Wild capture methods, living habits and artificial breeding techniques of the rice field eel (Monopterus albus)
Living habits of the rice field eel:
(1) Burrowing behavior (habitation).The rice field eel is a bottom-dwelling fish that lives in freshwater. It requires a relatively stable living environment and prefers to inhabit places with dim light, small water temperature fluctuations and little human disturbance. It likes to live in soft, humus-rich shallow water and still-water mud, burrowing about 30 cm below the ground surface. The eel likes to bore into holes to live; it burrows directly without pushing the soil outward. The burrow has two or even more openings, and there is another one used exclusively for reproduction, called the breeding hole, which is wider and more concealed. The burrowing behavior of the rice field eel changes with temperature and water level, and also differs among different regions and different sizes of eel.
Whichever breeding method is adopted, such as net cages, courtyard ponds, industrial farming, and soil-based or soil-less farming, the breeding water level should be shallow, and fish nests or aquatic plants should be provided. Experiments have found that although eels without nests eat more, they move around a lot and consume more energy; the opposite is true with nests. Therefore, it is best to adopt a semi-shaded healthy breeding method, so that the eels eat more and consume less, thereby rapidly gaining weight and improving breeding efficiency.
(2) Sex reversal.The rice field eel has the trait of sex reversal, being female first and male later in life. From the embryo to the sexually mature stage, that is, at 1 to 2 winters of age and with a body length under 30 cm, the eel is generally female. After the female eel spawns, it enters the intersex stage, during which the eel has no reproductive capacity and its sex is difficult to distinguish. With increasing age and body length, the female ovary gradually changes into a testis, transitioning to male. Eels with a body length above 50 cm are generally male, and remain male for life.
Sex reversal in the rice field eel is affected by nutrition; when food is scarce, sex reversal occurs earlier. During the breeding period of female eels, feed with high calories, high protein and high vitamins should be given, which is beneficial to the reproduction and growth of the eels. Because the growth rate of male eels is more than 2 times that of female eels, when necessary, making the eels male and skipping the breeding period can increase economic returns.
(3) Food preference.The rice field eel is a typical fierce fish that feeds mainly on meat. It has a large and greedy appetite, with a daily food intake of 5% to 10% of its body weight. The eel can also endure hunger; it will not die even after going without food for a long time, but its body becomes thin, its resistance decreases and it is prone to disease. The eel prefers live bait and will not eat food that is unpalatable or rotten and spoiled. It most likes small fish, small shrimp and the larvae of aquatic insects, followed by terrestrial insects and earthworms; it also very much likes river mussels and river snails after their shells are removed. The eel feeds by a sucking-and-drawing method rarely seen among fish, rapidly striking and swallowing prey within its effective range. If a certain bait has been fed for a long time, it is relatively difficult to change its feeding habit, so wild eels should be trained to accept bait within a short period. Based on this characteristic, an artificial compound feed that can be fed for the long term, has low cost and gives a high meat gain rate should be selected. Where conditions permit, lights can be set up over the pond to attract insects into the pond for the eels to eat.
(4) Gregariousness.The rice field eel likes to gather in groups and can gather and separate, especially the small individuals. This is mainly to gain more strength to adapt to and adjust to the living environment. Eels that often live alone or do not burrow are mostly abnormal.