The living habits and nutritional value of Chinese sturgeon (a treasure among fishes)

Chinese sturgeon (Acipenser sinensis) belongs to the order Acipenser, family Acipenseridae, and genus Acipenser. Commonly known as: catfish, sturgeon, lazi, sturgeon shark, tuna ("Erya"), tuna ("The Book of Songs"). English name: Chinese sturgeon, Green sturgeon.

Endangerment level: Vulnerable. China's national first-level protected wild animals.

IUCN (1996) EN. CITES (1997) Appendix II.

The sturgeons to which the Chinese sturgeon belongs all appeared in the Upper Cretaceous at the end of the Mesozoic Era, about 140 million years ago. There are now 25 species of sturgeons in the world, and they are concentrated in the northern hemisphere. There are 9 species in China: sturgeon and sturgeon in the Heilongjiang River, Sakhalin sturgeon in the Tumen River, small sturgeons and Siberian sturgeons in the Irtysh River in Xinjiang, naked sturgeons in the Ili River, and Acipenser dabrik and White sturgeon. Settling in the fresh water of the Yangtze River, the Chinese sturgeon is the southernmost species of sturgeon fish in the world. In modern times, it is distributed in coastal waters and major rivers such as the Yangtze River, Pearl River, Minjiang River, Qiantang River, and Yellow River. At present, the Yellow River and Qiantang River have all disappeared, and the Minjiang River estuary can occasionally be seen. The number of Pearl River is very small, and only the Yangtze River has a larger amount. It has been recorded in southwestern Korea and western Kyushu, Japan.

The Chinese sturgeon has a peculiar shape and is very different from ordinary fish. The body is fusiform, the head is large and elongated, and the front part of the eyes is flattened into a plow shape and turned upward. The mouth is on the ventral surface of the head, forming a transverse slit, and the mouth can expand and contract freely. The upper and lower lips have horny papillae. There are 4 small whiskers lined up in front of the mouth. The eyes are small. There are blowholes behind the eyes. The gill pores are large, and the gill membrane is connected to the isthmus. The gill rakers are short columnar, thin and pointed, with 14-28 members, usually around 18 members. The skin of juvenile fish is very smooth, without scales. There are 5 rows of large rhombus-shaped bone plates, 1 row on the back, 2 rows on the side and ventral side of the body. The number of bone plates on the side of the body is 24-37. The dorsal fin is located very far back and has 54 dorsal fin rays. -66. The upper lobe of the tail is longer and the lower lobe is shorter, forming a crooked caudal fin. The bones of the whole body are cartilage. The structure of the intestine is very peculiar, with 7-8 funnel-shaped spiral valves inside. The head and back of the body are blue-gray or gray-brown, the abdomen is gray-white, and each fin is gray. These characteristics indicate that sturgeons are lower bony fishes.

The Chinese sturgeon is a large anadromous fish, with the largest individual ever recorded weighing about 680 kilograms. Chinese sturgeon usually lives in the coastal continental shelf areas of the East China Sea and South China Sea, growing and developing in the sea. When the male fish grows to 9 to 18 years old, the body length is 170 cm and the weight is more than 50 kilograms, and the female fish reaches the first sexual maturity when it grows to 14 to 26 years old. These sexually mature Chinese sturgeons enter rivers from the ocean to breed between July and August. The spawning grounds are all in the upper reaches of the rivers. After the Chinese sturgeon enters the river, it must stay in the river for one year and arrive at the spawning site in October of the next year. During this year, the Chinese sturgeon does not always swim up the river, but swims and stops, sometimes lurking in potholes in the river without moving for several days. According to fishermen, when the south wind blows and the water level in the river fluctuates slightly, the sturgeons move upstream; when the north wind blows and the water level fluctuates greatly, the sturgeons lurk in the deep water of the river. The ancients have records that "the dragon comes out of the deep waters of the Yangtze River, Huaihe River, Yellow River, and Liaohe River" and "it also lives among the rocks and rapids." Chinese sturgeons travel more than 3,000 kilometers upstream in the Yangtze River, reaching the lower section of the Jinsha River, and breed in the 600-kilometer stretch upstream from Yibin City, Sichuan Province. The reproductive season is from early October to early November. After fertilization, the sturgeon eggs are washed away by the river water and adhere to the rocks at the bottom of the river. The seedlings hatch out one week later. The young fish swim down the river and arrive at the mouth of the Yangtze River in July of the next summer. They enter the ocean to grow and develop. When they grow up, they return to their birthplace to breed the next generation. After laying eggs, the broodstock and juvenile fish still return to the ocean to live, and after a few years return to the river for the next breeding trip. Sturgeons have great fecundity. One female Chinese sturgeon can carry 300,000-1.3 million eggs, but more than 90% of the eggs produced are eaten by fish such as copper fish and yellow catfish. Those who can survive Every little bit fell into the cracks of the rocks. However, the young Chinese sturgeons have very strong vitality. Once the fry hatch out, they will quickly float to the surface of the water and then swim to very shallow water. They seem to know that spawning is dangerous. Only 10% of the individuals that can grow up to mature and come back to breed again are born. 2-3% of the total.

