what exactly is crayfish? Is it a bug? The real name of crayfish is "Procambarus clarkii", and its scientific name is Procambarus clarkii, which is a kind of freshwater shrimp. It is related to lobster, taxonomically, they are all Decapoda. Lobster belongs to the family Lobster, Procambarus or Procambarus, while the crayfish we eat belongs to the family Gryllotaxus (so it is directly called Gryllotaxus in some areas of northern China). Crayfish is native to the southeastern United States, so it is also called American crayfish. Native to the Gulf of Mexico, especially in the mouth of the Mississippi River, it is also called Louisiana crayfish. It is the most edible freshwater lobster variety, and its annual output accounts for 71-81% of the total freshwater lobster output. Were there crayfish in China before? In fact, there are four original authentic crayfish in China, namely, the Northeast Black Crayfish, the Nanjing Black Crayfish, the Procambarus schrenckii and the North Korean Black Crayfish. In addition, there are two kinds of "foreign monks", Procambarus clarkii originated in the United States and Procambarus clarkii originated in Oceania, but Procambarus clarkii is superior in technology and has blossomed everywhere in China, becoming the most famous crayfish. Delicious crayfish is actually an invasive species. This kind of shrimp has fierce temperament, fast reproduction and strong adaptability to the environment, which will also pose a threat to the "aborigines". Crayfish were introduced by genetic modification to destroy corpses? There is a rumor on the Internet: "The Japanese biochemical troops stationed in China have to deal with a large number of corpses, and they have turned crayfish into crayfish through a series of genetic modification, and transported them to the Japanese military station to clean the water." This statement is quite absurd. Watson and Crick discovered the double helix structure of DNA in 1953, and the application research of DNA recombination technology began in the 1971 s. It is simply impossible for the Japanese invaders to engage in genetic modification. However, the crayfish we are eating now are indeed from Japan. In 1927, Japan introduced 21 Procambarus clarkii from the United States, in order to breed and cultivate them as feed for bullfrogs. Around 1931, Procambarus clarkii was introduced to China again. The earliest breeding place was near Nanjing, and it was probably also used as feed. After that, Procambarus clarkii thrived everywhere with its good adaptability. So in terms of time, crayfish's entry into China has nothing to do with Japanese invasion of China, and there is no conspiracy theory. (Read more: How did crayfish get into China? ) Japan doesn't eat crayfish? Don't foreigners eat it? Crayfish has been eaten in the United States for hundreds of years, and the sale of crayfish has gradually moved from country fairs to large-scale transactions. At present, the annual global trade volume exceeds 311,111 tons. Crayfish is a very common cooking ingredient in the United States, and it is usually boiled with potato and corn and seasoned with Cajun. 98% of crayfish used for food in the United States are produced in Louisiana, which selected crayfish as the state representative animal in 1983 and held the "Crawfish Festival" every year. Scene from the Louisiana Crawfish Festival. Image source: After crayfish was introduced into Japan, it was not favored by Japanese consumers. After all, it was "the feed of bullfrogs", and Japan was rich in aquatic products. Comparatively speaking, crayfish meat quality and taste were at a disadvantage. Foreigners who eat crayfish can also look at the export data. In 2111, Hubei Province alone exported more than 8,111 tons of crayfish, and the national export volume was at least tens of thousands of tons. At present, the crayfish food exported is mainly cooked food, such as lobster tail, shrimp, fennel shrimp, spicy shrimp and lobster sauce, which are mainly sold to Danish, Sweden, Spain, Britain, France, the United States, Canada, Japan and South Korea and Southeast Asian markets. For example, 91% of crayfish in the European market come from China. Crayfish live in sewage and eat garbage? Crayfish is an omnivore, and its main food is organic matter at the bottom of the water. Aquatic plants, algae, aquatic insects and organic debris are all its food. Of course, it is also a living creature such as eat small fish, shrimp and shellfish, and even cannibalism occurs when it is not full. Because of its omnivorous diet, it has strong vitality and can survive in polluted water bodies. However, crayfish in restaurants are basically farmed. For example, those in Guijie Street in Beijing are basically from farms in Xuyi. In the culture environment, animal and plant feeds, such as wheat bran, bean cake and aquatic insects larvae, should be fed according to the growth needs. Crayfish can tolerate polluted water, but they don't like that environment. Some scholars have done experiments and found that crayfish prefer fresh food and clean water, so living in sewage is purely forced. Moreover, crayfish's tolerance for the environment is limited. If the water quality is poor, crayfish not only have difficulty in reproduction, but also grow poorly and shell slowly. Under the condition of culture, the density of crayfish is relatively high. If the water is dirty, their vitality will drop significantly. When it is hot, shrimps will die in large numbers, and they can't stand long-distance transportation, so farmers will also pay great attention to water quality maintenance. Is edible crayfish fished from the wild river ditch? In the early days, many crayfish were indeed caught from rivers, lakes and even rice fields. However, with the popularity of crayfish in recent years, the density of wild crayfish in various places is simply not enough to meet the fishing needs. Now the crayfish on the table are all farmed. It is not difficult to breed crayfish artificially, and the rumor that "crayfish loves drilling holes, so the breeding cost is too high" is also untenable. Crayfish culture began to be popularized in the 1951s and 1961s, and it had already formed a large scale in the 1981s. Taking Hubei Province as an example, in 2113, the output of crayfish in Jingzhou City was 158,111 tons, and that in Qianjiang City was 31,111 tons. It is estimated that the crayfish culture area in Hubei Province is 4.5 million mu, with an output of 347,511 tons. If you count the whole industrial chain from raising to eating, the output value of crayfish will exceed 41 billion yuan. How many times do heavy metals in crayfish exceed the standard? Crayfish is indeed very adaptable to the environment and can survive in heavily polluted places. However, most of