3-5min, or soaked in 8ppm CuSO4 solution for 10min. Fourth, disinfect tools. Wash and sun-dry fishery tools frequently, and when necessary soak them in CuSO4 or bleaching powder solution for disinfection to kill harmful pathogens. Fifth, ecological prevention and control. Regularly spread biological fertilizer to keep the water environment in the best condition. Sixth, regular prevention. Alternately use CuSO4 and FeSO4 mixture (0.7ppm), bleaching powder (1.2ppm), and Sandai Xia'an (0.1ppm), spreading once every 15-20d to kill pathogenic bacteria in the water body and cut off the transmission routes of pathogens. Seventh, correctly select drugs and apply the right medicine for the disease. For bacterial gill rot, 0.4-0.5ppm of trichloroisocyanuric acid with 85% available chlorine can be spread over the whole pond; for trichodiniasis and chilodonelliasis, 0.7ppm of CuSO4 and FeSO4 mixture can be spread over the whole pond; for Sinergasilus disease, 2.5% trichlorfon powder combined with FeSO4 at 1.4ppm can be spread over the whole pond; for hemorrhagic disease, Sandai Xia'an at 0.1ppm can be spread over the whole pond.