How can freshwater pomfret be farmed for rapid grow-out?
From May to November 2009, 5 recreational fishing farms in Yuetang District, Xiangtan, adopted the 80:20 high-efficiency adult fish pond farming model for freshwater pomfret, that is, in pond farming the main cultured species is freshwater pomfret (a feeding fish) at 80%, with accompanying fish (filter-feeding fish) at 20%, mainly feeding a complete extruded pellet feed. Freshwater pomfret were stocked from May 6 to 10, when the water temperature was stable above 20°C. Silver carp and bighead carp were stocked in early to mid-April. Before stocking, the fish bodies were disinfected. As for the stocking situation, freshwater pomfret accounted for 80.5%-89.5% of the total number stocked, and silver carp and bighead carp accounted for 10.5%-19.5%. The fingerling size was 8-15 g per freshwater pomfret, while the silver carp and bighead carp fingerlings were self-bred large-size fingerlings. The feed was a special extruded pellet compound feed for freshwater pomfret, with protein content >32%, crude fat >4.5%, and crude fiber <6%. In 2009, the 5 farms together developed 3.0 hm2 of water surface for pomfret farming. At harvest, the average yield per mu was 752 kg, freshwater pomfret accounted for 81.3%-88.6% of total output, and the survival rate was 98%. After about 80 days of feeding, by the end of July the pomfret could reach market size (over 500 g per fish), going to market 1 month earlier than with ordinary farming methods. At this time, partial harvesting or harvesting through angling could be carried out, and the market price was high, thereby improving economic returns. The 5 farms achieved an average net profit of 8,000 yuan per mu, with an input-output ratio of 1:2.56, giving very good benefits. The main techniques are summarized below.
Main measures of freshwater pomfret farming techniques
1. Pond conditions
The area of adult fish ponds should preferably be 0.2-0.6 hm2, with a water depth of about 1.2 m, fresh water quality, transparency of 25-40 cm, a relatively flat pond bottom, and about 10 cm of pond bottom silt, with convenient drainage and irrigation. It is best to equip 0.2-0.3 kw of aerator per mu, and pond clearing and disinfection must be carried out before stocking fingerlings.
2. Fry and fingerling stocking
The freshwater pomfret fingerlings stocked should be uniform in size, robust in constitution, and free of disease and injury. When the fingerlings enter the pond, operations should be careful to avoid injuring the fish bodies, and 3-4% salt should be used for disinfection. For fingerlings that have undergone long-distance transport, before entering the pond they should first be kept temporarily in a net cage for a period, and after the fingerlings have recovered slightly, disinfection treatment should then be carried out. The stocking density of fingerlings is generally 1,000-1,100 fish per mu for 8-15 g fingerlings; other fish species can be polycultured in combination, with the accompanying species being 50 silver carp and 50 bighead carp, each weighing 100-150 g.
3. Bait and feeding
1) In ponds where freshwater pomfret are mainly cultured, feeding should be based mainly on a complete extruded pellet feed, and feeding technique is related to fish yield, market fish size, fish farming cost, and economic returns. Freshwater pomfret is a fish that constantly searches for food, and its intestine is short, so digestion and absorption are fast. Therefore, it needs to be fed many times. The number of feedings is 4 times per day, 2 times in the morning and 2 times in the afternoon, with the morning feeding amount accounting for 40% and the afternoon accounting for 60%. A reference formula for the compound feed is: fish meal 5%, soybean cake 20%, rapeseed cake 30%, rice bran 15%, wheat bran 8%, flour 15%, corn 10%, mineral premix 2%. Generally, the daily feeding rate of compound pellet feed for freshwater pomfret is 3%-6%. Freshwater pomfret feeding requires feed training. This fish is easy to train to gather and rise to the surface to compete for food; train it 3 times per day, 30 min each time, and generally within 5 d it can be trained to feed at a fixed point at the feeding platform;
2) The amount of base fertilizer applied to the pond is the same as for ponds mainly culturing the four major Chinese carps. Before stocking fingerlings, apply 200 kg of fermented manure per mu as base fertilizer, and during the rearing period apply a small amount of additional fertilizer 3-4 times depending on water quality, 50 kg each time;
3) Use black light lamps to attract insects to feed the fish. The working principle of a black light lamp is the same as that of an ordinary fluorescent lamp, consisting of a ballast, a starter, and a lamp tube, except that the lamp tube does not emit incandescent light, but a kind of light that has an attracting effect on flying insects. Simply set up the black light lamp 50 cm above the water surface, connect the power, and turn it on at night. Flying insects within a 5 m radius around the lamp, especially moths, will fly toward the lamp and fall into the fish pond below the lamp, where they are just eaten by the freshwater pomfret, with particularly good results. For every 10 h turned on (that is, one night), the electricity cost is 0.1 yuan, but the flying insects attracted can reach several kg, or even several tens of kg, greatly reducing the feed cost for freshwater pomfret.