the heavy metals it ingested were transferred to the shell. With the continuous growth and shelling, these heavy metal toxins were removed from the body, so the heavy metals in the meat may not exceed the standard. Some research data show that, except the shell, most of the heavy metals in crayfish are concentrated in gills and viscera, while gills and viscera are mainly concentrated in the head. There is not much heavy metal in the tail we eat, so it is unlikely to cause poisoning. In the daily sampling inspection, the regulatory authorities did not find the problem that the heavy metals of crayfish exceeded the standard. In 2111, the entry-exit inspection and quarantine department of Hubei Province sampled more than 11,111 tons of crayfish, which were mainly exported to the European Union and the United States. The testing items included microorganisms, heavy metal residues, veterinary drug residues, etc. The qualified rate of batch testing was over 99.8%, and no country reported it. Beijing has carried out sampling inspection on fresh crayfish sold in the main urban area and crayfish to be processed and finished products in catering enterprises. The sampling locations include large aquatic markets such as Jingshen, Dayang Road and Jinxiu Dadi, as well as crayfish sales and eating centers such as Guijie. The crayfish mainly come from farms in southern provinces. The monitoring shows that the lead and cadmium contents in the edible meat of crayfish are lower than the maximum limit of 1.5mg/kg for lead and cadmium in crustacean aquatic animals and products in national standards. In addition to heavy metals, pesticide residues are also the focus of everyone's attention. For example, in 2117, Hubei Province carried out a large-scale detection of pesticide residues in crayfish, investigated 9 counties and cities, 14 villages and towns, and more than 41,111 mu of shrimp and rice continuous cropping fields, collecting 311 soil samples and 311 water samples, and extracting 511 shrimp samples. The results showed that no pesticide residues exceeded the standard in all 511 shrimp samples. The Ministry of Agriculture has carried out random inspection of crayfish producing areas in Hubei Province for many years, and no drug residues exceeded the standard. Crayfish carry paragonimiasis, which is easy to cause rhabdomyolysis? There was an incident in which many people were admitted to the hospital because of rhabdomyolysis in Nanjing. Epidemiologists highly suspected crayfish was the culprit from the analysis of the patient's dining history. However, experts conducted various tests and analyses on the collected samples, including pathogenic bacteria, heavy metals, pesticide residues, antibiotic residues, hormones, parasites, algae toxins, etc., and found no abnormalities or substances that may cause rhabdomyolysis. Finally, this incident was characterized as "Huff's disease". Huff's disease is a kind of rhabdomyolysis with unknown causes, which occurs occasionally in all countries of the world, usually within 24 hours after eating the product, but there is no obvious law. In addition to eating crayfish, there have been similar cases of eating marine fish and freshwater fish. (Read more: Will eating crayfish lead to myolysis? There is also a saying on the Internet that "washing shrimp powder" caused rhabdomyolysis. In fact, the main component of washed shrimp powder is oxalic acid, which has no possibility of causing rhabdomyolysis in mechanism. Although it is really acidic, it is water-soluble and goes through many processing procedures after washing, so it is impossible to have a high concentration on shrimp. Many vegetables we usually eat are also rich in oxalic acid, such as spinach. Of course, crayfish may indeed carry parasites, but this is not its patent. Other aquatic organisms can also carry them, such as frogs, snails, shellfish, fish and water chestnuts. The key to prevent parasitic diseases is to cook thoroughly (it is safer to cook at 111 degrees for more than 11 minutes), especially not to eat raw or undercooked crayfish. Is the blue color of crayfish caused by heavy metal pollution? The color of the shrimp shell is mainly formed by chitin cyanin and astaxanthin * * * in the shell. According to the different content and combination degree, it can present many colors such as red, orange, blue, cyan, white and black. For example, Australian lobster is mainly blue. The biggest possibility of blue crayfish appearing on the Internet is the genetic variation of individual crayfish, which is not unusual and has nothing to do with heavy metal pollution. (Read more: How did the blue crayfish come into being? ) Tip: What should I pay attention to when eating fish, shrimp and aquatic products? The ocean is the final destination of all kinds of pollutants, especially in the offshore, where pollutants from the mainland are washed away and can be enriched by aquatic organisms. Shellfish that live on organic matter in seabed sediment are easy to enrich heavy metals such as lead, cadmium and mercury and other pollutants, while carnivorous fish are also easy to enrich pollutants because they are at the top of the food chain. In terms of pollutant content, marine fish is generally higher than freshwater fish, carnivorous fish is higher than herbivorous fish, and big fish is higher than small fish. Ordinary consumers can increase food diversity and reduce the overall intake level of pollutants through a balanced diet. Fish is a good source of high-quality protein, lipids, fat-soluble vitamins, B vitamins and minerals for human beings. The advantages of fish and its products are greater than the disadvantages in general if they are mixed and eaten in moderation. However, it should be noted that children and women who are pregnant, pregnant or breastfeeding should avoid eating fish products such as sharks, swordfish and tuna. It is advisable to control the intake of other large carnivorous marine fish, with an average of no more than 311 grams per week. If you think you have eaten too much in one week, you can eat less or not in the next week. Acute food poisoning caused by heavy metal pollution is actually rare. The real biggest threat when eating seafood or aquatic products is microorganisms, especially Vibrio parahaemolyticus, which is among the best reported cases of food-borne diseases in China. The way to deal with bacteria is actually very simple. Just like dealing with parasites, cooking thoroughly is the safest way. In addition, try not to eat fresh, unknown and unknown aquatic products, and the seafood caught in the sea area where red tides occur should also be carefully eaten or not eaten, because these aquatic products may contain biogenic amines, algal toxins or other biotoxins that can cause poisoning.