A fish could be used to produce a treatment for people with haemophilia and gunshot wounds, scientists believe.
Scientists have used GM fish to produce a blood clotting agent
Researchers have already made a blood clotting agent, known as factor VII, from genetically modified tilapia, a freshwater fish farmed for food.
As well as being used to treat a rare form of haemophilia, factor VII can also be used to stem internal bleeding.
The research is being carried out by the University of Southampton and US experts, the New Scientist reports.
Factor VII is already produced using hamster cells but the cost of a single injection can be as high as £6,000.
It is used to treat a rare form of haemophilia, sometimes known as Alexander's disease, and for people with the more common haemophilia A and B who reject traditional forms of treatment.
But the protein has also been used by soldiers to stem bleeding caused by accidents and gunshot wounds.
Professor Norman Maclean of the University of Southampton, who led the research, told BBC News Online he was hoping to produce the protein for about a tenth of the current price.
The project, which is being run in conjunction with the Florida bio-tech firm AquaGene, has produced the protein by adding a human gene to the fish, which then excretes the factor VII into its blood.
The protein is then removed from the blood and transferred into humans.
He said: "It works by forming clots when someone has internal bleeding.
"The form of haemophilia it could treat is quite rare so I think the largest benefit will come from treating crash victims and people with gunshot wounds who have severe internal bleeding."
Prof Maclean said he also believed fish could be used to treat other diseases.
"There are a number of human therapeutic proteins that could be produced via fish to treat lung disease, liver problems, even tumours.
"The advantage with fish is that they are cheap and can be bred rapidly."
Prof Maclean said the fish-derived factor VII was still three years away from being on the market. The team still have to convince regulators that it is safe.
A spokesman for the Haemophilia Society said treatment at the moment was extremely costly and welcomed the prospect of cheaper alternatives.
"The form of haemophilia we are talking about is pretty rare, only one in a million people are affected. But the treatment does work."