Many of the real-life Nemos swimming in children's fish tanks were caught using cyanide, according to research published Thursday which flagged the toxic threat to already-stressed corals, the creatures' natural home.

Friday's release of Pixar's "Finding Dory", an animated film about a forgetful blue tang, will likely boost demand for aquarium specimens of the tropical fish, and fuel the poisonous practice used to trap them, a report said.

The movie's prequel, "Finding Nemo", saw more than a million clownfish harvested from tropical reefs, said Craig Downs of the Haereticus Environmental Laboratory in Virginia, a research body which worked on the report with conservation group For the Fishes.

One of the most common, though illegal, ways of capturing the agile swimmers is with cyanide.

"For them to be caught... you squirt cyanide onto a fish or it goes into this cloud of cyanide and it is stunned," Downs said.

The team reported that more than half of the saltwater aquarium fish they bought from US pet stores and wholesalers tested positive for cyanide residue.

They had tested over 100 fish, including blue tangs.

The results would likely be similar in other countries, given that most of the world's aquarium fish come from the same suppliers, Downs told AFP.

Tests on European pet fish will follow next year.

- Huge trade -

What is the lure for poisoners? An ornamental reef fish trade valued at over $1 billion, according to the website of environmental group WWF.

An estimated 300,000 blue tangs alone are traded every year, then sold for as much as 150 euros ($170) apiece.

"The 'Dories', the blue tangs, the ones I purchased, all had, except for one, very high levels" of cyanide residue," said Downs, and "did not survive beyond nine days after purchase".

But worse than customer deception, the practice of cyanide fishing devastates the exotic pets' natural habitat -- coral reefs already assailed by climate change, pollution and ocean acidification.

"A bleached coral has a high possibility of recovering if there's no other pollution stress around it," said Downs.

"But if you throw a cloud of cyanide over a reef to stun all the fish and that coral is bleaching, that reef is dead. It will kill all the coral."

The fish species themselves were not threatened with extinction, he said.

But he added: "In 50 years, there's going to be so few reefs... that most of the fish will probably be put on the endangered species list."

- Difficult to breed -

The species with the highest cyanide exposure was the iridescent Green Chromis -- the world's most traded aquarium fish, the report found.

The 2003 film "Finding Nemo" about a clownfish separated from its family, unleashed massive demand for real, live versions of the tropical beauty.

Wild clownfish populations plunged, prompting much reasearch into farming them instead.

The only way to tackle cyanide fishing, say researchers and commentators, is for consumers to buy cultivated fish instead of wild-caught ones.

"Today, we breed more and more sea fish, including two species that we could not get to reproduce (in captivity) only 10 years ago: the Angelfish and the Humpback grouper," said Pierre Gilles, a biologist at Monaco's Oceanographic Institute.

Blue tangs are difficult to breed in captivity, though this may change if demand skyrockets.

The United States, Europe, Japan and China are the world's top consumers of ornamental fish, said the report, with the Philippines and Indonesia the main suppliers.

The data will be presented to the International Coral Reef Symposium in Hawaii next week, and submitted to a scientific journal for publication later in the year.