Recently, information about the price drop of crayfish has repeatedly hit the hot topics on the internet. Many crayfish enthusiasts in the comment sections exclaimed, "Happy!" "Now I can eat crayfish twice a day" ... However, some netizens expressed concern because they had heard: "Crayfish grow in stinky sewers, they like sewage, heavy metals exceed standards, and should not be eaten."
So, are crayfish really that dirty?
Crayfish Prefer Clean Water and Are Not Usually Contaminated with Heavy Metals
Many have heard claims that crayfish live in sewage and contain excessive heavy metals, which are harmful to health. However, these claims are not true.
Firstly, crayfish are not suited to living in sewage. Nowadays, crayfish are typically raised through standardized artificial farming methods, with the breeding process involving enhanced cultivation of shrimp seedlings to continually expand farming scale. Proper fertilization and cleaning of the water are necessary during the farming process to ensure the transparency and cleanliness of the water in the farming area, thereby maintaining clean water quality.
Experiments have also shown that crayfish not only do not prefer high concentrations of ammonia-type sewage but actively avoid it when concentrations reach a certain level. Failure to avoid such water can lead to abnormal behavior and even death. This indicates that crayfish also prefer clean water sources, and sewage is not conducive to their survival and reproduction.
Secondly, regarding the issue of heavy metal content in crayfish.
Researchers have detected the heavy metal content in different parts of crayfish, with results showing significant differences. The heavy metal element content in the abdominal muscle of crayfish is significantly lower than that in the head, with the general trend being head > shell > claws > abdominal muscle. This is because the detoxification and excretory organs such as the liver, kidney, and pancreas of crayfish are located in the head, and these organs can produce a large amount of metallothionein to bind heavy metal elements. Therefore, heavy metal elements are more likely to concentrate in the head of crayfish, and the shell is also an important part of crayfish for handling heavy metals.
So, if you're really concerned about heavy metals, you can avoid eating the heads of crayfish.
It should be noted that the heavy metal content of crayfish is closely related to their living environment. If standardized farming practices are followed and water quality is maintained, the safety of crayfish meat can be ensured. The heavy metal content in the edible parts (abdominal muscle) of standard crayfish on the market is within safe limits and can be consumed with confidence.
Nutritional Value of Crayfish
Crayfish, originally from North America, have become an important freshwater aquaculture species in the middle and lower reaches of the Yangtze River in China. Eating crayfish has become a growing dietary preference for many people. As long as crayfish are purchased through proper channels, there is no need to worry about heavy metal residues. Crayfish are also nutritious, let's take a look.
Crayfish contain 19% protein, which is easily digestible and absorbable high-quality protein. The fat content is only 1.1%, and 100 grams of crayfish contain only 90 kilocalories, which is lower in calories than eating one large apple. This high-protein, low-fat, and low-calorie delicacy is suitable for those who need to lose weight.
Crayfish are rich in zinc, with a content of 2.79 milligrams per 100 grams. Eating 100 grams of crayfish can meet 22% and 37% of the daily zinc requirements for men and women, respectively. Zinc deficiency can lead to picky eating, and severe cases can lead to pica, affecting brain function, wound healing, susceptibility to respiratory infections, inducing ADHD, affecting male fertility, hair loss, rough skin, and epithelial keratosis.
Crayfish are rich in selenium, with a content of 39.36 micrograms per 100 grams, which is twice that of Chinese shrimp and nearly five times that of pork tenderloin. Eating 100 grams of crayfish can meet 66% of the daily selenium requirements for the general population. Selenium can protect cardiovascular and myocardial health. Selenium deficiency can lower immunity, cause growth retardation, neurogenic visual impairment, and severe deficiency can induce Keshan disease.
The retinol content is 77.6 micrograms per 100 grams, which can help alleviate visual fatigue, maintain normal visual function, and protect the eyes. As you can see, crayfish are quite nutritious! However, if cooked improperly, eating crayfish can lead to weight gain, which we'll discuss later.
