Crayfish is a kind of crustacean that lives in fresh water. Its scientific name is Procambarus clarkii, also known as red crayfish or freshwater crayfish. Procambarus clarkii is the most widely distributed invasive species among crustaceans. Procambarus clarkii has an absolute competitive advantage in the local ecological environment because of its omnivorousness, fast growth and strong adaptability. Its feeding range includes aquatic plants, algae, aquatic insects and animal carcasses. When food is scarce, they also kill each other. Procambarus clarkii has become an important economic breed in China. In the process of commercial farming, it is necessary to prevent escape, especially to enter untouched original ecological water bodies. Its destructive harm to the ecological competitive advantage of local species has been widely reported in the world and should be paid great attention to.
Crayfish is a kind of crustacean that lives in fresh water. Its scientific name is Procambarus clarkii, also known as red crayfish or freshwater crayfish. Northeast China is called Lashou. Taxonomically, the status of Procambarus clarkii is: Arthropoda, Crustacea, Decapoda, Reptiles, Enterobacteriaceae, Procambarus clarkii.
The origin of crayfish
Crayfish is native to Louisiana in the southern United States. 19 18, Japan introduced crayfish from the United States as bait for raising bullfrogs. According to some data, China did not produce crayfish in the past, and the origin of crayfish dates back to World War II. Crayfish (the predecessor of crayfish), which can be seen everywhere in Japan, has been transported to the Japanese military station in batches to purify the water after a series of genetic modification. The improved crayfish has stronger adaptability and reproductive ability to highly corrupt water bodies, especially to mineral poisoning water bodies. Japanese declassified archives show that crayfish carry paragonimiasis and black gill disease in eutrophic and anoxic water almost all their lives, but the mortality rate is close to normal. During World War II, crayfish was introduced into China from Japan, and now it has become an important freshwater shrimp resource in China, widely distributed in the middle and lower reaches of the Yangtze River.
The protein content of crayfish is relatively high, accounting for about 16%-20% of the total, and the fat content is less than 0.2%. The contents of trace elements such as zinc, iodine and selenium in shrimp meat are higher than those in other foods. But a very important nutrition of crayfish may be overlooked by many people, that is astaxanthin, which mainly exists in the yellow of shrimp head and the red substance on shrimp shell. Most cooking methods may be lost, because astaxanthin is a strong antioxidant, so it is easily oxidized. In addition, crayfish can also be used as medicine, which can eliminate phlegm and relieve cough and promote postoperative wound healing.
growing environment
From June to August every year, crayfish is the most "plump" time, and it is also the best time for people to catch and enjoy it. Green, shallow beach, this water area is where Lao Gan often catches lobsters.
Shrimp farmers say crayfish like to live in clean places, such as sewers, where crayfish will not grow up.
Why can scarlet crayfish survive and reproduce in dirty mud, while reddish prawns are not easy to survive even in clear water?
Scientific research has proved that the content of astaxanthin in the body is positively related to its ability to resist the harsh external environment, which means that the higher the content of astaxanthin in the body, the stronger its ability to resist the harsh external environment. The content of natural astaxanthin in Bordeaux crayfish is several times that of prawn. Therefore, crimson crayfish can survive and reproduce in dirty mud, while reddish prawns are not easy to survive even in clear water.
Crayfish are omnivores, mainly eating plants. Small fish, shrimp, plankton, benthos and algae can all be used as its food. The breeding ability of crayfish is not strong, and crayfish breed 1 time a year.
Alien invasive species
Procambarus clarkii is the most widely distributed invasive species among crustaceans.
Procambarus clarkii has an absolute competitive advantage in the local ecological environment because of its omnivorousness, fast growth and strong adaptability. Its feeding range includes aquatic plants, algae, aquatic insects and animal carcasses. When food is scarce, they also kill each other. Procambarus clarkii can endure the dry season as long as four months, and can also adapt to the brackish water environment where bitter and salty water meet at the estuary. In rainy season, Procambarus clarkii can migrate for several kilometers to find new habitats. When feeding, you can use its strong claws to cut off the tender stems of plants; In recent years, Procambarus clarkii has become an important economic breed in China. In the process of commercial farming, it is necessary to guard against escape, especially entering the original ecological water body with few people. Its destructive harm to the ecological competitive advantage of local species has been widely reported in the world, which should arouse our great attention.
Morphological characteristics of crayfish
The body is large and cylindrical, the shell is firm and thick, the head and breastplate are slightly flat, the front edge does not heal with the front plate of the mouth, and the side edge does not heal with the abdominal shell of the chest and the base of the chest limb, except for crayfish. The neck groove is obvious. The antenna 1 is short and small, Shuang Bian. The second antenna has grown scales. All three pairs of jaws and feet have external limbs. The feet are all single-branched, and the first three pairs are chelated, among which 1 pair is particularly strong, so it is also called crayfish. The last two pairs of feet are simple claw-shaped. Gills are filamentous gills.