The Chinese sturgeon is a carnivorous fish. The early juveniles living in the middle and upper reaches of the Yangtze River feed on chironomid larvae, dragonfly larvae, mayfly larvae and plant debris. The juvenile fish in the brackish waters of the estuary feed on shrimps. They feed on animals, crabs and small fish. The record of its feeding habits in "Compendium of Materia Medica" is: "It eats by opening its mouth to receive objects and letting them come in. If it eats but does not drink, crabs and fish will eat it by mistake." In fact, the Chinese sturgeon relies on the expansion and contraction of its oral membrane to inhale food. Most of its food targets are various small animals that live on the surface of the mud or are trapped in the mud. Chinese sturgeons basically do not eat during their entire migration and stay in rivers from the ocean. Therefore, the energy consumption of Chinese sturgeon in fresh water and the nutrients required for gonad development depend on the large amount of fat and other substances accumulated in the body before entering fresh water. Therefore, in fresh water, the body becomes thinner as it approaches maturity.

The Chinese sturgeon is an important large-scale economic fish. Sichuan fishermen have a proverb that "a thousand pounds of wax seeds is worth a thousand pounds of elephants". Before the 1970s, according to incomplete statistics, the annual catch in the Yangtze River Basin was about 400-500 individuals over 50 kilograms, and the output was between 60,000 and 80,000 kilograms. In recent decades, due to various factors, the number of wild individuals has decreased significantly, and it is now in a vulnerable situation. At the same time, the Chinese sturgeon has certain academic and scientific value. The Chinese government has listed the Chinese sturgeon as a national grade I wild protected animal.

In the early 1980s, after the construction of the Gezhouba Water Conservancy Project on the Yangtze River, the migration channel of Chinese sturgeons from the sea to the river for breeding was cut off, which had a serious impact on the survival of Chinese sturgeons. As early as the mid-1950s, when the Yangtze River Basin planning began, national leaders proposed the need to conduct research on related issues such as the impact of the construction of the Gezhouba Water Conservancy Project on fish migration and spawning grounds. At that time, a group of scientific and technological personnel and The leaders of the competent departments insisted on opening an opening in the dam and adding a 12-meter-wide fish passage facility - a fishway. Two scientists, Wu Xianwen and Cao Wenxuan, academicians of the Chinese Academy of Sciences, based on the rich scientific data accumulated by the Institute of Hydrobiology of the Chinese Academy of Sciences over more than 20 years of fish resource surveys in the Yangtze River and the "fish overcoming problems" carried out by the Institute of Hydrobiology, the University of Hydraulic and Electric Power over the past few years. The actual data of "flow rate capacity" and the series of compensation measures taken by sturgeon-producing countries such as the former Soviet Union, Europe and the United States to protect and increase their resources were reviewed and investigated. Withstanding the pressure of public opinion from all aspects of society, we resolutely proposed the "Gezhouba Hub" The construction will not have a significant impact on the spawning grounds of domestic fish." "The Gezhouba hub blocks the migration channel of the Chinese sturgeon, which has serious adverse effects on this fish and must be rescued." "Artificial breeding and release measures should mainly be adopted. Fish-passing facilities should not be built.” "Chinese sturgeons are large in size and have very strict requirements on water flow conditions when traveling upstream. What's more, compared to the wide river surface and rapid river water, Chinese sturgeons cannot find a 12-meter-wide fishway." Based on the natural environmental conditions and hydrological data of the Yangtze River, it is boldly inferred that after the construction of the dam, Chinese sturgeons may form new spawning grounds under the dam for natural reproduction. This was the "Gezhouba Fish Channel Dispute" that shocked the whole country at that time. Academician Wu Xianwen wrote this point of view into a proposal and submitted it to the central government, which was affirmed and adopted by the national leaders. This suggestion saved the country 53 million yuan in investment and became a big news at that time for scientists and democrats to participate in political discussions. Facts have proved that the Chinese sturgeons that entered the river to breed quickly adapted to the new environment and formed a new spawning ground in the lower reaches of the Gezhouba River.

