│Xu Meng│
Associate Researcher of pearl river fisheries research institute of Chinese Academy of Fishery Sciences, his research direction is invasion ecology, and his main research content is the invasion mechanism and ecological impact assessment of alien aquatic organisms. He has presided over the National Natural Science Foundation of China, the Natural Science Foundation of Guangdong Province, and the special project of "Pearl River Science and Technology Rising Star" in Guangzhou. He won the second prize of Guangdong Science and Technology Progress Award, the second prize of Fan Li Science and Technology Award, and the third prize of Science and Technology Progress Award of China Academy of Fishery Sciences.
│Fang Miao│
Ph.D., his research interests are invasion ecology, the main research content is the invasion mechanism of alien aquatic organisms and ecological impact assessment.
In the list of invasive aquatic organisms, Fushou snail is "on the list". They are highly reproducible and can spawn in large quantities in waters, and in water environments such as rivers, farmlands, ditches and ponds, they can often find some oval or spherical pink objects adhering to pipes, stones, aquatic plants, fields or wooden stakes that leave the water, each of which contains tens to hundreds, or even thousands of Fushou snail eggs.
When did Fushou snails invade Guangdong, what kind of harm they would bring, and how should they be prevented and controlled? With questions, the reporter found Dr. Xu Meng and Dr. Fang Miao of the Pearl River Fisheries Research Institute of the Chinese Academy of Fishery Sciences to answer. Xu Meng pointed out that since the invasion of China in the 1980s, Fushou snail is one of the first 16 alien species to invade China, bringing serious ecological and economic harm. After years of research and exploration, physical, chemical and biological prevention and control measures for Fushou snail have been formed.
The Four "Counts"
Q "Oceans and Fisheries": Where does the snail come from and what hazards will it cause?
A
Xu Meng: Fushou snail, also known as apple snail and large bottle snail, is an amphibian freshwater shellfish mollusk of the order Mid-gastropods, gastropods, bottle snails and the genus Bottle snail, native to the Amazon River Basin in South America, and has caused different degrees of damage and threats to biodiversity, agricultural production and human health on a global scale. In 2000, the International Union for Conservation of Nature (IUCN) Expert Committee on Invasive Alien Species listed it as one of the 100 malignant invasive alien species in the world.
▲ Fushou snail eggs
▲ Fushou snail
In 1981, the Fushou snail was introduced to Zhongshan City, Guangdong Province as an economic food animal, but was abandoned and rapidly spread due to poor food taste and market failure. Due to its adaptability, rapid growth, high fertility and lack of natural enemies, natural populations have been established in many southern provinces of China, and huge economic losses have been caused. In 2003, the former State Environmental Protection Administration also included it in the List of The First Invasive Alien Species in China, one of the first 16 invasive alien species in China.
The harm of Fushou snail is mainly reflected in four aspects. The first is to cause serious economic harm to crops such as rice. Fushou snails can eat rice seedlings in large quantities, and about millions of hectares of rice in major provinces in southern China suffer from different degrees of harm from Fushou snails every year. According to reports, in 2006, more than 4.5 million mu of rice was affected by Fushou snails in the country, and 2.5 million mu of crops were affected in Guangxi alone. In the hardest-hit areas of Fushou snail in Fujian and other provinces, rice yields decreased by 30% to 50%. The annual cost of pesticides used to control rice Fushou snails nationwide is estimated to be close to or more than 2 billion yuan. In addition to rice, Fushou snail is also harmful to crops and vegetables such as Zibai, Lingjiao, Cigu, Ziyunying, Hollow Cabbage, and Mustard Fruit. The second is to destroy aquatic biodiversity. Fushou snail competes with native snails for resources, resulting in the reduction or disappearance of native species; Fushou snails are heterogeneous and can feed on large aquatic plants, plankton algae, attached plankton, inorganic and organic detritus, etc., interfering with or changing the composition and structure of aquatic communities and affecting ecosystem functions. Third, the excrement of Fushou snail affects the water environment. The amount of food and excretion of Fushou snail is very large, and its large amount of excretion will lead to an increase in the content of ammonia nitrogen, nitrate nitrogen and dissolved phosphate in the water, a decrease in the dissolved oxygen content and redox potential, change the physical and chemical properties of the water body and the microbial content of the water body, and affect the ecosystem function. There is evidence that the snail inhibits the growth of native species by changing the nature of the water body, and that the high tolerance and resistance of the snail makes it less affected. The fourth is the impact on citizens' health. Fushou snail is the intermediate host of Guangzhou tube strong nematode that causes human acidophilus meningitis, and there have been cases of eosinophilic meningitis caused by eating Fushou snail in Zhejiang, Beijing, Fujian, Guangdong and Taiwan in China.
Fushou snail has a strong ability to survive
Q "Oceans and Fisheries": Why did Fushou snails explode and what are the driving factors?
