But the RSPCA has called on the device to be banned because it is too small to provide fish with adequate oxygen supplies and a clean environment. The iPond is sold nationally by the Pets Paradise and Pet Goods Direct chains. Users can play their iPods through a speaker built into the bottom of the brick-shaped tank.

The tank's water capacity is about 650millilitres once rocks are placed in it. Pets Paradise is selling Siamese fighting fish with the iPond. The fighting fish are native to South-East Asia and have a "labyrinth lung" that allows them to take in oxygen from air. Typically they live in puddles and rice paddies.

A Melbourne Aquarium spokesman said Siamese fighting fish required a minimum tank size of 10 litres - dramatically more than the iPond provides. Animal Liberation Victoria's Noah Mark said he was disgusted by the invention.

Studies proved fish had memories well beyond a few seconds and were social creatures that experienced pain and boredom, he said. "The fish in this thing does not look like it has very long to live and it can barely move," he said. "Even if it does live it's not [a] life worth living ... it's really just a torture box."

Acoustics expert Jason Gedamke said there was no doubt noise from the speaker would escape into the water. "The speaker is directly coupled to the outside of the tank ... [so] you are going to have a small level of sound introduced," Mr Gedamke said.

"It's the same as putting a fish tank on a speaker." RSPCA spokesman Hugh Wirth said despite the fighting fish's ability to breathe air from the surface, the tank was far too small for it to receive adequate oxygen. The small volume of water would lead to rapid temperature change and this meant the tropical fish would not live long, he said. The iPond should be banned, Dr Wirth said. Marketing manager for the Pets Paradise and Pet Goods Direct chains, Alyse-Grace Robertson, said the tanks had gone on sale in September and were selling briskly.

The group that manages the stores had received one formal complaint about the product. Customers sometimes asked questions about the welfare of fish in iPonds.

"A few people ask, 'is the fish OK?"' Ms Robertson said. The chains were satisfied that fish in iPonds did not suffer. She said before selling the tanks the chains had consulted the Pet Industry Association of Australia. Output from the speakers was small and fish in iPonds seemed to flourish, she said.

A spokesperson for Apple said the company was willing to comment on its own products, but not on accessories made by third parties.