Crab is a rare specialty in Qilihai. There are two geomantic treasures in Ninghe River in Tianjin, Qilihai and Jiyun Canal. Not only around Qilihai Lake and on both sides of Jiyun Canal are rich in "standing rice", but the two treasures of Ninghe River, "whitebait and purple crab", have been handed down from generation to generation. Whitebait is produced in Jiyun Canal, and purple crab is produced in Qilihai. The real top-grade purple crab is only produced in the "old field" and "official berth" of Xitangtuo Village in the center of Qilihai Lake. In the 1950s, the buyers of Beijing's "Eight Big Offices" all lived in Xitangtuo, and they all picked crabs that went out to sea first. They know three tricks for picking crabs, namely "look, weigh and pinch". The so-called "a look" is to look at the color of the crab first. The real purple crabs in old farms or official berths are purple-shelled golden claws, while the crabs in "Shangbozi" or other places are blue-brown with gray claws, which experts can know at a glance. The so-called "secondary weighing" is to weigh the weight in your hand again. Real purple crabs are heavy, while other crabs are much lighter. The so-called "three pinches" means finally pinching with fingers. The real purple crab pinches very successfully, and the stick is hard, which means that it is very substantial, while other crabs pinch soft, which means that it is very flat.
All crabs are covered with hard crustaceans, and the head and chest are fused together to form the head and chest, and the head and chest are covered with breastplates. Abdomen (commonly known locally as navel) is flat, women are round and men are triangular, so locals call it round navel and pointed navel. In ancient books, crabs are misunderstood as "heartless sons". If its abdomen is unfolded, a protruding intestine can be seen at the midline of its inner wall. The anus is open at the end of the abdomen. The crab has a pair of compound eyes with handles on both sides of its forehead. The compound eyes have a wide range of activities, and can stand upright or lie flat in the eye socket.
Although crabs grow in Qilihai Lake, they lay eggs in shallow water near the mouth of Bohai Bay. Every autumn, the "seven ups and eight downs" of the lunar calendar is its breeding and migration season. After a sexually mature female crab goes into the sea, she must molt once before mating and spawning. You can't mate with a male crab until you molt. After mating, the shell of the female crab gradually hardens and is ready to lay eggs. February 65438 to March of the following year is the peak period for crabs to mate and lay eggs. All crabs can mate and lay eggs under the condition of salinity of 8~33‰. After mating, eggs can be laid in about 7~ 16 hours when the water temperature is 9~ 12 degrees. A female crab with a weight 100 ~ 200g can lay 200 ~ 900,000 eggs at a time. When the temperature is suitable, the eggs can hatch into larvae after 1~2 months. Crabs only lay eggs once in their lives, and all the eggs are attached to their abdominal limbs. In the late spring or early summer of the following year, the females migrate to the estuary and the eggs hatch. At this time, they are all getting old and will die soon, and they haven't even had time to see their children.
Crabs have the special function of regenerating broken feet in order to protect their cars. Its significance lies in: repairing wounds and allowing lost organs to grow again. This phenomenon is very common in the animal kingdom, and crabs are no exception. After the crab's foot is cut by itself, a soft nodule grows on the surface of the residue within about six days. It is wrapped in a transparent chitin bag, which is called limb bud. In the next two or three weeks, limb buds grew rapidly and began to be segmented, and their epithelial tissues, striated muscle fibers, motor and sensory neurons also appeared one after another. After that, it entered a slow growth stage that lasted for several months. Finally, near molting, limb buds begin to grow rapidly again, with obvious segments. The joints between segments grow completely, and there are sensory hairs and thorns on the surface. Sensory nerves are embedded in sensory hairs, and tissue growth is completed here. After molting, the limb buds remove chitin sacs and form new feet. If the joint between the crab's foot and its body is artificially cut off, it always regenerates a complete basal node first, and then grows limb buds. This shows that the existence of the bottom node is an important condition for regeneration. From the phenomenon of crab's broken foot regeneration, it can be seen that the regeneration structure and function of crab are self-contained, and it forms a complete unity with self-cutting, which enhances the ability of animals to adapt to the environment and enables the population to survive and continue under long and harsh natural selection.
