Procambarus clarkii, also known as red swamp crayfish, Louisiana crayfish, or mudworm, is a species of Kambacidae crayfish native to freshwater bodies in northern Mexico, the southern United States, and the southeastern United States, but has also been introduced Elsewhere (North America and other continents of Europe), where it is often an invasive pest In Europe, P. clarkii has been on the Alliance's list of invasive alien species of concern since 2016 , meaning that the species cannot be imported, bred, transported, commercialized or intentionally released into the environment throughout the EU. Since being introduced to Nanjing, China, in the 20th century, they have spread widely throughout the Yangtze River Basin.
Diseases, disorders and predators
Crayfish are quite resistant to pests and pathogens, helping to explain the dramatic increase in density after their introduction. Systemic bacterial infections, especially those associated with Vibrio mimicus. Crayfish are highly resistant to the fungal disease Aphanomyces astaci, but are likely vectors of this disease in European crayfish.
Plants and animals can absorb heavy metals and metalloid elements from environmental soil and water. Some heavy metals, such as iron (Fe) and copper (Cu), are essential to the human body but are relatively toxic when used in large quantities. On the other hand, cadmium (Cd), lead (Pb), and arsenic (As) are non-essential metals or metalloids that are highly toxic to living organisms. These heavy metals and metalloids (toxic elements) often accumulate in freshwater animals. In fish and crayfish, toxic elements can be absorbed from the water through the gills and from sediments along the food chain. In particular, crayfish are considered excellent indicators of toxic contaminants in the environment. The hepatopancreas, not the muscles, is the primary organ where toxic elements accumulate.
Cd, As and Pb are particularly toxic elements in food and can accumulate in organisms. Cadmium is not biodegradable; it accumulates in organisms over a long period of time and has a long biological half-life in the human body. Cadmium is often reported to be harmful to human health. Cadmium toxicity can damage a variety of tissues, including the liver, kidneys, and lungs. In addition, cadmium can cause adverse effects in exposed organisms, including morphological disruption, physiological dysfunction, and biochemical changes. Lead is a cumulative poison that can damage the central and peripheral nervous systems, hematopoietic system, cardiovascular system, kidneys, liver, and male and female reproductive systems. It is a highly toxic carcinogen that exists in many different chemical forms and oxidation states. Hexavalent chromium (Cr(VI)) is a human carcinogen targeting the respiratory system, kidneys, liver and skin.
Toxic elements accumulate in crayfish, posing a threat to human health. Crayfish is loved by most people in China and other countries. Especially a favorite among young people, crayfish is consumed more frequently and is mainly produced in the Yangtze River Basin, including Hubei (Jianghan Plain) and Hunan provinces, which are the main areas for rice crayfish production.
The study selected 11 rice-shrimp polyculture farms in the main production areas of Hubei and Hunan provinces to collect crayfish and their breeding environment background, and analyzed four toxic elements (Cd, Cr, As and Pb) . The results pointed to lower concentrations of four toxic elements in the abdominal muscles than in the exoskeleton and hepatopancreas, which are not recommended for consumption. As an edible part, the content of toxic elements in abdominal muscles does not exceed the national safety threshold.
Crayfish as food
They were first used as food through a series of specific cooking methods. Due to its delicious taste, it is favored by more and more consumers, and consumer demand is growing rapidly. They quickly became a very popular aquatic food in China. In the past 20 years, it has been mainly farmed in rice fields, achieving the dual benefits of rice and crayfish. This is the reason why the area of rice and shrimp co-culture in China is increasing year by year. China's crayfish production continues to grow. In 2018, China's crayfish production reached 1.6387 million tons. Hubei and Hunan are the two major areas where rice and shrimp are co-cultured, and their annual output accounts for more than half of the total red swamp crayfish production. The middle and lower reaches of the Yangtze River consume more than 600,000 tons of red swamp crayfish every summer.
In the United States, crawfish are particularly popular in Louisiana, and crawfish boils are popular social gatherings centered around eating the crustaceans. Louisiana crawfish is usually cooked in a large pot with heavy seasonings (salt, chili peppers, lemon, garlic, bay leaves, etc.) and other items such as potatoes and corn on the cob.
Processing and food applications
The characteristics of the edible parts in relation to the total length and weight are used to determine the value and quantity of valuable parts during processing. Wash the whole crayfish and boil it in water for 3 to 5 minutes for human food
Effects of different cooking methods on the eating quality of crayfish and shrimp meat
Research shows that steaming (100°C), boiling (100°C), frying (160°C) and high-pressure steam (121°C) all have a bactericidal effect on crayfish. The color, taste and quality of steamed and boiled crayfish are better than those of fried and high-pressure steamed crayfish. Among the four cooking methods, the frying group had the highest cooking loss and the highest thiobarbituric acid value. The effects of the four heat treatments on the astaxanthin content in crayfish meat were significantly different. By comparing the contents of volatile flavor substances, it was found that steamed and fried crayfish contained more types of volatile flavor substances than the other two processing methods. When it comes to cooking crayfish, steaming helps maintain good eating quality. These results are helpful for crayfish processing and new product development.