Detailed Explanation of Key Points of Leech Cage Culture Technology
When you see leeches in rural villages, they grow in muddy fields; those are wild leeches. Now, with artificial breeding, many are raised in ponds, cages, and rice fields. Follow the editor to see how they are raised in cages.
Leech cage culture technology
1. Cage setup
The fish ponds each have an area of 1000 sq m, longer east-west and wider north-south, with a flat pond bottom free of silt, convenient water inlet and drainage, and a year-round water level no lower than 1.0 m. In the pond, they are arranged in multiple rows in parallel and staggered, with 2 m between each row, no gap between cages within a row, and more than 1.5 m from the pond ridge. In each fish pond, 10 rows of 50 cages are set up, with the cage submerged to a depth of 0.2 m, exposed above water by 0.8 m, and the cage bottom about 0.2 m above the pond bottom.
The cage is a rectangular open-top cage made of polyethylene knotless netting, with an anti-escape lip extending inward 0.15 m around the upper opening. It is fixed around with wooden stakes, and the upper end is tightened with soft steel wire rope.
2. Preparatory work before entering the cages
The juvenile leech cages are disinfected by splashing the whole pond with 250 ml of 10% povidone-iodine, and after 24 hours, 1 kg of biological fish fertilizer is applied.
3. Juvenile leeches entering the cages
After all preparatory work is done, 20 jin of leech egg cocoons that had been incubated for 20 days in soil in foam boxes and, after being cleaned, were about to hatch are placed in. In the 20 juvenile leech cages, about 400 egg cocoons per cage, about one jin, are stocked, then 2 foam box lids are placed in each cage; on the 10th day, 2-3 inch-long loaches and 4-5 summer grass carp are placed in.
4. Covering with bird-proof netting
On the second day after the leech egg cocoons enter the cages, polyethylene netting cut to a specification of 20.5 m×2.05 m with a mesh of 5 cm is covered over 4 rows of five cages arranged longitudinally to prevent bird damage, and a net needle is used to sew and fix the bird-proof net onto the cages at a standard of 1 knot per 1 m.
5. Feeding management
① Baiting: In the juvenile leech cages, Radix snail is fed. The snails are soaked for 8 hours in a multivitamin solution, and thereafter fed once every three days. The feeding amount is adjusted and supplemented according to how many floating snails remain in the cage.
After cage splitting, the feed is changed to fresh live river snails taken from the lake area. At different growth stages of the leeches, steel sieves of different specifications, 0.8×0.8 cm, 1.2×1.2 cm and 1.6×1.6 cm, are used to remove the large and keep the small for supplementary feeding.
② Water quality adjustment: Biological fertilizer is applied, with amounts of 0.7 kg and 5 kg per mu per meter of water depth respectively. After the fertilizer is diluted, it is splashed at a dosage of 2/3 inside the cage and 1/3 outside the cage; in addition, 20 ml of EM bacterial agent water conditioner and 10 g of Youdi bacteria are put into each cage every fifteen days.
As the leeches grow, the water level is gradually deepened until the cage is submerged to a depth of 0.5 m; in July, August, September and October, a 5-inch submersible pump is started at noon every day to pump water for two hours, so that the pond water flows and circulates as a whole through the culvert between the two fish ponds. Throughout the leech culture period, the water transparency is always kept between 20-30 cm.
③ Leech disease prevention: Throughout the entire culture process, adhere to the principle of “prevent disease before it occurs, treat disease early when it occurs.”
④ Leech cage splitting: When each 0.5 kg of leeches reaches 1000 individuals, the juvenile leeches from the 20 cages are separately put into 100 young leech cages at a standard of one and a half jin of leeches per cage. The next day, after 2-3 inch-long loaches and 4-5 summer grass carp fingerlings are evenly placed in the cages, all are covered with bird-proof netting.
