Vaccinations could one day come in the form of a tasty morsel of fish, rather than via an injection, researchers have claimed.
The zebrafish could replace the syringe
Singaporean researchers have created zebrafish that produce vaccines in their muscles.
They say the technology could also be used in more commonly eaten fish, such as salmon.
But they say the fish would have to be eaten raw because cooking would destroy the vaccine.
Researchers from the National University of Singapore have genetically modified zebrafish so that they produce hepatitis B vaccine.
The next stage will be to test the sashimi vaccine on animals which can be infected with hepatitis B to see if eating the fish has a protective effect.
The researchers say previous studies in this area to make vaccines in plants or animals in this way have been unsuccessful because they do not produce enough protein.
But they suggest the zebrafish could produce large amounts of protein. They estimate every kilo of fish muscle could produce 27 grammes of vaccine.
They say edible vaccines could be fed to farm animals and fish in their feed.
Other scientists have already created sheep that produce human proteins in their milk and goats that can be milked for spider-web proteins.
Professor Gong Zhiyan, the biological scientist who is leading the research, is an expert on zebrafish, and has carried out a number of studies, including creating genetically modified fluorescent fish.
He told The Straits Times newspaper that using fish would be cheaper than other methods of producing vaccines.
He added there would be no concerns over passing on diseases to humans - as there would be if mammals such as cows were used.
However Professor Gong added: "We haven't reached the stage yet where we know how many fish you would have to eat for a correct dose of vaccine, but based on the high levels of the protein they produce, it shouldn't be much."
The researchers stress that edible vaccines are in the early stage of development and years of research will be required before they can be made widely available.
Professor Jim Johnson of the Department of Microbiology and Immunobiology at Queen's University, Belfast, told BBC News Online: "It's extremely unusual for vaccines to be delivered through the gut.
"But we use a sugar pill for polio, so it is possible."
Professor Johnson said the scientists would have to ensure the vaccine was able to survive the digestive process.
He added: "It would have to pass into the bloodstream in a form which could be recognised by white blood cells for using to develop immunity against a disease."