Four Things to Note When Buying Crayfish
Recently, crayfish have been gradually appearing on the market. What should you pay attention to when buying crayfish to ensure you get good ones?
It's best to buy live crayfish because the most important organ of crustaceans is a structure called the hepatopancreas, which secretes digestive enzymes to digest food and also absorbs and stores fat. Once crustaceans die, it becomes a source of rapid decay. Enzymes will destroy the small tubes in the glands and spread to the muscles, making them mushy and soft, and microbial growth will increase. Moreover, high summer temperatures favor bacterial growth. If you need to store them at home for some time, it's best to store them at 0°C, not exceeding 11 days; under 4°C refrigeration conditions, it's recommended to consume fresh crayfish within 8 days, and if they are refrigerated immediately after death, they can be stored for up to 4 days. However, for taste and safety considerations, it's best not to push it too far. Buy crayfish and cook them right away to ensure freshness. Frozen crayfish tails are usually processed from live crayfish and can be safely cooked. However, it's advisable to buy a small quantity at a time because prolonged freezing in a household refrigerator can toughen the meat and degrade the taste.
Fresh crayfish have a distinct odor, and if they smell fishy, sour, or ammonia-like, they are not fresh.
When purchasing lobster, it's best to buy farmed lobsters through formal channels rather than wild ones.
Cooking suggestions for lobster:
Boiling lobster in water can release a scent similar to berries or popcorn, and it tastes slightly sweet. If cooked with the shell on, the flavor is usually better because the shell retains the flavor of the meat and contains protein, sugars, and pigment molecules that enhance the taste of the meat near the shell.
It's also important to pay attention to the cooking method. Lobster is indeed high in protein and low in calories, which can be helpful for weight control. However, cooking methods should also be considered. Eating spicy crayfish, deep-fried lobster tails, or lobster cooked in oil regularly may lead to weight gain. In comparison, steamed lobster or lobster with garlic would be healthier choices.
Who should eat less or avoid lobster?
Lobster has a purine content of 174 milligrams/100 grams, making it a high-purine food. It's best to avoid it if you have gout or hyperuricemia. Some people like to pair lobster with beer, which can easily trigger gout attacks.
Lobster has a high cholesterol content of 121 milligrams/100 grams, which is 2.2 times that of pork tenderloin. People with high cholesterol levels should eat lobster sparingly or avoid it.
Tropomyosin is a major allergen in crustaceans. If you're allergic to other shellfish, it's best to avoid lobster as well. Allergic reactions can cause symptoms such as rash, diarrhea, asthma, shock, and even life-threatening situations.
Such as asthma, kidney disease, or those taking statins to lower blood lipids should consult their doctor before consuming lobster. In summary, if you only eat the lobster tail, you can rest assured; but if you enjoy sucking the head, it's best to eat less!
References:
[1] Wang Wenzhong. "Exploration of the reproductive habits and aquaculture management of crayfish." Fisheries Enrichment Guide, 2020, No.529(01):45-47.
[2] Chen Ting, Zhang Lei, Tang Jianqing, et al. "Selection of juvenile and sub-adult Macrobrachium nipponense for different ammonia concentration water environments." Resources and Environment in the Yangtze Basin, 2011, 20(10):1186-1190.
[3] Sui Ke, Hang Wei. "Research on the content and distribution of heavy metals in crayfish." In: Proceedings of the 20th National Conference on Molecular Spectroscopy of China Optical Society, Chinese Chemical Society, and China Optical Society Spectroscopy Professional Committee. 2018:2. DOI:10.26914/c.cnkihy.2018.017662.
[4] Quan Qingguo, Zhang Zewei, Chen Ming, et al. "Research progress on the comprehensive utilization of crayfish." Food Research and Development, 2019, 40(03):213-219.
[5] Yang Yuexin, Ge Keyou. "Comprehensive Nutrition Science Encyclopedia of China, 2nd Edition (Volume II)." People's Medical Publishing House, 2019.