The average animal always moves forward or backward with its head as the center. But crabs are different. He has been crawling sideways, running around, fighting for food everywhere, and he is very overbearing. Why are crabs rampant? As we know, the crab mainly moves on the ground by its four pairs of feet. These four pairs of feet grow laterally from the chest to the left and right sides, and the joints of each foot cannot move freely, but bend downward. When a crab crawls, it first grabs the ground with a few steps, then sticks to the ground with other steps to push its body forward in the direction of step growth. Obviously, this movement can only be left or right, not forward or backward. However, in real life, how can light run rampant? Many times, we need to change the direction of progress, otherwise we will be at a loss once we encounter obstacles or the enemy's harm. What should we do? Fortunately, crabs have the ability to adapt to the environment, so that their feet are long and short, and they can change their direction as long as they exert different forces. If you watch carefully at the seaside, you will see many crabs crawling sideways, and they are trying to turn.
Crabs eat step by step. When it finds food, it first grabs the food with a pair of pincer-like claws and sends it to its mouth, then grabs the food with its second feet, submits it to the third pair of jaws, and then passes it to the big jaw for chopping. At the same time, let the first pair and the second pair of jaws protect the tiny food from being lost. Finally, the ground food is eaten and sent to its digestive stomach through the short esophagus. Crabs like to eat fish, shrimp, shellfish, snails, mussels and grains, and are omnivorous. It is particularly interested in animal carcasses, and even eats a stinky fish with relish. It often walks around tirelessly, eating a piece of stale meat. What is even more incredible is that this crab is so greedy that even his companion's body is worthy of it. If you see your partner hurt, instead of saving lives, it cruelly drags him over to feed his hunger. If you meet a soft-shelled crab that has just molted, it will take the opportunity to eat a lot. What a pity!
After being caught, the crab immediately spat out bubbles, as if begging for mercy and cursing the people who played tricks on it. It's really interesting. Why do crabs blister? It turns out that this is what happens when they breathe on land. Crabs are animals that breathe with their gills, which are hidden on the left and right sides under the breastplate. Usually it exchanges nitrogen and oxygen through the water flowing through the gill cavity. After leaving the water, it has to breathe directly in the air. So the air enters the gill cavity, mixes with the water left inside, and exhales, which will produce a lot of foam. As for the pattering sound, it is made when the bubble bursts.
The season for treating crabs is mainly in autumn. The "seven ups and eight downs" of the lunar calendar is the mature season for crabs and the peak season for fishing. The locals made reed foil from the reeds in Qilihai, woven them into crab houses, and put them in a big ditch with flow, waiting for crabs to drill. Crabs are about two months long in autumn, and thousands of pounds are caught every day.
Spring and dry season is a good time to dig crabs. In the first year, I don't go to the "seven ups and eight downs" crabs to steal the nest for the winter. At the turn of spring and summer in the following year, it was the lowest dry season in Qilihai, and both sides of reed ditch were covered with crab nests. Crab nests are straight, generally inclined to the ground level by about 10 degrees, and there is water in the depth. It is 20~80 cm long and 2~ 15 cm in diameter. When digging crabs, you can dig them out directly by hand when the nest is shallow, and you need a bamboo-handled crab hook made of 8~ 10 lead wire when the nest is deep. At this time, put the crab hook flat and close to the bottom of the crab nest, then straighten the hook tip, and then scratch the crab navel with the hook tip, and the crab will automatically climb out when it itches. You can fill a crab bag in a short time.
Crab shells are purple or blue-brown, but once cooked, they turn bright red or orange. What about this? Here's the thing. There are various pigment cells in the dermis of crab shell, and the wavelengths of light absorbed and reflected by them will show corresponding colors. Anthocyanin cells mostly exist in raw crab shells, but they are destroyed and decomposed at high temperature, while red pigment and yellow pigment cells are relatively stable and undamaged, thus making crab shells appear red or orange.
Although crab meat is nutritious and delicious, if it is not eaten well, it will be poisoned and have diarrhea. This is not because the crab meat itself is poisonous, but because the crab is not clean and refuses to let go of any stinky fish, dead shrimp and carrion, so that many toxic substances enter its stomach. So you must not eat its stomach, intestines, gills and other parts by mistake. Crabs often breed aquatic organisms harmful to human body. If crabs are eaten raw, they will inevitably be infected with parasitic diseases. So be sure to cook the crab thoroughly before eating. Pay attention to whether crabs are fresh when buying, especially river crabs, and be sure to eat them alive. Because crabs rot quickly after death, histidine produced is the most toxic.
The river crab was originally a special product of China, but it was discovered in the Thames in the early 1930s in England. According to the German report, German ships are anchored at the estuary of China. In early summer, the big-eyed larva of the river crab entered the cabin with ballast water through the ship's pumping pipe and arrived in Germany from China. In the past 70 or 80 years, it has been widely distributed in northern Europe.