They would be more at home in the Indian Ocean - but for thousands of these Zebrafish, home is a series of bubbling tanks at the University of Bath near Bristol.

BBC Bristol's Mark Ashton reports

They are colourful creatures with black and white flashes down their backs - hence the name. But their delightful appearance is of passing interest only to the scientists. The fish show a similar genetic defect to that found in children who develop the painful bowel disorder called Hirchsprung's disease.

One in 5,000 children are born with it, and it requires immediate surgery. Dr Robert Kelsh, who is leading the Bath research team, believes Zebrafish are ideal animals for study.

Spots and stripes

He spends much of his time looking at a single mutant Zebrafish embryo under a powerful microscope. The defective genes that have caused some of their spots and stripes to mutate are very similar to the defective genes that trigger Hirchsprung's disease.

"Hirchsprung's disease can best be studied in an animal that mimics the disease," he says.

"In some of these Zebrafish we have embryonic fish that show the same sorts of defects as a Hirchsprung's disease patient might show - and by studying what goes wrong in the development of those fish, we hope to understand what wrong in a Hirchsprung's disease patient."

Devastating effects

One mother who knows more than most about the devastating effects of the disease is the writer and journalist Bel Mooney, who lives near Bath. Her daughter Kitty was born with Hirchsprung's disease and, because she has written about the disorder, she regularly gets mail from other worried parents. She is hopeful the fish may lead to an eventual cure, but she also recognises that current surgical techniques have made a tremendous difference.

"You have to have a lot of courage because the child will have to have a lot of operations," she says.

"It's extremely upsetting and disturbing to family life - just like any surgery, and it doesn't necessarily go away. Kitty had her first operation at two days old and her last operation last year, and she is now 18. I don't go in for glib messages of hope, but the condition can be stabilised with surgery."