Xu Meng: First, the reproductive ability of Fushou snail is amazing. Its lifespan is affected by water temperature and food abundance, generally 2 to 5 years. Sexually mature Fushou snail mating, the male snail crawls on the female snail shell, the male snail penis sheath is turned out and inserted into the female hole of the female snail, the mating time is as long as 2 to 4h, after mating is completed, fertilization is carried out in the body, this precise mating strategy, resulting in it has a strong reproductive ability. In addition, in the natural population of Fushou snail, the number of individuals of female snails is often more than that of male snails, and each male snail can mate with different females many times, ensuring the continuous growth of its population. Fushou snail can generally produce 2 to 3 generations in 1 year, and the young snail can reach sexual maturity in 3-4 months, with the phenomenon of "three generations in the same house".
Second, the food sources of Fushou snail are diverse, and the ability to endure hunger is strong. When food is more abundant, Fushou snail will give priority to foods with higher nutrient content, preferring the more tender parts of the plant. Fushou snails can not only feed on phytoplankton and large plants, but also use aquatic insects, crustaceans, small fish, etc. as food, which provides sufficient food guarantee for its rapid growth. Fushou snail has a unique digestive system, and the digestive enzymes in the body work efficiently and synergistically, making it have a more adequate digestion and absorption capacity for food. Even in extreme hunger, the snail can cope by slaughtering its own species, feeding on snail eggs, or eating the carrion of some aquatic animals. In addition, the hunger tolerance of Fushou snail is also very strong, even in the absence of food, 39% of individuals can survive for 6 weeks, and a small number can even survive for 20 weeks.
Third, Fushou snail has a strong ability to resist unfavorable environments. Fushou snail in China has two or more times to be introduced in the situation, the gene variation is larger, the apparent plasticity of the snail body is stronger, so it has a strong potential adaptability to environmental changes, which to a certain extent enhances the invasion of Fushou snail, coupled with the suitable climate in South China, rich and diverse water environment, which provides a unique climate and resource guarantee for the successful invasion of Fushou snail. Fushou snail has the ability to cope with low temperature environment, such as in the winter when the temperature is low, it can reduce metabolism, respond to unfavorable low temperature environment by hibernating, and can also enhance its cold tolerance through the accumulation of certain specific substances (glycerol, sugar, etc.) in the body. Therefore, there is a risk of further spread of Fushou snails to cold areas in China. In the summer when the temperature is too high, the snail can hide under the lush aquatic grass or crawl to the deep water through the developed motor organs, or cope with the long-term high temperature weather by sleeping in summer. During the dry season, snails of different sizes and physiological states can survive for 3-29 months in anhydrous or arid conditions, and even newly hatched young snails can maintain a survival rate of more than 50% after 8 days under the threat of drought. In addition, Fushou snail can either cope with drought by regulating its own metabolic level to reduce energy consumption, or it can maintain normal vital signs by losing a certain amount of water in the snail body and increasing its osmotic pressure to prevent further loss of water in the body.
Fang Miao: The growth of Fushou snail has no harsh requirements for water quality. In clean and oxygen-soluble water, the snail can breathe through the gills, and in water with a lower oxygen content, the snail can extend the lung straw out of the water for gas exchange. It has been reported that Fushou snail can still survive for a period of time in almost oxygen-free water, and the short-term deterioration of water quality will not have a significant lethal effect on it, and it is also very adaptable to the pH in the water. At the same time, Fushou snails are more sensitive to threats from predators. When encountering predators, the snails will quickly bury themselves in the dirt to hide, while the young snails often choose to escape quickly, this strategy greatly reduces their own casualties, coupled with the red alert color of the egg and the chemical neurotoxins contained in it also greatly reduce the threat of predators. In short, the unique reproductive characteristics, extensive ecological adaptability and tolerance of Fushou snail provide strong ecological advantages for the diffusion and outbreak of its population.
Compound methods of prevention and control
Q "Oceans and Fisheries": What are the prevention and control measures for Fushou snails, and what are the suggestions?
Xu Meng: At present, the control methods of Fushou snail in China mainly include chemical control, agricultural control, physical control and biological control. Among these means of prevention and control, chemical control is the most commonly used method, and the effect is the most obvious, but it will cause water pollution and the cost of use is also high. Commonly used drugs include tetraacetaldehyde, spirantine, sodium pentachlorophenol, berriosis, thrombosis, mida, 100 snail enemies, copper sulfate, these drugs can kill Fushou snail relatively quickly, but have disadvantages or serious side effects. For example, the toxicity and residue of sodium pentachlorophenol are very strong, long-term intake of water contaminated by it will cause carcinogenic teratogenicity; berrhoe killing is also a deadly poisonous substance for non-target fish, frogs and other aquatic organisms, and it is very easy to pollute water bodies when it is not strictly controlled; Bailuo killing and Mida are imported drugs with high costs; Bailuo enemy drugs are slow and need to be applied before seedlings; copper sulfate is a heavy metal salt, which has a polluting effect on water bodies.