Lobster head has three pairs of tentacles, thick near the head and small and sharp at the top. A pair of tentacles on the outer edge of the head are particularly thick and long, generally longer than the body1/3; Between a pair of long tentacles are two pairs of short tentacles, which are about half the length of the body. When resting and crawling normally, all six tentacles extend forward. If frightened or attacked, two long tentacles will bend to the tail to prevent the tail from being attacked.
There are five pairs of feet in the chest, 1-3 pairs of feet end with pliers, and 4-5 pairs of feet end with claws. The second pair of walking feet are particularly developed and become very large claws. The claws of male lobsters are more developed than those of female lobsters, and there is a bright red film on the front outer edge of male lobsters, which is very conspicuous. Females do not have this red membrane, so this is an important feature that distinguishes males from females.
Morphological characteristics of crayfish
There are five powerful tail fans at the tail. When the mother shrimp crawls or is attacked during the incubation period, the tail fan bends inward to protect the fertilized egg or young shrimp from injury.
Crayfish, like other crustaceans, must take off their crustaceans to complete the mutation growth.
The molting of crayfish is closely related to water temperature, nutrition and individual development stage. Larvae usually molt once every 4-6 days, and young shrimps that leave the mother's body and enter the open water once every 5-8 days, and the molting interval of young shrimps in the later period is usually 8-20 days. When the water temperature is high, the food is sufficient and the development stage is early, the molting interval is short. Sexually mature females and males generally molt 1 ~ 2 times a year. Crayfish with a body length of 8 ~ 1 1 cm can grow 1.3cm each time they molt. The molting of crayfish mostly happens at night, and sometimes it can be seen during the day in the case of artificial breeding. According to the activity and food intake of this shrimp, its molting cycle can be divided into four stages: molting interval, molting prophase, molting period and molting anaphase.
How to choose a good lobster according to its shape
Red, soft-skinned and dragged shrimps are not fresh, so try not to eat them. Deteriorated shrimps are inedible. Pick the shrimp line on the back of the shrimp and don't eat it.
The most important thing is to choose crayfish. The best time for crayfish is from May to 10. It is yellow all over, full of meat and fat, and even the three sections on its big claws are full of elastic teeth and snow muscles from beginning to end.
See if crayfish is clear water or muddy water. Look at the back, bright red and clean, acceptable. Then look at the fluff on its abdomen and the hair on its claws. If it is white and neat, it is basically raised in clear water.
After all, crayfish are humus-eating corpses, and bacteria and toxins will only accumulate in the body. So, try to buy lobsters that have just grown up. Old lobsters are red, black or red with metal gray, while crayfish are bright and beautiful, with a natural and healthy luster. If you just touch its shell with your hands, it will be hard and hard, and it will be old. I just grew up and changed my shell to be as elastic as a nail.
Crayfish are omnivores, mainly eating plants. Small fish, shrimp, plankton, benthos and algae can all be used as its food. The breeding ability of crayfish is not strong, and crayfish breed 1 time a year.
Crayfish have a very strong viability. Besides Japan and China, Europe and Africa also occupy its territory, so it has become a world-class invasive species and a world-class delicacy. In Europe, Africa, Australia, Canada, New Zealand and the United States, people eat crayfish. Louisiana claims to produce 90% of crayfish in the world, and locals eat 70% of them. The "success" of crayfish in the world is partly attributed to its tolerance to polluted environment besides some advantages in morphology and habits. In scientific research, organisms that are very sensitive or tolerant to pollutants are often used as indicators of whether the environment is polluted. Crayfish is such a potential indicator.
Scientific research has proved that the content of astaxanthin in the body is positively related to its ability to resist the harsh external environment, which means that the higher the content of astaxanthin in the body, the stronger its ability to resist the harsh external environment. Crayfish can't produce astaxanthin by itself, mainly through food chain-edible microalgae, and accumulate in the body to produce super antioxidant capacity. Astaxanthin can effectively enhance the ability of crayfish to resist harsh environment and improve their reproductive ability. Therefore, astaxanthin is a powerful guarantee for the tenacious vitality of crayfish. Without these microalgae containing astaxanthin, crayfish can hardly survive. This also gives people some misunderstandings: crayfish must live in a dirty environment.
In terms of eating habits, crayfish prefer to eat mud at the bottom of the river and eat dead small fish or other aquatic organisms.
Crayfish is an omnivore, which mainly feeds on organic debris. It can eat all kinds of cereals, cakes, vegetables, terrestrial grasses, aquatic plants, epiphytes, zooplankton, aquatic insects, small benthos and animal carcasses, and also likes to eat artificial compound feed. At the temperature of 20 ~ 25℃, crayfish can eat 3.2% of its own weight, bamboo leaves 2.6%, water peanuts 1. 1%, bean cakes 1.2%, artificial feed 2.8%, fish 4.9% and earthworm 65438 every day and night. It can be seen that crayfish like to eat animal substances. In natural water, because of its poor predation ability, plant components account for more than 98% in the food composition of this shrimp. Some people mistakenly believe that crayfish can prey on fry and fish species, which is very harmful to aquaculture. In fact, under normal circumstances, crayfish have no ability to prey on fry and fingerlings. Although crayfish can't catch fast-swimming fish, it can prey on sick individuals, zooplankton, algae and plants floating on the water.