4) Broaden feed sources and add some animal offal to feed the fish. Freshwater pomfret is an omnivorous fish with a relatively broad diet, and farmers can use the offal of poultry and livestock from slaughterhouses to feed freshwater pomfret. On the one hand, freshwater pomfret likes it very much; on the other hand, when fed with poultry and livestock offal, freshwater pomfret grows relatively fast. Poultry and livestock offal is low in price and easy to obtain, and can greatly reduce feed costs. Freshwater pomfret also very much likes to eat river snails, freshwater mussels, and earthworm meat, and farmers can use free time to obtain these very easily available natural feeds to feed freshwater pomfret, or they can raise some river snails, freshwater mussels, and earthworms for freshwater pomfret to use. In terms of plant-based feed, idle land can be used to grow green feeds such as ryegrass and Sudan grass. Using idle water surfaces to grow small duckweed to feed freshwater pomfret also gives quite good results.
4. Daily management
1) Persist in frequent pond patrols and observe changes in water quality. In summer, add fresh water once every 3-5 d; in autumn, add fresh water once every 7-10 d. On sunny days at noon, turn on the aerator for 1-2 h to increase dissolved oxygen in the water; in rainy or stuffy weather, once fish are found floating at the surface, promptly turn on the aerator or add fresh water. Although freshwater pomfret tolerates low oxygen, when dissolved oxygen in the water falls below a certain threshold it will also float at the surface, or even cause a pond-wide fish kill. As long as freshwater pomfret floats at the surface once, it will not feed or will feed very little for 3-4 d, and it takes 5-6 d to return to normal. During these 5-6 d it not only does not grow, but also consumes energy; that is, each surface-floating event equals 10 d without growth. Therefore, water quality management is crucial during the farming process. Fresh water should be replenished in time, transparency should be kept at about 25 cm, and mechanical aeration measures should be taken when necessary.
2) Disease prevention work should be done well. May to September is the disease outbreak season for freshwater pomfret. Like for the four major Chinese carps, quicklime or bleaching powder should be used regularly to disinfect the pond water to prevent fish diseases. In addition, floating aquatic plants such as duckweed can be grown at the edge of the fish pond, which can serve as fish feed, also serve as shade for fish in high-temperature seasons, and can increase dissolved oxygen in the water, prevent the water from becoming too fertile, and regulate water quality.
5. Disease treatment techniques
Freshwater pomfret has strong disease resistance. When the water temperature is above 26°C, the survival rate is generally above 90%. When the water temperature is 15-20°C, young fish are prone to ichthyophthiriasis, white skin disease, and dactylogyrosis. During the overwintering period, freshwater pomfret is also prone to saprolegniasis, water mold disease, and trichodiniasis.
1) Ichthyophthiriasis: The pathogen is the larva or adult of Ichthyophthirius multifiliis. A large amount of mucus appears on the body surface of diseased fish, and in severe infections it appears cloud-white in the water. At the same time, there is congestion at the base of the dorsal fin and caudal fin. Prevention and treatment methods: first, raise the water temperature as much as possible; second, use 2.5 kg of crushed red chili pepper per mu of water surface, boil it, and splash it over the whole pond.
2) White skin disease: The pathogen is Pseudomonas dermoalba. At first, the body surface, dorsal fin, caudal fin, and forehead of diseased fish turn slightly white, and at the whitened areas the scales fall off at a touch. In severe cases, the fish body loses balance, spins in the water, moves slowly, or hangs at the water surface with head up and tail down. The time from onset to death is short, and the mortality rate within 3 d can reach more than 60%. Prevention and treatment methods: first, splash the whole pond with a bleaching powder solution at a concentration of 1 mg/L, once a day for 3 consecutive days. Second, soak diseased fish in an oxytetracycline solution at a concentration of 25 mg/L for 30 min.
3) Saprolegniasis: The pathogen is bacteria. The skin of diseased fish becomes inflamed, and in severe cases the scales fall off, the muscles rot, and round lesions form; the fish swims slowly, loses balance, and soon dies. The prevention and treatment method is to splash the whole pond with a bleaching powder solution at a concentration of 1 mg/L.
4) Water mold disease: The pathogen is water mold. The body surface of diseased fish has clustered hyphae, movement is sluggish, tissues necrose, and soon the fish loses balance and dies. The prevention and treatment method is, at the time of onset, to splash the whole pond with a methylene blue solution at a concentration of 0.1 mg/L, once a day for 3 consecutive days.
5) Dactylogyrosis: The pathogen is Dactylogyrus. Because the gills are irritated, diseased fish are extremely restless, either swimming wildly at the water surface or rapidly swimming on their sides at the bottom, with poor appetite, and the fish body gradually becomes emaciated and dies. The prevention and treatment method is to soak diseased fish in a potassium permanganate solution at a concentration of 20 mg/L for 20-30 min. Or splash the whole pond with a mixture of a copper sulfate solution at a concentration of 0.5 mg/L plus a ferrous sulfate solution at 0.2 mg/L.
6) Trichodiniasis: The pathogen is Trichodina. Disease occurs only after the fish body is parasitized by a large number of Trichodina. The prevention and treatment method is to splash the whole pond with a mixture of copper sulfate and ferrous sulfate (5:2) at 0.7-1 mg/L.