The transparent creatures are part of efforts to reduce the need for dissections, which have become increasingly controversial, particularly in schools.
‘You can see a live heart and other organs because the scales and skin have no pigments,’ said Yutaka Tamaru, an associate professor in the department of life science at Mie University.
‘You don’t have to cut it open. You can see a tiny brain above the goldfish’s black eyes.’
The joint team of researchers at Mie University and Nagoya University in central Japan produced the ‘ryukin’ goldfish by picking mutant hatchery goldfish with pale skin and breeding them together.
‘Having a pale colour is a disadvantage for goldfish in an aquarium but it’s good to see how organs sit in a body three-dimensionally,’ Tamaru said.
The fish are expected to live up to roughly 20 years. They could grow as long as 25cm (10in) and weigh more than 2kg (5lb), much bigger than other fish used in experiments, such as zebrafish and Japanese medaka, Tamaru said.
‘As this goldfish grows bigger, you can watch its whole life,’ he said.
Meanwhile another group of researchers, who announced in 2007 they had developed see-through frogs, said they planned to start selling the four-legged creatures, whose skin is transparent from the tadpole stage.