By Alex Kirby
BBC News Online environment correspondent
Some of the most colourful and attractive fish to swim the tropical seas may be threatened by the aquarium trade, the United Nations believes.
Resplendent: Harlequin tuskfish (Image: Ove Hoegh Guldberg)
It says over 20 million fish and about half as many other forms of marine life are caught every year for the trade.
There is also a persistent demand for some forms of coral, the UN believes.
But it says the aquarium trade, if it is properly managed, can help coastal communities to climb out of poverty.
The report, From Ocean To Aquarium: The Global Trade In Marine Ornamentals, is launched by the UN Environment Programme's World Conservation Monitoring Centre (Unep-WCMC), which is based in Cambridge, UK.
The report is timed to coincide with the launch of the Disney movie Finding Nemo, the story of a clown anemonefish separated from his dad on Australia's Great Barrier Reef, who ends up in a dentist's surgery.
Together with the blue-green damselfish, the clown fish heads the list of the most traded tropical fish.
Philippines seahorse fisherman (Image: A Vincent)
The report says the annual catch from tropical seas for the marine aquarium trade in Europe and the US totals more than 20 million fish from 1,471 species, ranging from the sapphire devil to the copperhead butterflyfish.
Another 9-10 million creatures from about 500 species, including molluscs, shrimps and anemones, are caught as well, with up to 12 million stony corals taken from the wild each year.
Hope for the poor
The report says the annual value of the trade, which is concentrated in south-east Asia, is $2-300m. In the Maldives, one kilogramme of aquarium fish was valued at almost $500, while the same weight of reef fish for food was worth only $6.
The live coral trade is worth about $7,000 per tonne, against $60 for a tonne of coral used for making limestone.
Cardinal fish: Widely sought (Image: Colette Wabnitz)
The UN says the aquarium trade is worth about $5.6m a year to Sri Lanka, providing 50,000 people in low-income areas with jobs - and, it says, with a strong incentive to conserve the fish and the reefs.
The executive director of the UN Environment Programme, Dr Klaus Toepfer, said: "Collecting tropical fish brings pleasure to millions.
Barbaric and short-sighted
"The global trade in marine species poses a significant risk to valuable ecosystems like coral reefs, but it has great potential as a source of desperately-needed income for local fishing communities."
Although the trade is mainly legitimate, the report details some methods which are certainly not sustainable.
Giant clams are not immune (Image: Cedric Genevois)
One of the authors, Colette Wabnitz, said: "A minority of fishermen, in countries such as Indonesia, use sodium cyanide to capture fish. An almost lethal dose of the poison is squirted into the reef where the fish shelter.
"It stuns them to allow capture and export, but can also kill coral and other species. The fish may survive the export process but usually die of liver failure soon after being purchased."
The report relies heavily on data from the Global Marine Aquarium Database, compiled by Unep-WCMC, the Marine Aquarium Council (MAC), and members of different trade associations.
Ed Green, another of the report's authors, urged traders to sign up to the MAC certification scheme.
He said fish certified by the council were healthier and had a better chance of survival because they were treated according to internationally approved standards of best practice.