Key Technical Points and Daily Management Methods for Polyculture of Rice Field Eels and Loaches

Whether it is pond aquaculture or cage aquaculture, the following polyculture model can be adopted to increase profits.

I. Building a good aquaculture pond for polyculturing rice field eels and loaches:

Choose a location that is sheltered from the wind and faces the sun, has a quiet environment, and has convenient water sources. Cement ponds or earthen ponds can both be used, and cage polyculture can also be carried out in reservoirs, weir ponds, small ditches, and small rivers. The area is generally 25-150 sq m. If cement ponds are used to raise rice field eels and loaches, dealkalization treatment must be carried out before releasing the fry; if earthen ponds are used for aquaculture, the soil is required to be hard and the pond bottom must be tamped solid. The pond depth is 0.8-1.5 m. Whether it is a cement pond or an earthen pond, a 30 cm layer of fertile mud must be filled into the pond bottom. Fertile mud with more organic matter is best, as this helps rice field eels and loaches dig caves to live in. When building the pond, water inlets and outlets must also be set up, and the water depth should be kept at 15-20 cm. The water inlet and outlet must be tied securely with fish-blocking nets to prevent rice field eels and loaches from escaping.

About 10 days before releasing the fry, thoroughly disinfect the aquaculture pond with quicklime, and 3—4 days before releasing the fry, drain the pond water and then inject new water.

Choose polyethylene netting with fine mesh to make cages. The mesh size should be based on the principle of not letting the eels and loaches escape and facilitating water exchange inside and outside the cage. The area of a single cage should not exceed 20 sq m, and the specifications are generally 5 m-7 m long, 2 m-3 m wide, and 1.5 m-2 m high. The cages are fixed along the pond edge with bamboo poles, the cage opening is 0.5 m-0.6 m above the water surface, the distance between cages is 1.5 m, and the total cage area should not exceed 10% of the pond area. 7 days-10 days before stocking the fry, soak the new cages in water so that a layer of algae biofilm attaches to the surface of the netting, so as to avoid scratching the eels' bodies. Put soil that has been sun-dried or disinfected into the cages, about 0.2 m thick, so that the eels and loaches can burrow into the soil to overwinter in winter. Transplant water peanut inside the cages, with the coverage accounting for 70%-80% of the cage area.

II. Select good rice field eel and loach seedlings and stock them reasonably:

Whether rice field eel and loach aquaculture succeeds depends on the seedlings. For rice field eel seedlings, it is best to use artificially bred and domesticated dark yellow large-spot rice field eels or golden yellow small-spot rice field eels. Variegated eel seedlings and eel seedlings that have not undergone domestication must not be used. The size of rice field eel seedlings is preferably 50-80 per kg. If too small, feeding is poor and the survival rate is also low. The stocking density is generally preferably 1-1.5 kg of eel seedlings per sq m. After the rice field eels have been stocked for 20 days, release loach seedlings at a ratio of 1:10. For loaches, it is best to use artificially bred ones, which have a high survival rate.

Before stocking eel and loach seedlings in the pond, stock seedlings according to conventional aquaculture requirements. Eel and loach seedlings can be stocked from April to November. The specification of eel seedlings is about 20 g each. Rice field eels in the same cage should be as uniform in size as possible to avoid eating each other. Stock as early as possible to help improve the out-of-cage specification. For each sq m of cage, stock 2 kg of rice field eels with a specification of 25 g and 0.5 kg of loaches; or stock 3-4 kg of rice field eels with a specification of 50 g and 1 kg of loaches. 3-5 days before stocking the seedlings, disinfect the water peanut and water body with bleaching powder aqueous solution. For disinfection of eel and loach seedlings, soak in 10 ppm methylene blue aqueous solution for 10-15 [minutes], or bathe in 20 ppm potassium permanganate aqueous solution for 5-10 minutes, or soak in 3%-4% salt water solution for 3-5 minutes.

III. Feeding compound feed:

First install feeding tables. The feeding tables can be made of wooden boards or plastic boards, and the area can be determined according to the size of the pond, 5 cm below the water surface. Do not feed during the first 3 days after stocking rice field eel seedlings, so that the rice field eels can adapt to the environment. Start feeding feed from the fourth day. Feeding at around 7 p.m. every day is best, as the rice field eels' feed intake is highest at this time. Artificial rearing of rice field eels mainly uses compound feed, with appropriate feeding of some live feeds such as small fish, small shrimp, earthworms, fly maggots, river snails, yellow mealworms, silkworm pupae, pig blood, and animal viscera. For artificially domesticated rice field eels, compound feed and earthworms are their favorite feeds. Using artificially bred dark yellow large-spot rice field eel seedlings and feeding compound feed, the daily feeding amount is 3%-5% of the rice field eels' body weight, fed 1-2 times per day (depending on weather and water temperature), following the principle of fixed time and fixed amount. Raising 20 g rice field eel seedlings can grow to 200-300 g in one year. Loaches in the pond mainly feed on the feces excreted by the rice field eels and the unfinished rice field eel feed. Part of this can also be solved by fertilizing the water quality. Loaches reproduce quickly naturally. When the proportion of loaches in the pond is greater than 1:10, feeding bran once a day is sufficient. The feeding amount should be small at first and then gradually increased.