Fangmiao: Commonly used agricultural control methods include the use of water and drought rotation, such as changing rice fields to vegetable fields, and Fushou snails will die of suffocation due to lack of water. Every winter, by sorting out ditches and cleaning up silt, the Fushou snails that are ready to overwinter are exposed to the air, and the density of Fushou snails can be effectively reduced by sunlight exposure, low temperature invasion and water shortage suffocation. Physical control methods mainly include manual picking, trapping, hunting and killing Fushou snails, and collecting Fushou snail egg blocks. The advantage is that there is no pollution, but the efficiency is not high, and the labor cost is higher.
In terms of biological prevention and control, ecological models such as duck culture in rice fields and fish culture in rice fields can be adopted, and the characteristics of bluefish, carp, Chinese turtles and ducks feeding on Fushou snails may have good application prospects. The transformation of Fushou snail is also one of the better means of biological prevention and control, such as trying to use snail meat as feed on a large scale, or using snail eggs to extract astaxanthin as a coloring feed additive for ornamental fish, etc., but the conversion efficiency may not be high, the cost is not low, and large-scale production has not yet been formed at this stage. The screening and extraction of plant snails is also one of the effective means. Experimental studies have shown that extracts such as five-clawed golden dragon and blood water grass have a good killing effect on Fushou snail, but the production process related to plant extract has not been formed, and the cost may also be high, and it is temporarily impossible to promote and use it on a large scale. The direct use of tea meal instead of chemical drugs to prevent and control Fushou snail is also one of the commonly used biological prevention and control methods in Jiangxi and other places.
Xu Meng: In view of the current prevention and control methods and effects, it is recommended to adopt a combination of multiple prevention and control methods, and focus on the development of Fushou snail ecological regulation technology. Make full use of the predatory effect of fish and ducks on Fushou snails, and explore a scientific and effective ecological regulation technology for rice field (water body) - fish (duck) - Fushou snail that can control the spread of Fushou snail and reduce harm.
In the next step, relevant scientific research units and enterprises should speed up the pace and develop more practical Fushou snail prevention and utilization technologies. First, the research on emergency control technology of Fushou snail. Select efficient prevention and control drugs, and try to develop new chemical snail control technologies that are efficient, economical, environmentally friendly and suitable. The second is the screening of Fushou snail plant snail. Extensive screening of plant extract compounds with snail killing effect in nature, selection of effective plant snail killers, and attempts to carry out related production processes. The third is to carry out research on the utilization of Fushou snail meat, snail egg coloring, multifunctional cellulase EGXA, antibacterial peptides, etc., and try to develop and utilize Fushou snail resources to "promote control with use".
Finally, it is recommended that the government strengthen the supervision of the introduction and breeding of various alien species to prevent escape and spread; improve the system for alien species or ornamental alien species caught in the wild to strictly prohibit arbitrary release or discarding; expand publicity efforts to improve the public's awareness of the prevention and control of the harm of foreign species.
│Further reading│
How to distinguish between Fushou snail and common edible snail
Fushou snail is hermaphroditic, larger, with a complete spiral-shaped shell. The shells are yellowish brown and have a smooth surface. The snail is rotated to the right, the shell is approximately disc-shaped, there are 5 to 6 spiral layers, and the body snail layer is expanded. The female shell mouth is thin, the outer lip is straight or slightly curved, and the perimeter edge of the three is flattened; the male shell mouth is thickened, the outer lip is tilted outwards, the middle of the outer edge of the three is slightly raised, and the upper and lower edges are concave towards the soft body.
Chinese round field snails are distributed in all freshwater waters in China, medium-sized individuals. The shell is thin and strong, with a wide conical shape, with 6 to 7 spiral layers, all convex, each spiral layer is high and the width grows rapidly. The shell top is sharp. The shell surface is yellowish brown, smooth, ribbed, with a fine and pronounced growth line. The shell mouth is oval, the periphery is intact, with black rim edges, and the umbilical hole is suture-shaped. The mantle is ovate, yellowish brown, with pronounced concentric growth lines, the nucleus is near the center of the inner lip.
The Chinese round field snail is mainly distributed in the northern provinces and regions, and the shell is slightly smaller than that of the Chinese round field snail. It is hard and ovoid in shape. There are 6 to 7 spiral layers, each of which grows rapidly in width; the spiral part is wider and shorter than the previous type, and the body spiral layer is extremely expanded. The shell top is sharp. The shell surface is yellowish brown or yellowish-green, smooth, ribbed, with a pronounced growth line. The shell mouth is oval, the periphery is intact, with black rim edges, and the umbilical hole is suture-shaped. The three are the same as the Chinese round field snails.
Source: Marine & Fisheries
Reporter: Li Yishan