The living habits and nutritional value of paddlefish (the longest freshwater fish)

White sturgeon (Psephurus gladius) belongs to the order Acipenseriformes, family Acipensidae, and genus Psephurus. Commonly known as: elephant fish, elephant trunk fish, swordfish, sturgeon fish, pipe fish, it was called tuna in ancient times. English name: Chinese paddlefish.

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

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

The body is long and fusiform, with the front part slightly flattened, the middle part thick, and the rear part slightly flattened laterally. The head is extremely long, more than half the body length, and is covered with plum blossom-shaped traps. The snout is sword-shaped, particularly elongated, with a narrow and flat front end and a broad and thick base. The ventral surface of the head of the snout can be freely expanded and contracted. There is a record in ancient books that "the mouth of tuna is under the jaw and the cartilage of the long nose is the same", which succinctly summarizes the ecological characteristics of paddlefish. There are small, pointed teeth on the upper and lower jaws; a pair of short, short rostrums located on the ventral surface. Eyes are small. The entire surface of the head membrane is densely covered with many fine plum blossom spots of sensory nerve cell tissue. The gill openings are large and the body is smooth and scaleless. There are 8 prismatic scales on the upper lobe of the caudal fin, extending backward to the upper lobe of the caudal fin. The dorsal fin starts behind the pelvic fin and is composed of unbranched fins. The caudal fin is crooked, the upper lobe is well developed, and the front edge has a row of spinous scales. The intestine is short and has 7-8 spiral valves in the intestine. The head, body back and tail fin are blue-grey, and the abdomen is white.

White sturgeon is a semi-anadromous migratory fish. It inhabits the middle and lower layers of the main stream of the Yangtze River, and occasionally enters large lakes along the river. Large individuals mostly inhabit the deep water channels of the main stream. They are good at swimming and often swim in the vast water layers of various sections of the Yangtze River. Young fish often go to tributaries and rivers. They forage in harbor channels and even in the brackish waters of the Yangtze River Estuary. It is still unclear whether the white sturgeon needs to be fattened and grown in the sea like the Chinese sturgeon; but based on the analysis of the existing data, it is not certain that it is a fish that migrates to rivers and seas. White sturgeon is a large and ferocious fish. Both adults and juveniles feed on fish as their main food, and also eat small amounts of shrimps, crabs and other animals. The paddlefish is also a large fish. The age of first sexual maturity is 7-8 years old. The length of an individual is generally about 2 meters and the weight is more than 25 kilograms. According to the records of the famous zoologist Professor Bingzhi more than 50 years ago, a 7-meter-long individual weighing several kilograms was captured in Nanjing. So far, it is still the world's longest record of freshwater fish body length. Sichuan fishermen also have a saying of "a thousand catties of lazi (Chinese sturgeon) and a thousand catties of elephants (white sturgeon)". The reproductive season of white sturgeons is about March to April. The spawning sites are located above Luzhou, Sichuan Province. The water flow rate is about 0.49 m/s, the water depth is less than 10 meters, and the bottom is mostly rocks or pebbles. It is relatively concentrated. The spawning grounds are in the Yangtze River section near Jiang'an County and the Jinsha River section near Baishu Creek in Yibin. The mature eggs are gray-black and large. The eggs drift with the water and develop. The young fish reach the Yangtze River estuary for fattening and growth.

White sturgeons are distributed in the upper and lower reaches of the main stream of the Yangtze River, and can also survive in the brackish and fresh water waters of the estuary. It has been found in the Qiantang River in Zhejiang Province in the past, and it may have entered by bypassing the Yangtze River estuary. The annual output is about 25,000 kilograms. In the past decade, due to overfishing and other reasons, the resource has been declining and is now endangered.

Paddlefish are large in size, with juicy meat that is rich in fat and protein. The protein content in muscle is 17.18% and fat is 5.64%; the protein content in liver is 8.71% and fat is 8.20%; the protein content in ovary is 13.47% and fat is 15.42%. Both muscles and eggs contain measurable 17 common amino acids, and the contents of various amino acids are the same as those of Chinese sturgeon. Due to its rich nutrition, it has always been regarded as an edible treasure. In Jiangsu and Shanghai, shad, spear (white sturgeon), catfish and beetle (Chinese sturgeon) are listed as the four famous freshwater fish. In addition, the medicinal value of white sturgeon is also the same as that of Chinese sturgeon.

The paddlefish first appeared in the Cretaceous period (more than 100 million years ago). There are only two species of paddlefish in existence today, which are distributed in the Yangtze River in Asia and the Mississippi River in North America. The main reason is that due to the drastic environmental changes caused by the Quaternary Ice Age in paleogeology, the originally widely distributed paddlefish disappeared in many places. Only two species exist in the above two rivers that still have basic living conditions. remain. The paddlefish, a relict animal that survives its life after death, is extremely valuable in scientific research; in addition, the number of existing populations is extremely small. For this reason, the Environmental Protection Commission of the State Council listed it as a class of precious and rare animals under key protection in the "List of Key Protected Wild Animals" issued twice in 1983 and 1987. Although the scientific research department is currently conducting artificial breeding research, before large-scale artificial breeding is possible, the killing of parent and juvenile fish must be strictly prohibited, and the return of young sturgeons to the rivers must be vigorously encouraged to protect and save this rare and endangered species.

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