In middle July 2022, “strange fish” appeared in Yunchan Lake, Central Park of Ruzhou City, He’nan, China, which caused the local government to attach great importance to it. The park management timely organized forces to stage a real action of "fishing by draining the lake water". 300 000 cubic meters of lake water was drained to catch the "strange fish" to prevent the invasion of alien species. Identified by experts, "strange fish" in the lake were actually the alien species alligator gars (Atractosteus spatula) that have frequently appeared in China in recent years.

According to the introduction of management personnel from Ruzhou Central Park, the management began to check the five lakes in the park by pumping water on July 26. On the early morning of August 27, the location of the alligator gars was locked, and the local staff started to "catch" the strange fish. During the siege, the rescue teams from many places took joint action and dispatched two underwater robots to probe the pipeline.

After more than 40 days of search and nearly 30 days of draining the 300 000 cubic meters of water in Yunchan Lake, finally, two alligator gars in the waters of Yunchan Lake were captured and confirmed to be one female and one male, with the body length of about 70 cm and 90 cm (Figure 1).

Why did Ruzhou of He’nan spend one month to drain 300 000 cubic meters of lake water and use the method of "draining the lake water" to subdue the alligator gars? It is understood that the alligator gars are carnivorous fish with fierce nature. As a prehistoric fish that has lived on the earth for more than 100 million years, the alligator gars are not "good species". They will "wipe out" the native aquatic organisms in China, especially the fish in the water. The algae, food of fish, will flood in large areas, and these aquatic plants will form the advantage of a single species in the water area, which is very likely to cause hypoxia in the water and cause ecological disasters. At the same time, the alligator gars are high-risk alien species and lack natural enemies. In case of food shortage, they may even attack humans and cause personal injury.

Behind the "circusee" of the alligator gar incident in Ruzhou, He’nan Province, China, in fact, it highlights the ecological crisis caused by the invasion of alien species in China in recent years. More than ten years ago, the alligator gar was discovered in the wild waters of the Pearl River Delta in Guangdong, and has taken root in the Pearl River. Alligator gars are not only frequently found in the waters of the Pearl River Delta and in the cities and counties in the mountainous areas of Guangdong, but also there have been records of wild alligator gars in Guangxi, Fujian, He’nan, Sichuan, Jiangsu and other provinces in China, which is seriously threatening the ecological environment. It is precisely for this reason that the news of "strange fish" in He’nan, China, has attracted much attention. The local management personnel even took great pains to catch them and did not hesitate to drain the lake.

News background: About alligator gar (Atractosteus spatula)

The alligator gar, also known as the Fu’e in Chinese, belongs to the Antipodocottus genus in the family of Lepisosteidae in Lepisosteiformes. The body length is generally 1.2~1.8 m, and weight at 45~72 kg, which is the largest of the seven existing species of Monopterus (Figure 2). The alligator gar is named after its long and cylindrical body, protruding snout, short snout and two rows of sharp teeth on its upper and lower jaws like those of a crocodile. It is mainly distributed along the Gulf of Mexico from Mexico to the United States, Missouri River and Ohio River, Nicaragua and other places.

Figure 2 Alligator gar (from Wikipedia)

The alligator gars were introduced to China as ornamental fish, which have achieved native reproduction in Guangdong. They are alien species frequently found in China in recent years. As the alligator gars are carnivorous fish, there are no natural enemies in Chinese waters. “As long as there are living creatures in the water, almost all of them will be eaten by alligator gars”. Alligator gars are extremely destructive. If they are released into natural waters, they will bring disaster to the local water ecosystem.

Not only that, its eggs are highly toxic. Alligator gar is not literally “Fu’e (means lucky alligator)” in Chinese. Alligator gars mate and lay eggs from May to August every year. The female fish lays 140 000 to 200 000 highly toxic eggs each time. The eggs are light green and mostly adhere to aquatic weeds or gravels, and the incubation period is about 6 to 8 days. The male fish can reach sexual maturity at the age of 6, with an average life span of 26~50 years and the highest record of 75 years.

Such a long life, coupled with the highly toxic nature of eggs, the alligator gars quickly achieve population superiority in the absence of natural enemies. Moreover, alligator gars have no chewing ability so they eat only by swallowing. They can swallow up the food as big as 1/4 of its body volume. Its ferocity can be seen from its solution to the problem of "Asian carp" which has been flooding in the United States for 30 to 40 years. This also gets the alligator gars out of the dilemma, which had been greatly reduced in number before because they attacked anglers.