1, benthos
Lobsters like to inhabit hidden objects such as aquatic plants, branches and crevices. Shrimp lies in the daytime and comes out at night. It doesn't like bright light.
2. hydrophilicity
Lobsters have a strong tendency to flow, like fresh water and flowing water, go upstream and live in groups.
3. enterprising
Lobsters are aggressive by nature. When they lack feed or struggle to survive in caves, they often bully the weak and fear the hard. Larvae has strong regeneration ability, and this self-cutting and regeneration behavior is a protective adaptation.
4. Digging habits
Lobsters like to dig holes and are good at digging holes.
① Digging depth and speed
The depth of lobster digging hole is the key factor to determine its harm degree. Lobsters dig holes quickly, especially in the new living environment. In sandy soil, most lobsters dig new holes with a depth of more than 30 cm.
② the location of lobster hole
Lobster caves are usually located in the horizontal plane, generally 20 cm above and below the water surface, with the largest number of lobster caves. Lobster caves are located on the waterfront, on the slopes in the water, at the bottom of shallow water pools, and concentrated in places with lush aquatic plants.
③ Influence of living environment on lobster burrowing.
The sedimentary conditions of water body have obvious influence on lobster burrowing. But no matter what kind of living environment, the number of lobsters digging holes in the breeding season has increased obviously.
Distribution range and use of crayfish
Crayfish are widely distributed all over the world. It is mainly divided into three families, including Carabidae, Procambarus (or Crab and Shrimp), Octopus (or Procambarus), with dozens of genera and more than 400 species. Procambarus clarkii is mainly distributed in Madagascar, Australia, New Zealand, Chile, New Guinea and other places belonging to Gondwana, with a large size, and the heaviest individual found in Tasmania reaches 6 kg.
Procambarus is mainly distributed in Europe and western North America, and the genus of medium size and great economic significance is Pacific crayfish. The crayfish family is mainly distributed in eastern North America and East Asia, and its size is relatively small. The economically significant species is Procambarus clarkii, especially Procambarus clarkii, which accounts for 70% to 80% of the world's freshwater lobster production.
Distribution range and use of crayfish
Crayfish are widely distributed in various water bodies, especially in still water ditches, shallow lakes and ponds. It shows that prawn has strong adaptability to eutrophication and anoxia of water body. Generally, the dissolved oxygen in water is above 3 mg/L, which can meet its growth needs. When the dissolved oxygen in water is insufficient, shrimps often climb to the surface of water to breathe or deflect their bodies with the help of weeds, branches, stones and other things in water, so that gill cavities can breathe on the surface of water, and even climb to land to breathe with the help of oxygen in the air. Shrimp can live for more than a week without water.
Crayfish is an out-and-out "exotic". Crayfish, native to North America, is an important species of freshwater shrimp culture in the United States. 19 18 years, Japan introduced crayfish from the United States as bait for raising bullfrogs, and crayfish proliferated in a large area in Japan. During World War II, crayfish were introduced into China from Japan and began to be cultured in Nanjing and suburban counties of Jiangsu. After a long period of expansion, the population has increased and the living space has expanded. Now it has become an important freshwater shrimp resource in China, widely distributed in the middle and lower reaches of the Yangtze River in China.
Crayfish in China are mainly distributed in the middle and lower reaches of the Yangtze River, such as Jiangsu, Hubei, Jiangxi, Anhui and other places, and grow in rivers, lakes and other water bodies, with a number of more than 60,000 tons. Jiangsu is a key province for processing and exporting freshwater lobsters. There are more than 60 processing enterprises in the province, and the annual export volume of processed lobsters is about 6,000 tons, accounting for about 90% of the total export volume in China.
Main uses of crayfish
In recent years, crayfish are very popular in Beijing, Nanjing, Shanghai, Suzhou, Wuxi and other places, with annual consumption of 20,000-30,000 tons. The consumption of crayfish exceeds the demand.
Crayfish has strong adaptability to the water temperature. This is consistent with its geographical distribution across tropics, subtropics and temperate zones. Its temperature adaptation range is 0℃ ~ 37℃. In the Yangtze River valley, if there is water outside in winter, it can still survive if it is frozen, but the optimum temperature range of crayfish is 18℃ ~ 3 1℃.
Main applications
Crayfish is made into many kinds of dishes because it is bigger, fleshy and delicious than other freshwater shrimps. The famous spicy crayfish (Ma Xiaoer) is a common food, which is widely welcomed.
Because most crayfish have very strong anti-pollution ability, they can still survive in water containing highly polluting toxins. In addition, most crayfish are opportunists (such as crayfish, red crayfish and other large freshwater lobsters), and even feces or animal carcasses have become the focus of their dishes. Keeping in the aquarium can also effectively remove fish manure and moss, which has made great contributions to the improvement of hydrological environment.