Fund project: Zhejiang Qingyuan alpine thin shell field snail rice field planting technology

Fund project: Zhejiang Qingyuan alpine thin shell field snail rice field planting technology

Fund Project: Zhejiang Agricultural Technology Extension Foundation Funded Project (LNTJZ2018); Zhejiang Province "100 Million" Third Level "Excellent Skilled Talents" Training Project

（QRS2018-190）。

_ Wu Weijun

Field snail, generally refers to the mollusk of the field snail family. The daily so-called field snail belongs to the mollusk phylum, gastropods, middle gastropods, field snail family, and round field snail genus. Alpine thin shell field snail, commonly known as: Hehu field snail, thin shell field snail, is a unique, rare variety, identified as a new variety: Hehu round field snail, basically only exists in the alpine area of Lishui City, Zhejiang Province, mainly distributed in Qingyuan County, Zhejiang Province, Baishanzu Town, Hehu, Sandui, Lanni, and Hedi Town and other areas at an altitude of about 1000 meters, with a long history of breeding. Compared with ordinary field snails, it is known for its thin shell and translucent shape, which can be crushed by hand, and can be broken by biting with teeth when eating. The meat is delicious and nutritious, known as the reputation of "alpine abalone", with high popularity, quite popular, high market price, short supply, broad prospects, is a characteristic industry that increases income and enriches the people. After practical exploration, a set of alpine thin-shell field snail rice field planting and breeding technology has been summarized and formed, with double production and double harvest, aiming to provide reference for promoting industrial development and technology promotion.

1 Biological characteristics of field snails

The snail is hardy and afraid of heat, is active at night, and inhabits the environment of warm winter and cool summer, fresh water quality, abundant bait, and soft soil, and often gathers in cool micro-flowing water, such as water inlets, flowing ditches and other places. The optimal temperature of the field snail is 20 to 28 °C, when the temperature is lower than 10 °C or higher than 30 °C, the field snail will burrow into the mud, grass, etc.; when the temperature rises to about 10 °C, it will climb out of the activity; more than 40 °C, the field snail will die.

Hermaphroditic, the female snail is large and round, and the male snail is small and long. The left and right antennae of the female snail are the same size, the head is extended out, and the right antennae of the male snail are shorter and thicker than the left antennae, and the end is spiral-shaped and curved inward to the right, specializing as a handover. Lifespan is generally 4 to 5 years for females and 2 to 3 years for males. The snail is an oviparous animal, and fertilization, embryonic development and snail development are all completed in the mother's body. Generally, sexual maturity is 1 year old, and the breeding period is from March to October, and the spring and autumn season is the peak period of breeding. The number of litters is produced in batches, the number varies with the environment, pro-snail, etc., each fetus produces 3 to 20, as many as 20 to 50, and can produce 50 to 200 a year.

2 Prepare before stocking

2.1 Rice field selection

Rice fields require sufficient water sources, excellent water quality, fertile soil, good water retention, convenient drainage and irrigation, no drought and flooding, leeward to the sun, and suitable altitude.

2.2 Reinforcement of the field

The mound is heightened and widened to 40 cm to ensure that it does not collapse, does not leak, can store water, and facilitates daily work. According to the actual situation, the aquaculture geomembrane can be laid on the inner slope of the field for reinforcement.

2.3 Takubo Yoda Mine

Depending on the size of the field block, a circular ditch can be excavated on the inner side of the field, which is 20 to 30 cm wide and 10 to 30 cm deep, and can maintain a water depth of more than 10 cm at high temperatures; the field ditch of "ten", "feng" and "well" can be excavated in the field, which is 20 to 30 cm wide and 10 to 30 cm deep, and is connected to the ditch. In addition, the field pit can be excavated, 10 to 30 cm deep, the shape can be rectangular, square, etc., the position can be in the field or around, the four corners, and the ditch, the ditch is connected. When excavating facilities such as trench pits, care should be taken to avoid damaging the tillage layer, and the area of the ditches and pits generally does not exceed 7% of the area of the paddy field.

2.4 Inlet and drainage facilities

To create a micro-flowing water environment, generally set up water inlets and drainage outlets on the diagonal fields of rice fields. In order to prevent the escape of snails and the entry of predators, debris, etc., facilities such as fences must be set up at the inlet and outlet outlets.

