Detailed Explanation of Key Technical Points for Eel Farming in Earthen Ponds
Eel, also known as white eel, white loach, etc., is a valuable fish species for freshwater aquaculture. Its flesh is tender, its flavor delicious, and its nutritional value high; it has medicinal effects such as removing blood stasis and promoting tissue regeneration, and nourishing and tonifying the body. Eel grows rapidly and has strong adaptability; even in waters with very little dissolved oxygen where other fish cannot survive, it can live normally. The technical requirements for artificial farming are not high, and feed sources are also plentiful. In recent years, farmers have extensively raised eel in earthen ponds, all achieving high yield and high efficiency. Eel fry stocked in early spring can be marketed by late autumn and early winter, generally yielding 800 kg to 1000 kg per mu. The secrets of high-yield and high-efficiency eel farming in earthen ponds are introduced as follows:
I. Pond Selection and Disinfection
Earthen ponds for eel farming require good ventilation and sun exposure, and sufficient water sources; the area should not be too large. Around the earthen pond, plant water hyacinth or alligator weed, etc., in a 0.8 m to 1 m wide strip, and enclose it with a fence or mesh; this can both prevent eels from escaping and provide shade, favoring their growth.
Before stocking, excess mud should be dug out from the soil, the pond bottom leveled, the pond embankments and the inlet and outlet repaired. 10 to 15 days before the eel fry are put into the pond, disinfection should be carried out at 100 kg to 125 kg of quicklime per 1000 sq m to thoroughly kill wild trash fish and harmful organisms. Then, 5 to 7 days before the eel fry are put into the pond, fill with water to a depth of 0.6 m to 0.7 m, filtering the inlet with a 60-mesh sieve. Finally, apply base fertilizer; generally, spread 300 kg to 400 kg of decomposed pig or cattle manure per 1000 sq m, and wait until the water turns light green or yellow-brown before releasing the eel fry, so that after entering the pond they can eat sufficient natural food. After about 15 days, deepen the pond water to 1.5 m.
II. Eel Fry Treatment and Stocking
The suitable temperature for eel growth is 20°C to 28°C; they begin feeding at a water temperature of 12°C, so the stocking time is generally from late February to mid-March. Before stocking, first soak the eel fry packaging bags in water for 20 to 30 minutes to adapt to the water temperature; only when the temperature difference inside and outside the bag is less than 5°C can the bags be opened. Then pour 2 to 3 basins of pond water into the bag with a small basin, so that the eel fry gradually adapt from a high-dissolved-oxygen state to a low-dissolved-oxygen state. At the same time, before stocking, the eel fry should also be disinfected: soak the eel fry in 0.75 kg to 1 kg of table salt per 50 kg of water for 15 to 20 minutes.
The eel fry to be stocked should have a blue-gray body color, plump and moist skin, good elasticity, and active swimming. The size of eel fry in the same pond should be uniform and consistent; otherwise, competition for food among eels will affect the food intake of the weaker individuals. The stocking density is generally 4000 to 5000 eels of about 20 g per 1000 sq m; 3000 to 4000 of about 50 g; and 2000 to 3000 of about 100 g. At the same time, each 1000 sq m earthen pond can be polycultured with 50 bighead carp, 30 silver carp, and 200 tilapia; on the one hand, they can filter-feed on plankton and consume the feces excreted by the eels, thereby purifying the water quality; on the other hand, they can increase fish yield.
III. Feed Types and Feeding
Artificial eel farming mainly relies on special compound feed (available on the market), and in each 50 kg of special feed, add 50 g to 60 g of multivitamins (vitamins a, b, c, e) and 1.5 kg to 2 kg of cod liver oil (when the water temperature is below 20°C or above 35°C, cod liver oil should be withheld). For young eels, add slightly less; for adult eels, add more. If special feed is temporarily unavailable, small trash fish, livestock and poultry viscera, silkworm pupae, and other animal feed can be minced and mixed with flour as a substitute; its crude protein content must be above 40%.
Eel is a carnivorous fish and is greedy for food. When feeding, the “four fixeds” principle should be implemented, namely fixed quality, fixed quantity, fixed time, and fixed location. Fixed quality: ensure the quality of the feed. The prepared feed should be moderately soft and hard (water addition is 1.2 to 1.3 times), fresh and clean, and must not deteriorate or rot. Fixed quantity: the feeding amount should be appropriately adjusted according to the size of the eels, food intake, digestion, and the weather, water temperature, and water quality conditions. Generally, the daily feeding amount is 1.5% to 2.5% of the eel body weight, and it is best if consumed within 12 hours. Fixed time: for small fish size and high density, feed once each at about 8 a.m. and 4 p.m. daily; for eels over 100 g, feeding once daily at 8 a.m. to 9 a.m. is sufficient. Fixed location: feed is placed on fixed feeding platforms; each 1000 sq m earthen pond can be provided with 2 to 3 feeding platforms.
IV. Daily Management and Disease Prevention
Patrol the pond every morning and evening to observe the eels' activity and feeding conditions, and check the drainage outlet after rain to prevent fish from escaping. Normally, add fresh water once every 10 to 15 days; in summer and autumn, once every 5 to 7 days, each time exchanging about 10% of the whole pond. At the same time, keep the ph value between 7 and 8.5; when the ph value is too high, replace with fresh water, and when too low, adjust with 15 kg to 20 kg of quicklime per 1000 sq m.