World Fisheries Day丨There are many farmed fish, so why are some wild fish still so "crispy"?

Today is World Fisheries Day. Fish are the most diverse and largest group of vertebrates on Earth. According to Fishbase, a world fish database, there are about 34,300 known fish species, which inhabit rivers, lakes and seas. Fish are useful to humans in many ways, but the biggest use is probably for eating.

However, long-term overfishing of fishery resources has put many fish species in danger: the populations of round-mouthed copper fish, curly-mouthed fish, Guihua dace, long-nosed catfish, etc. are heading for depletion; white sturgeon, bighead carp, Xichang whitefish, shad, large-scale silver carp, etc. are endangered, critically endangered, or even extinct. In the face of problems such as "difficulty in eating fish", we vigorously develop artificial breeding to ensure the supply of fish while avoiding excessive consumption of some wild fish populations.

White sturgeon (Photo provided by Shen Yuxi)

The word "crispy" has been very popular on the Internet recently, describing a person or thing that is fragile and easily damaged. Since we have mature fish farming technology, rich farming species, a large farming scale and a large amount of resources, why are wild fish still so "crispy"? Why can't we "feed back" to wild populations through farmed fish?

1. Restoring the wild population of fish does not mean releasing the fish raised in fish ponds, reservoirs and factories directly into rivers, lakes and seas.

1. Some farmed fish have undergone multiple generations of hybridization and selection. If they are released into the wild rashly, they may hybridize with wild original species and pollute the gene pool of wild fish.

For example, the Tianjin Golden Carp was obtained by distant hybridization with scattered-scale mirror carp as the female parent and red carp as the male parent.

Tianjin Golden Carp (Photo provided by Shen Yuxi)

2. Farmed fish are often raised in water at high densities, and are likely to carry a variety of pathogens, which can be transmitted to wild fish after being released.

Fish have very different body structures and kinship from humans, so there are very few diseases that are common to humans and fish. Farmed fish on the market are also subject to strict food quarantine and residual drug inspections, so humans can buy farmed fish on the market with confidence. However, if they are released without quarantine, the pathogens they carry may spread to the wild environment, posing a threat to wild fish. For example, koi and carp carrying koi herpes virus may transmit the virus to wild carp and crucian carp.

3. Some common edible fish that are widely farmed are alien species. Once released into the wild, they may cause harm to native species in local water bodies, bring about serious biological invasion problems, and even trigger ecological disasters.

For example, the Nile tilapia, largemouth bass (California bass), rainbow trout, freshwater grouper, catfish (Qingjiang fish) in freshwater, and the American redfish and turbot (turbot) in the ocean are all "coveted" but actually "alien species" stars. Once released into natural waters at will, they may become invasive species.

Largemouth bass (Photo provided by Shen Yuxi)

Therefore, indiscriminately releasing farmed fish will not only fail to restore fishery resources in natural waters, but may also destroy wild fish populations and the ecological balance of water bodies .

When releasing any artificially bred fish into natural waters in the wild, it is necessary to strictly control their germplasm resources and quarantine, and they must be released scientifically under the guidance of professionals from relevant departments . Many common farmed species cannot be used for release and reproduction.

Second, even for some native fish that can be farmed, current artificial breeding technology is not mature enough to “meet the market and save wild populations.”

1. The yellow croaker is often "taken for its swim bladder"

The yellow croaker is a second-class protected animal in my country. The fish maw made from its maw is called "golden money fish". Due to its high price in the market, the yellow croaker has been overfished for many years and has become a critically endangered species, with its wild population almost extinct.

Yellow croaker larvae (Source: video screenshot)

Adult yellow croaker (Source: video screenshot)

At present, Huizhou and Dongguan in Guangdong have made breakthroughs in the artificial breeding technology of yellow croaker, and can save the wild yellow croaker population on the brink of extinction by breeding and releasing fry. However, the use of artificially bred yellow croaker is still limited to scientific research, conservation, etc., and there is still a long way to go before it can escape the endangered situation.

2. The two treasures of the Yangtze River: Acipenser sinensis and Acipenser dabryanus

There has been no record of natural reproduction of these two species of fish for many years, and the Dabryan sturgeon was declared extinct in the wild by the IUCN Red List last year.

Since the 1980s, the Chinese Sturgeon Park in Yichang, Hubei Province has been releasing artificially bred Chinese sturgeons and Acipenser dabryanus into the wild. Thanks to the efforts of scientific researchers, artificially bred Acipenser dabryanus has also successfully spawned and reproduced in artificial ovaries in the wild environment.

However, it is not yet enough to remove these two species from the critically endangered list, and it is too early to restore the historical population numbers.

Acipenser dabryanus (Source: Wikipedia)

Juvenile Chinese sturgeon (Source: Tuchong Creative)

The adaptability problems of artificial populations and the destruction of habitats have made it difficult for some populations that have successfully reproduced under artificial conditions to survive and continue in the wild.

3. The breeding technology of some farmed fish is not mature and cannot escape the plunder of wild resources.

1. Japanese eel: The extremely difficult process of giving birth

The main ingredients of the delicious dishes such as "Kabayaki" and "Eel Rice" in Japanese restaurants are Japanese eels.

Japanese eel (Source: Wikipedia)

Adult Japanese eels live in fresh water, but they must migrate to the sea to reproduce - they enter the ocean from the mouth of rivers, swim all the way to the deep sea near the Mariana Trench in the Philippines to spawn and reproduce, and then die. Newborn eels (commonly known as "willow leaf eels") live in the deep sea for a period of time, undergo metamorphosis, and then swim upstream from the estuary into fresh water to grow and fatten.

The growth and development process of Japanese eel (Source: Wikipedia)

This special breeding habit, coupled with the willow eel's stringent requirements for living environment and food, means that we are currently unable to breed Japanese eels in large numbers under artificial conditions.

Some of the Japanese eels currently sold on the market are caught directly from the wild, while most are eel fry caught from estuaries and raised and fattened in artificial environments. Due to overfishing, the Japanese eel, which once had a huge population and strong reproductive capacity, has now become an endangered species.

IV. Summary

Commercial artificial breeding alone cannot save wild fish populations. In order to protect these water elves on the verge of extinction and to maintain species diversity and ecological balance, China has formulated many policies to protect rare and endangered aquatic wildlife and fishery resources, such as listing some wild fish populations as first- and second-class protected animals and imposing strict quota restrictions on the fishing of some fish .

For the general public , ordinary consumers should try to choose aquatic products that are easy to breed artificially and have mature breeding technology, such as salmon, and try to consume less or no species that are difficult to breed artificially and have poor wild population conditions, such as large sharks , large rays , wild yellow croaker, etc.

Only in this way can we effectively protect the ecological environment of water bodies, restore fishery habitats, and recover wild fishery resources, so that we and our future generations can continue to enjoy the rich gifts of nature's rivers, lakes, and seas.

Author: Hu Kai, science research instructor, CCTV-9 documentary channel science consultant

Reviewer: Gu Dangen, Associate Researcher, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.