⑤ Daily management: Patrol the pond once a day, check whether the cages are damaged and the feeding situation of the leeches, observe the living and growth dynamics of the leeches, and keep various production records.
Distribution
They are produced in lakes, ponds and rice fields in most areas of China. Jinqian leeches are mainly produced in Weishan Lake, Dongping Lake, Nanyang Lake and other lakes, with Weishan Lake having the largest output; besides supplying the province, they are also sold to Northeast China, Hebei and Shanxi. A portion of the output from the suburbs of Suzhou, Wu County and other places in Jiangsu is also sold elsewhere. In addition, they are also produced in Zhejiang, Hunan, Hubei, Shaanxi, Liaoning, Anhui, Hebei, Sichuan, Jilin, Heilongjiang and other places, all for local production and local sales.
Living environment
Leeches are omnivorous animals. Their main way of life is sucking animal blood or body fluids. They often use aquatic plankton, insects and mollusks as their main bait. Under artificial conditions, various animal internal organs, cooked egg yolks, compound feed, plant residues, freshwater snails and shellfish, miscellaneous fish, earthworms and so on are used as bait.
They live in rice fields, ditches, shallow polluted ponds and other places, are fond of sucking human and livestock blood, move very quickly, can swim in waves, and can also move in a looper-like manner. Whenever spring warms, they become active. June to October is their egg-laying period. In winter they often lie dormant in wet mud near the shore, not eating or moving, with strong survival ability.
Growth and reproduction
Reproductive habits: Leeches are hermaphroditic, mate with different individuals, and fertilize internally. They possess both female and male reproductive organs at the same time. During mating, they proceed in opposite directions to each other. In their life history there is a phenomenon of “sex reversal”; there is an exchange of gender roles. A single leech can be both a father and a mother, playing different roles at different periods of its life. About one month after mating, the female reproductive organ secretes a thin mucus, which encloses the egg band, shaped like a “silkworm cocoon”, and is discharged from the body. It hatches in wet mud. At a suitable temperature, after about 16-25 days, juvenile leeches hatch from the cocoon and begin an independent life.
Precautions for leech culture
1. Pay attention to preventing escape: Build an escape-proof wall around the pond, with a height of more than 80-90 cm. The inner side of the wall should be plastered with cement and sand into a rough surface.
2. Stock a large number of aquatic plants: Mainly water hyacinth and duckweed. Leeches are afraid of direct sunlight, so planting a large number of aquatic plants can both serve as feed for river snails and provide shade, and leeches can also lay eggs on them.
3. Provide sufficient feed: About 50 kg of river snails should be put into every 667 sq m of water surface. In addition, livestock and poultry blood clots should be provided to the leeches once a week, but the blood clots must not contain salt. To avoid affecting water quality, the blood clots must not be put directly into the water. The blood clots can be placed on wooden blocks so that they float on the water surface. After the leeches smell the scent, they can climb up to feed. The blood clots must not be left in place for more than two days.
4. After introduction, the leeches must not be put directly into the pond: because during transportation the leeches themselves produce a layer of mucous membrane as a protective film. A cool, damp place should be chosen around the pond, and the leeches should be placed inside it to let them crawl into the pond on their own, so as to reduce death.
5. Pay attention to observation: Leeches reproduce in the soil under the cover, not in the water. During the reproduction period, if water covers the soil bed for about 7 days, the leech eggs will die from lack of oxygen, so attention should be paid to checking to ensure successful culture.
6. Timely capture: The capture period is generally in October. The harvested leeches are separated into large, medium and small. The large ones are selected out and put back into the pond to be kept as leech breeders; the small ones are placed in another pond to continue being raised, so that in the second year, when they reach more than 15 g, they can be harvested and sold; the medium ones should immediately be processed into dried products and sold.
Leeches have extremely strong survival ability, reproduce quickly, and have high medicinal value. Now the culture technology is becoming more and more mature, and they are a kind of aquatic animal very suitable for everyone to choose to raise.