2.5 Disinfection and fertilization

Before stocking snails, use quicklime and other clear fields for disinfection, the water level of the paddy field is about 15 cm, and the amount of quicklime is 450~750 kg/hm 2. Rice field fertilization is mainly organic fertilizer, supplemented by chemical fertilizer, more base fertilizer, less topdressing. Field snails are very sensitive to chemical fertilizers, and chemical fertilizers such as ammonium bicarbonate are prohibited. Preferential use of green manure, farm manure, biological bacterial fertilizer and other fertilizers. Chopped straw and livestock and poultry fertilizer can be mixed and fermented in a ratio of 1:3 as a base fertilizer, and evenly spread with an amount of about 4000 kg/hm 2. Fermentation must be completely thorough and fully stacked, from raw fertilizer to mature fertilizer, otherwise it is easy to produce harmful gases such as methane and hydrogen sulfide, which is not conducive to snail farming. You can also use methods such as burying straw, but pay attention not to too much, so as not to affect the breathing of the bottom snail. If chemical fertilizer is really needed, it is advisable to use methods such as "point application" at the base of rice. Topdressing should be a small amount of multiple times, pay attention to protect the safety of the field snail, first discharge part of the water, introduce the field snail into the ditch, and then apply topdressing. Before stocking, test the toxicity and medicinal properties of the water with a small amount of snails to avoid serious losses. In addition, the first rice field to be cultivated must be ploughed and loosened. In the later stage and the second planting, according to the actual situation, the soil can be ploughed or the rice roots can be shoveled to keep the bottom mud soft.

3 Field snail stocking

3.1 Snail seed selection

Snail seeds should be collected in local rice fields, or they can be locally farmed or purchased locally. It is necessary to pay attention to the quality of the seedlings, and healthy and high-quality snail seedlings with round body, frightened rapid return to the shell, tightly closed and strong lid, intact shell, clean shell surface, and no parasites in the snail body should be selected.

3.2 Stocking time

Stocked in batches from March to June and September to October, it can also be stocked at one time, and is generally released in April in alpine areas. The hot heat should be avoided to improve the survival rate, and the seedlings should generally be stocked after they have returned to green. If it is the first time to breed, it is advisable to stock the snails before breeding. When dispensing, it should be gently handled, evenly distributed, and carefully identified to avoid mixing other snails.

3.3 Stocking density

According to the actual situation, the regulation of 1.25 to 2.5 g / field snail 120 000 ~ 300 000 /hm 2; the specification of 5 g / only left and right field snail 150 000 /hm 2; specification 10 g / only about the field snail 30 000 ~ 50 000 /hm 2 , And appropriate amount of breeding of bronchs, but pay attention to the individual should not be too large, so as not to be too old, limited life. The male-to-female ratio is 3:1.

4 breeding management

4.1 Feeding of bait

Field snails are omnivorous animals, mostly feeding on tanaka humus, microorganisms, algae, etc., and can be artificially fed rice bran, wheat bran, grass, potato vine, corn leaves, pumpkin vine, compound feed, etc. Feeding time and place must be fixed, generally selected in the morning or evening, every 1 to 2 days feeding 1 time, feeding amount, frequency can be adjusted according to the feeding, environment and other conditions, to avoid one-time feeding too much, too frequent, to prevent water quality deterioration. When the water temperature is below 15 °C or above 30 °C, the snail does not feed or the amount of food intake is reduced, and it can be fed less or not in case of rain. The number of feeding points is appropriate, evenly distributed, forming a feeding field, which is conducive to feeding and reducing waste.

4.2 Water quality level

Aquaculture water requires rich bait, fresh water quality, dissolved oxygen of more than 3.5 mg/L, and it is advisable to maintain micro-flowing water. According to the growth of rice snails, timely and reasonable adjustment of the water level, usually the water depth of about 10 cm, rice rooted tillers, jointing and pregnant ears and other periods, to maintain the water level of the field ditch pit. In case of high temperature weather, the water level should be raised. When the water quality deteriorates and there is a lack of oxygen, new water should be added in time. In the hot summer, the water temperature is high, and it is advisable to change the water appropriately; the water temperature in the early spring and autumn is low, and the water can be changed less.