When artificially culturing rice field eels, it is best to stock a certain proportion of loaches after the feeding training work is completed, so as to achieve mutually beneficial coexistence of rice field eels and loaches and create good economic benefits. This is because loaches and rice field eels have different feeding habits and different abilities to accept compound feed. Loaches can almost adapt without feeding training, while rice field eels need a period of compulsory feeding training to adapt. During feeding training, it is often the case that before the rice field eels have opened their mouths to feed, the loaches have already eaten it all, thereby affecting the rice field eels' feeding training time and even causing the feeding training to fail. Loaches are active and dart up and down when feeding, causing greater water fluctuations, so that part of the feed is lost into the water, polluting the water quality, affecting the utilization rate of the compound feed, and thus prolonging the feeding training time.

IV. Rearing management

The growing season for rice field eels and loaches is April-November, with the peak season from May-September. During this period, management should be "diligent" and "careful," that is, frequent pond patrols, frequent management, and timely solving of problems when found. Persist in checking the cages morning and evening, prevent escape, prevent rats, prevent theft, and prevent flooding, and promptly remove water peanut that grows too vigorously in the cages to prevent it from growing outside the cages and causing the eels and loaches to escape. After November, for cages without a soil layer, the water peanut can be thickened to 0.3 m and then pressed down with heavy objects, allowing the eels and loaches to hide in it to overwinter. Carefully observe the growth status of rice field eels and loaches in the pond so as to take corresponding measures in time. The habit of rice field eels and loaches is to hide by day and come out at night. Keep the pond water fresh and clear, with a pH value between 6.5—7.5, and an appropriate water level.

V. Prevention is the main approach for eel diseases

Frequently splash the whole pond with 1—2 ppm bleaching powder, and regularly use copper sulfate medicine to prevent diseases. Because once rice field eels become diseased, the treatment effect is relatively poor, so prevention is more important than treatment.

Analysis of the advantages and disadvantages of polyculture of rice field eels and loaches

In artificial eel culture, whether pond aquaculture or cage aquaculture, when stocking eel seedlings, pairing with a certain proportion of loaches is very beneficial. This is because:

1. Rice field eels and loaches have different feeding habits, and the two can fully utilize different bait resources in the water area. The polycultured loaches can also feed on the residual bait left by the rice field eels, reducing feed loss and waste. This can not only help prevent water quality deterioration, but also harvest a certain number of loaches, increasing economic income.

2. Loaches are more active than rice field eels and often dart up and down. Their active habit can prevent rice field eels from tangling with each other due to excessive density, thereby maintaining the normal mucus on the body surface of the rice field eels and reducing the occurrence of eel diseases; moreover, the up-and-down movement of the loaches increases the dissolved oxygen in the water, creating a good living environment for the rice field eels.

But now artificial eel culture mostly uses compound feed, so feeding training is needed, and polyculturing loaches during feeding training is unfavorable:

1. Because loaches and rice field eels have different feeding habits, their abilities to accept compound feed differ. Loaches can almost adapt without feeding training, while rice field eels need a period of compulsory feeding training to adapt. During feeding training, it is often the case that before the rice field eels have opened their mouths to feed, the loaches have already eaten it all, thereby affecting the rice field eels' feeding training time and even causing the feeding training to fail.

2. Loaches are active and dart up and down when feeding, causing greater water fluctuations, so that part of the feed is lost into the water, polluting the water quality, affecting the utilization rate of the compound feed, and thus prolonging the feeding training time. Therefore, when artificially culturing rice field eels, it is best to stock a certain proportion of loaches after the feeding training work is completed, so as to achieve mutually beneficial coexistence of rice field eels and loaches and create good economic benefits.

Benefits of polyculture of rice field eels and loaches

1. Bait can be fully utilized. Rice field eels are partial to animal bait, while loaches are omnivorous fish. When young, they feed on small crustaceans, aquatic earthworms, and aquatic insects, and when adult, they mainly switch to plant-based bait, and sometimes also eat bottom humus. Polyculture with rice field eels does not occupy additional bait and can eat the residual bait left by the rice field eels, which can not only fully utilize the bait but also help prevent water quality deterioration.

2. Improve the living environment and prevent fish diseases. Loaches are good at darting up and downstream, loosening the soil, which is beneficial to the reproduction and growth of aquatic organisms in the bottom mud, adding bait for rice field eels and favoring their growth. Loaches are very active and can dissolve supersaturated oxygen from the upper layer of the field into the lower water, creating a good living environment for rice field eels.

3. Prevent rice field eels from tangling and fighting with each other. Raising rice field eels together with loaches can also prevent rice field eels from tangling and fighting with each other, which not only prevents rice field eels from being injured but also reduces the occurrence of diseases.