We have a new kind of Yangtze River elf! Xinhua News Agency reported on May 15 that mainland researchers found a new species of fish in an underground river in a karst cave while conducting field surveys in the Wujiang River basin in the upper reaches of the Yangtze River, naming it "Guiyang goldenrod".
The discovery of "new" fish in the Yangtze River is gratifying, and it is also gratifying that there is good news for the "old" fish in the Yangtze River: three years after the implementation of the 10-year fishing ban policy in the Yangtze River, the populations of native fish in some waters of the Yangtze River basin have been observed to have recovered to a certain extent!
Figure 1: Guiyang catfish, a newly discovered fish by mainland researchers in the upper reaches of the Yangtze River (source: Xinhua News Agency video screenshot)
01 The unavoidable role of the "old" fish in the Yangtze River - migratory fish
Many of the native fish species in the Yangtze River are migratory fish, and their special living habits make them particularly vulnerable to human activities such as overfishing, water pollution, water conservancy projects, and shipping. So what are migratory fishes?
According to the purpose of survival, the migration of fish can be divided into three categories:
▶ Reproductive migration: The periodic movement of fish in response to the need to reproduce offspring.
▶ Forage migration: The periodic movement of fish for the purpose of feeding.
▶ Vertical migratory fish move up and down in the water column due to factors such as protection from light, predators, and temperature (only occur in the ocean).
According to the migration direction, the migration of fish can also be divided into three categories:
List of migratory fish types (Tabulation: Hu Kai)
Note [1]: The migration of rivers and lakes for the purpose of reproduction is relatively complicated, and those four major fish living in the lake, including herring, grass carp, silver carp and bighead carp, enter the Yangtze River from the lake to breed, which can be regarded as the migration of rivers and lakes.
02 Analodromous migratory fish
The famous "Three Fresh Foods of the Yangtze River": anchovy, saury (swordfish) and puffer fish (Oriental pufferfish), and the Chinese sturgeon, known as the "giant panda in the water", when they migrate during the breeding season, the way of migration is called anadromous migration; The adults of these fish generally live in the ocean (some populations of swordfish live in freshwater for life, and are smaller, commonly known as "lake knives"), and when the breeding season comes, they will swim upstream, enter freshwater to spawn and reproduce, and return to the ocean after completing reproduction; The hatched fry feed and fatten in fresh water for a period of time before moving down the river into marine life.
Figure 2: One of the three fresh "knife fish" in the Yangtze River (source: Hubei News video screenshot)
Figure 3: One of the three fresh fish in the Yangtze River, the "Oriental pufferfish" (source: Xinhuanet)
The Yangtze River is an important breeding ground for these migratory fish, and for example, the Yangtze saury (migratory ecotype swordfish) has been difficult to form a fishing flood for a long time due to factors such as overfishing and water conservancy projects in the Yangtze River.
Before and after the implementation of the fishing ban, the number of saury fish rebounded, and reappeared in some sections of the river that had been extinct for many years. For example, in Shanghai's Chongming District, a fishing ban was carried out long before the Yangtze River fishing ban was implemented, and in March 2021, during a fish monitoring in the Yangtze River waters, researchers caught nearly 200 kilograms of saury in one net. In February 2023, the Ministry of Agriculture and Rural Affairs announced at a press conference that saury is now able to migrate back to the waters of Dongting Lake, which has reached the farthest area that saury can migrate to in history.
03 Migratory fish falling into the sea
Another type of migratory fish in the Yangtze River is the sea migration, the most typical of which is the Japanese eel, commonly known as "white eel" and "eel". In contrast to swordfish and shad, Japanese eels breed in the ocean, and sexually mature Japanese eels swim to the deep sea near the Mariana Trench in the Philippines for the only time in their lives before dying.