4.3 Escape prevention and disease prevention

Field snails are easy to escape from inlet and drainage outlets, water-filled fields, etc., and must patrol the inlets and drainage outlets every day to prevent blockage and damage. On particularly rainy days, it is necessary to dredge the drainage inlet in time to prevent the water from escaping from the field, and at the same time prevent the collapse of the field caused by the full water.

In aquaculture, if the field snail tablets are sunken, it indicates that the bait is insufficient, and the amount of feeding should be increased; the three pieces shrink and the snail meat overflows, indicating calcium deficiency, and calcium-containing bait can be added appropriately or sprinkled with quicklime in an appropriate amount, but be careful not to overdose.

The enemies of the snail are birds, rats, snakes, ducks, ants, water centipedes and so on. To prevent ducks and other waterfowl from entering the rice fields to eat, ants can be trapped with loofahs and grass handles soaked in pig's blood. The grass and other grass in the field should be cut in time to prevent rats, snakes and other predators. Where conditions permit, a fence can be set up on the inside of the field to prevent enemies and to prevent the snail from escaping. In addition, snail rice paddies should not stock carp, catfish, bluefish, tilapia and other fish to prevent eating field snails.

For the prevention and control of rice diseases and insect pests, ecological control methods should be adopted, and insect pests can be used to kill insecticidal lamps and biological control. Use pesticides with caution, when it is really necessary to use, it is advisable to choose high-efficiency, low-toxicity, compliant pesticides, spray on sunny days, increase the water level in advance, and make the nozzle diagonally upward, apply in rice stems and leaves, etc., to avoid a large number of pesticides falling into the rice field water.

4.4 Wintering management

Before entering the winter, strengthen the cultivation to make the field snail physically strong. After entering the winter, the water temperature drops to 7 ~ 9 ° C, the field snail drills into the mud to hibernate, does not eat, only leaves small holes in the mud surface to change the water to breathe, to ensure that the water depth is more than 15 cm, in order to facilitate heat preservation, you can also put an appropriate amount of straw in the field, etc., for its overwintering.

5 Capture and transport

5.1 Field snail harvesting

When the size of the snail reaches about 10 g/ only, it can be harvested in batches, but it should avoid the peak of breeding and be staggered. According to the life habits of field snails, they are harvested at noon in spring and winter, and in early morning or evening in summer and autumn. In accordance with the principle of catching large and leaving small, small snails and broodstock snails are retained for subsequent breeding and use. In addition, when harvesting rice, try to use manual harvesting or small harvesters to avoid damage to the field snails, and pay attention to the rice field water is not drained, keeping the field ditch moist.

5.2 Field snail transportation

Field snail transportation is more convenient, can be used in ordinary baskets, barrels, bags, boxes, etc., but pay attention to keep moist, prevent exposure, avoid squeezing. During high temperatures such as summer, it can be transported in foam boxes with a little ice pack.

6 Benefit analysis

The snail grows out of 40-100 pieces/kg, with an average size of 75 pieces/kg, and the snail yield is 375-750 kg/hm 2 and the average yield is 585 kg/hm 2. Rice yield was 3900~7500 kg/hm2, with an average yield of 6000 kg/hm 2. After deducting the cost of field contracting (circulation), facilities and equipment, labor, seedling seeds, feed, etc., compared with conventional rice planting, it can increase the income by 4950 yuan / hm 2, and the benefit is greatly improved (Table 1).

Table 1 Yield and benefit of breeding

7 Discussion and conclusions

Alpine thin-shelled field snail rice field cultivation, generally suitable for multi-terraced mountain hills and other places, with the help of natural terrain drop, the use of micro-flowing water method to carry out field snail culture. Due to the conventional cultivation of rice, tillage, fertilization, medication, drying, harvesting and other operations, will affect the growth of field snails, and protective measures must be taken. The stocking density of field snails is not recommended to be too large. Fan Huihui's research showed that the quality increase rate, specific growth rate, the number of litters of a single female snail, and the average weight of the snail decreased with the increase of the breeding density, and the final weight and survival rate of the snail also decreased with the increase of the breeding density. The above studies show that high-density breeding may directly affect the growth of bronchs, and affect the development of gonads, fertilized eggs, etc., thereby indirectly affecting the number of litters, resulting in adverse effects on the growth, reproduction and survival of field snails. Therefore, in order to pursue high yield and high efficiency, blindly increase the density of breeding, it is advisable to choose reasonably according to the actual situation.