How to Raise Leeches in Northern China? Breeding Methods and Key Technical Points
When it comes to leeches, perhaps everyone's impression of them is not particularly good, because they are blood-sucking creatures, but leeches still have many uses, and they have very good medicinal effects in some respects, so quite a few people are now breeding leeches.
Leech Ecological Habits
1. Living habits: Leeches are cold-blooded mollusks and can grow and reproduce in both northern and southern China. They mainly live in freshwater reservoirs, ditches, paddy fields and lakes and marshes, and are most abundant in ponds rich in organic matter or in unpolluted small rivers. The suitable growth temperature is 10-40°C. In northern regions, when the temperature is below 3°C, they enter a dormant overwintering period in the mud, and in March-April of the following year, when the temperature rises above about 8°C, they emerge from dormancy and become active. Leeches are omnivorous animals, and their main way of life is sucking the blood or body fluids of animals. They often feed mainly on aquatic plankton, insects and mollusks. Under artificial conditions, they are fed various animal internal organs, cooked egg yolk, compound feed, plant residues, freshwater snails and shellfish, miscellaneous fish, earthworms and so on.
2. Reproductive habits: Leeches are hermaphroditic, mating with different individuals and fertilizing internally. They possess both female and male reproductive organs at the same time. During mating, they position themselves in opposite directions. In their life history there is a phenomenon of "sex reversal", with an exchange of gender roles. A single leech can be both a father and a mother, playing different roles at different stages of its life. About one month after mating, the female reproductive organs secrete a thin mucus, which encloses an egg band in the middle, shaped like a "silkworm cocoon", and is discharged from the body. It hatches in moist mud. With a suitable temperature, after about 16-25 days, young leeches hatch from the cocoon and begin an independent life.
Construction of Breeding Ponds
Leeches have extremely strong adaptability, tolerate a wide range of temperatures, and can withstand hunger and drought, and can live in all kinds of waters. General lake grounds, fish ponds, low-lying waterlogged land, paddy fields, river ditches, and idle land in front of and behind houses can all be used to build ponds for breeding according to local conditions. For large-scale breeding, a site sheltered from the wind and facing the sun, convenient for drainage and irrigation, and where escape is prevented should be chosen for pond construction. Various fish ponds or low-lying waterlogged land can also be chosen for transformation and use. For convenience of management, the pond area should not be too large. The water depth is generally about 1 m. One inlet and one outlet are set at opposite corners of the pond. Some stones, tiles or branches are placed at the bottom of the pond for them to inhabit. In production, we use abandoned river ditches, dig partitions, and build series-connected ponds of varying sizes, with every 2-3 ponds as a group. The shared ridge between two ponds is dug through, leaving a passage for water intake and drainage, which can both enliven the water body to facilitate exchange and make management and harvesting easier, achieving very good practical results.
Sources of Seed Stock
1. Capture natural breeder leeches for self-propagation. From July to October, when leeches are active and frequently appear, capture adult leeches from natural waters as breeder leeches, place them in a certain body of water to preserve the stock through winter, and the leeches can reproduce on their own the following year. Adult leeches with a body length of more than 6 cm, under suitable conditions, can reproduce about three times a year. Self-propagation and self-rearing is a convenient and labor-saving approach and development direction. During reproduction, a considerable number of river snails can be put in at one time, generally 25-30 kg per mu, and the water quality should be regulated and controlled well. During the hatching period, feed once every 5-7 days. At the beginning, the bait is cooked egg yolk rubbed into pieces and splashed on. In the middle and later stages, animal blood mixed with bran, peanut shell powder or chicken and pig feed is used for feeding. The technique is simple and easy to carry out.
2. Purchasing seed stock. Go to an artificial breeding farm and select young leeches of uniform size, lively and strong, and able to stretch and contract properly as seed stock.