After the construction of the Gezhouba Water Conservancy Project, although the Chinese sturgeon has a new spawning site, this breeding site is no longer what it used to be, from a 600-kilometer river section to only a 7-kilometer river section. With the launch of the Three Gorges Project, once the project is completed and put into operation, a large amount of water will be stored in the Three Gorges Reservoir in October, and the reservoir water level will increase to 175 meters, then the discharged water flow will be reduced by 41%. In this way, the Chinese Sturgeon Yichang Spawning Ground will be seriously affected, and the area of ​​the spawning river section will be reduced again. In order to protect the everlasting survival of this rare animal, China has been accelerating research on artificial breeding of Chinese sturgeons since 1980, and releases 10,000 to 20,000 artificially bred young sturgeons into the Yangtze River every year; the Fuzhou Municipal Government also in 2001 In December, 7,000 young sturgeons were released into the Minjiang River. According to expert estimates, in order to achieve the effect of restoring the resource proliferation of Chinese sturgeons, at least 100,000 Chinese sturgeons must be released into the Yangtze River every year. This must be supplemented by effective protection measures, and the fishing of Chinese sturgeons must be completely prohibited and strictly restricted. Use fish for scientific research to maximize the preservation of spawning sturgeon populations.

Chinese sturgeon is a high-protein, fatty fish. The protein content in muscle is 16.42-20.41% and fat is 3.05-4.32%; the protein content in liver is 10.31-16.26% and fat is 16.63-27.58%; the protein content in eggs is 24.90-29.70% and fat is 18.06- 24.00. Both muscles and eggs contain 17 common amino acids that can be measured. It contains 8 essential amino acids for the human body (in addition to tryptophan, which is destroyed by acid hydrolysis, there are also isoleucine, leucine, lysine, methionine, phenylalanine, threonine and valine) ; 2 semi-essential amino acids (arginine and histidine, both essential for infants); 8 non-essential amino acids (alanine, aspartic acid, cystine, glutamic acid, glycine, proline acid, serine, methane). Amino acids with high content in muscles include glutamic acid, aspartic acid, lysine, and leucine; amino acids with low content include histidine, methionine, and cystine; the content of other amino acids varies. The content of essential and semi-essential amino acids in female individual muscles accounts for 48.54% of the amino acid content, and eggs account for 48.80%; male muscles account for 49.105%. Due to its high amino acid content, the meat tastes delicious, the egg quality is also good, and it is rich in nutrients. The edible value of Chinese sturgeon's muscles, eggs, fins, etc. and the medicinal value of its swim bladder are the same as those of catfish and sturgeon. In Jiangsu and Shanghai areas, shad, spear (white sturgeon), scorpion (longnose sturgeon) and acupuncture (Chinese sturgeon) are listed as the four famous fish.

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