What Are the Methods for Farming Leeches? A Detailed Explanation of Common Farming Models
The leech, commonly known as the bloodsucker, was already recorded in the Shennong Bencao Jing and has high medicinal value [1]; it grows and reproduces in inland freshwater waters and is a traditional specialty medicinal aquatic animal of China. Its dried products, after being steeped and prepared, are used in traditional Chinese medicine and have effects such as treating stroke, high blood pressure, clearing blood stasis, amenorrhea, and traumatic injuries. In recent years it has been newly discovered that leech preparations have special efficacy in the prevention and treatment of cardiovascular and cerebrovascular diseases and in anti-cancer applications. Historically it was mainly obtained by natural harvesting, but due to the abuse of pesticides and chemical fertilizers in recent years, as well as pollution of the environment by the “three wastes” of industry and agriculture, wild natural resources have sharply declined. With the in-depth development of the leech's medicinal value, its market demand potential is enormous. In southern China around 1995, people began to harvest natural seedlings and conducted artificial rearing for the first time, achieving success.
There are many ways to farm leeches. The following are several common farming methods introduced to you.
1. Extensive outdoor farming
Extensive outdoor farming is a farming method that uses natural conditions and provides protection after enclosing a farming area. Extensive outdoor farming does not mean leaving everything unattended; it is also necessary to release sufficient seed stock, appropriately add bait, and finally harvest. It generally includes reservoir farming, pond farming, marshland farming, lake farming, river channel farming, lowland farming, and rice paddy farming, etc. These methods have relatively large farming areas, ample light, abundant natural bait, small investment, and large returns. However, the yield per unit area is relatively low, and it is not easy to manage; attention must often be paid to preventing natural enemies, preventing escape, and dealing with changes in water level rise and fall. Two of these farming methods are briefly introduced below.
Marshland farming
Marshland is characterized by shallow water levels, luxuriant aquatic plants, relatively high contents of organic matter and humus in the bottom layer, and abundant plankton and aquatic animals. Therefore, as long as a fence is built well, leeches can be stocked. Regular observation should be carried out, and bait should be appropriately supplemented. When the density is too high, timely harvesting should be done.
Rice paddy farming Rice paddies are characterized by shallow water levels, suitable water temperature, and shade provided by rice, making them suitable for leech growth and reproduction from oxygen content to abundant bait. Therefore, in most rice paddies in China, different varieties of leeches grow. For rice paddy farming, choose plots with convenient irrigation and drainage, sufficient water sources, soil that retains water, and good fertility, and enclose them with fences all around. In the middle of the rice paddy, dig one or several ponds according to the size of the plot. Generally, it is appropriate to dig one 1 sq m pond in the middle of every 100 sq m, and at the same time dig protective connecting ditches about 30 cm deep and 30 cm wide between the ponds and around the rice paddy, so that the ponds and ditches are connected. When sun-drying the field, leaving the field dry, or applying fertilizer or spraying pesticides, the leeches should be lured into the ponds or protective connecting ditches with animal blood so that they are spared from being killed. It is best to change fertilization to deep application of ball fertilizer, and it is best to change pesticide spraying to low-toxicity or non-toxic pesticides.
2. Intensive fine farming Intensive fine farming is a scientific rearing and management method that uses artificially built ponds and fed bait. It generally includes fish pond farming, farm-area farming, indoor farming, courtyard farming, and factory-style constant-temperature farming, etc. These farming methods have relatively high stocking density and relatively high capital input, and require fine rearing techniques. However, output per unit area is greater and economic benefits are relatively good.