3. Stocking the seedlings. According to different breeding conditions, different stocking densities can be chosen. In well-equipped small cement ponds for intensive rearing, up to 1000-1500 leeches per sq m can be stocked. According to experience, for pond breeding of about 0.3-2 mu, 100-300 breeder leeches can be fully stocked at one time per pond and they can reproduce on their own. Young leeches generally reach gonadal maturity in 120-150 days. In northern regions, seedlings stocked in the same year can reproduce a second generation in that same year. Breeder leeches reproduce 2-3 times a year, with each individual laying about 300 eggs.
Feeding and Management
1. Feeding. Natural bait types are mainly freshwater snails, earthworms and some insects. Large-scale breeding is supplemented by feeding various animal blood, internal organs and freshwater fish, shrimp, shellfish and snails, as well as livestock compound feed and crop straw. In pond breeding, a certain number of wild river snails or golden apple snails can be put in, generally about 0.05-0.1 kg per sq m, to let them reproduce naturally and grow together with the leeches for them to prey on. The number of snails put in should not be too large; if too many, they compete with the main breeding species for living space, and host and guest may switch roles. When feeding animal blood or mixed bait, attention should be paid to feeding at intervals and promptly removing leftover bait. This is even more important in hot weather, so as to avoid pollution and deterioration of water quality, which would affect leech growth.
2. Daily management. Leeches have very few diseases. The main task is regulating water quality. Although leeches are not strict about the environment and water quality, excessive changes in or deterioration of the water environment will affect their growth and reproduction. During breeding, the water temperature is generally kept between 10-40°C. For breeding water that is too fertile or too polluted, a certain amount of dissolved oxygen must be maintained. Generally, the dissolved oxygen in the water body should be greater than 0.7 mg/L. If oxygen deficiency occurs, small water bodies can be dealt with by artificial sprinkling of water, while larger water bodies should promptly be injected with new water or have their water changed. In the high-temperature summer season, maintaining relatively fresh water quality is very important.
Overwintering in Greenhouses
Affected by region, leech breeding in northern China should establish solar overwintering greenhouses under artificial conditions, in order to break their hibernation habit, increase breeding time and shorten the time to market. Solar greenhouses are generally of a bamboo-wood and plastic covering structure. The northern wall is made of rammed earth or brick-concrete, 0.8-1.5 m thick, oriented east-west, 30-50 m long, with a north-south span of 10-15 m, and 5-7 rows of main pillars. The top is covered with anti-drip plastic film and rollable straw mats, with doors, passages and vents left. In severe cold and snow-bound seasons, snow removal and artificial heating measures should also be taken. More advanced greenhouses can use a steel-plastic column-free method, but the cost is relatively higher.
By building solar greenhouses, catching the large and keeping the small in a planned way, and concentrating them for overwintering, daily management during this period should closely monitor temperature changes inside and outside the greenhouse, as well as oxygen supplementation, wind prevention and cold resistance, so as to ensure the normal growth and overwintering of leeches and prepare enough leech seed for the following year.
Harvesting and Processing
1. Harvesting methods: The methods for harvesting and catching leeches generally include the following: (1) fixed net catching; (2) seine net catching; (3) draining water catching; (4) mechanical catching.
2. Processing methods: (1) Lime burial method: mix lime evenly with the leech bodies, bury for about 20 minutes, sun-dry or oven-dry, and sift out residual powder. (2) Hot water scalding method: pour freshly boiled water into a container holding the leeches, cover and seal for 30 minutes, then remove, wash and air-dry. (3) Alkali burning method: stir edible alkali powder with the leeches, or turn and rub them by hand, causing them to contract to death, then rinse with water and sun-dry. (4) Raw sun-drying method: thread a thin wire horizontally through the leeches and sun-dry them directly in the sun until dry.
As a famous, special and high-quality breeding variety, leeches have the characteristics of fast growth, high yield, easy promotion, small investment and quick results, and one introduction of seed stock benefits for many years. They are suitable for breeding in all sizes and ways in both urban and rural areas. At a time when natural leeches are extremely scarce and market demand is soaring, developing artificial breeding is imperative, with obvious benefits. It is a fast path to wealth for the broad masses of urban and rural people, and has great breeding prospects and development space.