Illegally introduced into China as aquarium fish decades ago, the alligator gar poses a severe threat to the country's ecosystems due to a lack of natural predators, experts said.

Gu Dang'en, a scientist with a national program on alien invasive species control, said the fish was brought into China two to three decades ago for its strange spotted look.

At the beginning, the fish were smuggled into the country, he said. Since the turn of the millennium, however, they have been available via breeding.

"It's quite possible that the 'monster' fish in Ruzhou was bought for breeding and then released into the lake," he was quoted as saying by several media outlets, including the China News Service.

An alligator gar was spotted in a lake in Ruzhou in mid-July, followed by an operation to catch it.

After it became an online sensation, some online platforms pulled the fish off their shelves but it is still available elsewhere at prices ranging from dozens of yuan to several hundred, depending on size.

As a predator at the top of its food chain, alligator gar can eat as much as 5 percent of its own body weight in a day, China Central Television quoted an unnamed aquarium employee in Pingdingshan, Henan province, as saying.

Fish, crustaceans, amphibians, reptiles and birds, as well as small mammals are its food. It is extremely destructive to the ecosystem, the employee added.

Mu Xidong, a researcher with the Pearl River Fisheries Research Institute at the Chinese Academy of Fishery Sciences, said the Biosecurity Law, which was approved by national legislators in October 2020 and took effect in April last year, stipulates that the government should draft a list of alien invasive species and work out regulations for their management.

Authorities have unveiled a national plan to conduct surveys of 10 invasive species, among them the alligator gar, he said.

Ren Dapeng, a professor from the China Agricultural University, said under the Biosecurity Law, institutions and individuals cannot import, release or discard alien species without official approval and both institutions and individuals face fines of between 10,000 yuan ($1,455) and 50,000 yuan for doing so.

He said that if people no longer want to raise alien species like the alligator gar, they should send them to authorities for safe disposal.