Physical properties of intensive farming 1. Strong light transmission, small fluctuation of the water layer: because the water is shallow, sunlight can penetrate to the bottom of the pond, which is conducive to the healthy growth and development of plankton, submerged plants, and benthic plants. At the same time, because the water is shallow, the upper and lower layers of the water are basically uniform, with only small fluctuations occurring under conditions of wind and temperature differences. This provides a good living environment for leeches. 2. The water color is variable, and the water temperature shows seasonal changes: the color of the water often differs according to soil quality, water depth, type of fertilizer, and the growth and reproduction of plankton in the water. This is because when phytoplankton are numerous the water body appears green, when zooplankton are numerous it appears yellow, when humus is abundant it appears brown or soy-sauce colored, when blue-green algae grow in large amounts it appears blue-green, when Anabaena reproduces abundantly it appears yellow-green, when ciliates flourish it appears brown again, and when water fleas appear in large numbers it appears red. In one year, the water temperature is lowest in winter, gradually rises in spring, is highest in summer, and gradually declines in autumn. During one year, the water temperature is relatively high from May to September, which is the period suitable for leech growth and reproduction under natural conditions. For the average temperature within a day, the water temperature is generally higher than the air temperature, and for the average temperature difference, the water temperature is lower than the air temperature. Viewed in this way, the water temperature is relatively more stable than the air temperature. During the day the water temperature is often lower than the air temperature, while at night the water temperature is higher than the air temperature. 3. If the water body deteriorates, a putrid odor is emitted from the water: if a special rotten smell or stench is found in the water body, it indicates that the water body has been polluted, showing that organic matter at the bottom of the pond, such as leftover bait, sunken remains of animals and plants, and feces, has decomposed to produce toxic gases such as ammonia and hydrogen sulfide. At this time, the water should be changed in a timely manner or the pond should be emptied and cleaned to prevent massive leech deaths.
Chemical properties of intensive farming 1. Acidity and alkalinity (pH value). Acidity and alkalinity refer to the pH value of the water in the pond. It is mainly the change in the ratio between free carbon dioxide and carbonate substances in the water. Its range of variation is generally between 6.5 and 9.5. The pH value changes cyclically between day and night: at dawn, the carbon dioxide content is high and the pH value of the water decreases (becomes acidic); during the day, the carbon dioxide content decreases and the pH value of the water rises (becomes alkaline). Practice has proved that neutral water or weakly alkaline water is conducive to the growth and development of leeches. 2. Amount of dissolved gases. Gases include oxygen, carbon dioxide, nitrogen, ammonia, hydrogen sulfide, and methane (marsh gas), etc. Generally, the more important ones are the content of oxygen and carbon dioxide in the water. When the oxygen content in the water is greater than 0.7 mg/L, leeches move normally; when the dissolved oxygen in the water is less than 0.7 mg/L, leeches will crawl out of the water one after another to the bank soil or grass to breathe oxygen from the air. The content of these two gases in the pond is closely related to the day-night changes in water temperature. The time when oxygen content is highest is in the afternoon, because at this time green plants in the water carry out photosynthesis vigorously, consume carbon dioxide, and produce large amounts of oxygen. At dawn, the oxygen content in the water is lowest, because at night the photosynthesis of plants basically stops, while animals do not stop consuming oxygen and exhaling carbon dioxide. 3. Amount of dissolved inorganic salts. Inorganic salts include nitrates, phosphates, carbonates, and silicates, etc. The dissolved amounts of these salts have a direct impact on the quantity of plankton and other animals and plants, and on the growth and reproduction of leeches.
Biological composition of intensive farming In different regions and different seasons, the biological composition in ponds is clearly different. But generally it consists of the following major categories of organisms. 1. Plankton: plankton are generally tiny animals and plants invisible to the naked eye. Their ability to move is limited, and most move passively by relying on the flow of the water body. They are the main part of the pond's biological composition and have an important impact on the growth and development of leeches. Phytoplankton mainly include lower planktonic algae, such as blue-green algae that reproduce in large numbers in summer (Microcystis, Anabaena, etc.), green algae (Cosmarium, Eudorina, Volvox), and diatoms that grow vigorously in spring and autumn, etc. Zooplankton mainly include the most primitive and lowest class of animals in the animal kingdom. Most of them are single-celled organisms, such as Paramecium, Stentor, and Urocentrum, etc. 2. Aquatic plants: aquatic plants mainly include the following types.
1) Floating plants such as water duckweed and rootless duckweed, etc.; they float completely on the water surface or in the water.
2) Floating-leaved plants have leaf surfaces floating on the water surface, while their roots grow in the bottom soil of the pond, such as water caltrop and water shield, etc.
3) Emergent plants have roots planted in the mud, while their stems and leaves stand upright above the water surface, such as reeds and Alternanthera philoxeroides, etc.
3. Benthic animals: benthic animals include mussels and snails among mollusks, shrimps and crabs among crustaceans, non-planktonic cladocerans and copepods, etc., as well as Hydra, chironomid larvae, and mussel glochidia, etc.
4. Other animals mainly include fish, leeches, water snakes, soft-shelled turtles, water rats, etc.
5. Fungi and bacteria In severely polluted ponds, various fungi and bacteria that endanger the life of leeches reproduce in large numbers, causing a relatively large impact on leech growth.