Newly hatched young eels are called willow leaf eels; After metamorphosis, the willow leaf eel will grow into a glass eel that is close to the appearance of an adult eel, migrate to the estuary of the Yangtze River and other rivers leading to the sea, and then go up to the river. Glass eels develop into yellow eels in freshwater, where they grow and fatten for several years until they reach sexual maturity and return to the ocean to breed.
Figure 4: The development process of the Japanese eel (Source: Wikipedia)
Because of its fatty and delicious meat, Japanese eels have been overfished and are now listed as endangered on the IUCN Red List. The artificial breeding technology of Japanese eels is very immature, so the "cultured" Japanese eels we see in the market are actually wild eel seedlings caught in the Yangtze River, Qiantang River and other estuaries and then fattened and raised in an artificial environment.
图五:日本鳗鲡(来源:Wikipedia)
With the implementation of the 10-year fishing ban, it has become illegal to harvest wild Japanese eels in the main stream of the Yangtze River and in large lakes that run through the Yangtze River. As for the fishing of eel fry in the estuary, the current law also has strict quotas on the fishing time, the use of nets, the number of catches, etc., and any violation is poaching and will be severely punished. With these conservation measures, as well as the strong fecundity and adaptability of the Japanese eel, it is expected that their populations will gradually recover, as well as the northern bluefin tuna, which was also once listed as endangered.
04 Migratory fish in rivers and lakes
Not all freshwater migratory fish must enter the ocean during their lifetime, there are some migratory fish living in the Yangtze River, such as our common "four big fish": herring, grass carp, silver carp and bighead carp, as well as carnivorous fish, snakehead and shark, as well as huge white sturgeon, will migrate to rivers and lakes, these fish will enter the deep water lake of Tongjiang River in autumn and winter to fatten and winter; In spring and summer, especially during the flood season, it enters the main river to breed and spawn. For example, the Yangtze sturgeon and white sturgeon will spawn and breed in the waters of the Jinsha River in the upper reaches of the Yangtze River, while the juveniles of the white sturgeon will swim downstream to the Yangtze River estuary to feed and fatten for winter. Fish, snakehead and shark will lay floating eggs in the upper reaches of the Yangtze River, and the eggs will gradually develop and hatch in the process of drifting. Fourth, the big fish will also spawn in the upper reaches of the Yangtze River or tributaries of the Tongjiang River during the breeding season.
Photo 6: White sturgeon (courtesy of Shen Yuxi)
Figure 7: Juvenile Chinese sturgeon (Source: Wikipedia)
However, the interception of these fish migration routes by water conservancy facilities and the resulting changes in hydrological conditions, as well as overfishing, especially illegal fishing methods such as ecstasy, extinction nets, ground cages, rolling hooks, electric fish, and fish explosions in rivers and lakes and tributaries, will have a very serious negative impact on the normal reproductive cycle of these fish.
With the implementation of the fishing ban policy, the population of the four large fish, which produce floating eggs, has rebounded, and the snakehead that has disappeared for many years has reappeared in the waters of Hubei, Jiangxi and other places. In July 2021, the Hubei Provincial Institute of Fishery Sciences conducted a field survey of fish resources in key waters of the Yangtze River along Dongting Lake, and found 2 mandarin carp in the "South Dongting Lake Grass Turtle Chinese Turtle National Aquatic Germplasm Resources Conservation Area", and it has been 20 years since the last time the mandarin fish was found in Dongting Lake.
The freshwater ecosystem of the Yangtze River, once riddled with overexploitation, has begun to burst back with vitality thanks to the implementation of conservation measures.
Author: Hu Kai Science Popularization Research Tutor, Scientific Consultant of CCTV-9 Documentary Channel
Review: Yu Fandong, member of the science popularization expert team of the Chinese Fisheries Society, and doctor of the Pearl River Fisheries Research Institute of the Chinese Academy of Fishery Sciences
Producer: Popular Science China
Producer: China Science and Technology Press Co., Ltd., Zhongke Digital Innovation (Beijing) Digital Media Co., Ltd