[Smart Farmers] Don’t worry, foodies! This “exotic fish” can survive in saline-alkali land

Editor’s Note:

Protecting biodiversity and ensuring ecological security have attracted much attention from the international community today, among which the issue of alien species invasion is one of the hot spots. Internationally, alien invasive species are listed as the second most important factor leading to biodiversity loss after habitat destruction. The report of the 20th National Congress of the Communist Party of China emphasized "implementing major biodiversity protection projects... and preventing and controlling alien species invasion". The Central Document No. 1 of 2023 proposed to "severely crack down on the illegal introduction of alien species, implement major invasive species prevention and control actions, and strengthen the standardized management of "exotic pet" trading and release." The prevention and control of alien species invasion is related to food security, biological security and ecological security. In recent years, with the increasing frequency of commodity trade and personnel exchanges, alien invasive species have spread faster and the invasion pathways have become more diverse. my country has a vast territory, both land and sea, and complex and diverse landforms and climate, so most invasive species can find a suitable living environment in my country. Once harmful alien organisms enter and colonize (a state of long-term survival), it is very difficult to completely eradicate them, which will seriously affect the ecological environment of the invaded area and damage the sustainable development of agriculture, forestry, animal husbandry and fishery and the stability of the ecosystem.

What are the common alien aquatic species around us? What harm will these alien aquatic species bring? How should we prevent the invasion of alien species? Science Popularization China Smart Farmers has launched a series of popular science articles on "Preventing and Controlling the Invasion of Aquatic Alien Species". Welcome to follow.

Our protagonist today is the familiar exotic fish - tilapia.

Mozambique Tilapia Oreochromis mossambicus | Greg Hume

What kind of fish is tilapia?

Tilapia, which is mainly native to Africa, is called "African crucian carp" because it is similar to crucian carp. Although tilapia is similar in size to crucian carp and is an omnivorous fish like crucian carp, they are not crucian carp. Because tilapia belongs to the Perciformes, Cichlidae, while crucian carp belongs to the Cypriniformes, Cyprinidae, the relationship between tilapia and crucian carp is like the relationship between pigs (Mammalia, Cetiformes, Suidae) and dogs (Mammalia, Carnivora, Canidae), so African crucian carp (tilapia) is not crucian carp. In addition to this common name, it has other names, such as tilapia, South Sea crucian carp, Vietnamese fish, etc. It is called tilapia because tilapia was first introduced to Taiwan Province of my country by Wu Genhui and Guo Qizhang in 1946. Later, mainland my country successively introduced tilapia from Vietnam, Thailand and other Southeast Asian countries, and it is also called "Vietnamese fish" and "South Sea crucian carp". The introduced tilapia, after artificial hybridization, has the advantages of fewer diseases, fast growth, high yield and fewer bones, so it is welcomed by breeders and consumers and is called "longevity fish".

Coptodon zillii | uncontacted tribe

Oreochromis aureus

Why has tilapia become the main species in my country's freshwater aquaculture?

Tilapia is rich in nutrition, rich in high-quality protein, unsaturated fatty acids and various trace elements required by the human body, and is an ideal food for humans. Tilapia has strong adaptability. Although they are freshwater fish, they can survive in low-salt waters, so they can be cultivated in saline-alkali land comprehensive breeding, turning "agricultural deserts" into "land of fish and rice". Moreover, tilapia can adapt to low-oxygen environments and are suitable for large-scale breeding. At the same time, they have strong disease resistance. Under artificial breeding, they rarely get sick. They are not picky about food, have low breeding costs, grow fast with greed, and have no intermuscular spines, which are easy to eat. These characteristics make them very popular economic fish and are introduced all over the world. In addition, some tilapia also have high ornamental value and are widely loved by ornamental fish enthusiasts.

After tilapia was introduced into my country as an edible fish, it gradually became the largest foreign fish farmed in my country. According to production, it ranks sixth among freshwater farmed fish and first among foreign freshwater farmed fish, after silver carp, bighead carp, carp, crucian carp and grass carp. From 1990 to date, my country has been the country with the largest tilapia farming output in the world. In recent years, the output has remained above 1.6 million tons per year. It occupies a pivotal position in the international aquatic product trade, driving the development of a large number of related industries and enriching the practitioners.

Nile tilapia Oreochromis niloticus | ihunta

Why is tilapia included in the “List of Key Alien Invasive Species”?

Tilapia likes to fight, has a strong sense of territory and the habit of protecting its young. Even female tilapia of the genus Oreochromis will hold the eggs in their mouths to hatch, so the survival rate of tilapia fry is very high. Moreover, tilapia reproduces very quickly and can lay eggs many times a year. Fertilized eggs can hatch after more than ten days. Under suitable conditions, the young fish can reach sexual maturity after one quarter of growth. In addition, they have a omnivorous diet, are indiscriminate, and have a strong ability to adapt to the environment. If they escape or are illegally released into natural waters, they will quickly become a disaster, occupying the ecological niche of native fish and causing a sharp decrease in the biodiversity of rivers and lakes. Therefore, tilapia is showing a trend of flooding in many countries. In 2000, the Mozambique tilapia, Oreochromis mossambicus, was listed as one of the world's 100 most threatening alien invasive species by the World Conservation Union (IUCN); the Nile tilapia, Oreochromis niloticus, was included in the "China's List of Alien Invasive Species (Third Batch)" by the Ministry of Environmental Protection and the Chinese Academy of Sciences in August 2014; the Coptodon zillii was included in my country's "List of Key Managed Alien Invasive Species" by the Ministry of Agriculture and Rural Affairs and other departments in December 2022, and is one of the 59 key managed alien invasive species.

Ministry of Environmental Protection and Chinese Academy of Sciences: List of Invasive Alien Species in China (Third Batch)

Six departments released the "List of Key Alien Invasive Species under Management"

What do you think of alien species like tilapia?

How to view alien organisms is a scientific issue. We don’t have to be afraid of the word “foreign”, nor can we deny the positive role of alien organisms by generalizing.

Tilapia, a delicacy that often appears on people's tables, is a popular aquaculture product that plays an important role in enriching people's food baskets, filling fishermen's pockets, and promoting the development of the fishery industry. At the same time, if tilapia is not strictly managed during the breeding process, it may become an invasive species if it enters natural waters. After flooding, it will lead to the degradation of the aquatic ecosystem and function, threatening ecological security and making people disgusted. Therefore, we need to treat alien species such as tilapia scientifically and fairly, and pay attention to seeking benefits and avoiding harm while developing and utilizing them. Here we remind everyone not to discard alien species such as tilapia in natural rivers and lakes at will, so as to avoid destructive effects on the aquatic ecology.

Produced by: Popular Science in China to Benefit Farmers

Author: Zou Qiangjun, Associate Research Librarian of Science Communication at Beijing Aquatic Wildlife Rescue Center, Chief Expert of the Expert Team of Science Communication for Endangered Aquatic Animal Rescue in North China of China Fisheries Society

Scientific review: Researcher Liu Yadan, former assistant secretary-general of the Chinese Society of Fisheries and the country's chief scientific communication expert

Coordinator: Wu Yuetong

Proofreader: Zhang Liuyan