Scientists are hoping to discover exactly how oily fish can protect against Alzheimer's disease.
Eating oily fish 'won't harm anybody', the researchers say
It is known that eating fish such as salmon, sardines and mackerel appears to cut the risk of developing dementia.
But now, Cardiff University researchers funded by £300,000 from the Alzheimer's Research Trust are to investigate how this might help.
In the meantime, the researchers say people should eat oily fish at least twice a week.
The three-year study will be carried out on mice which have been genetically designed to have an Alzheimer's-like disease.
Researchers will monitor the effects of different diets on the mice.
Preliminary research has shown that feeding the mice oily fish improved their brain function.
'Easy thing to do'
Professor John Harwood, who is leading the research, said: "We put the mice through a maze, and the ones with normal brain functions learn quickly when to turn left and right, but the Alzheimer's mice are absolutely hopeless at remembering.
"When we put them on a diet rich in these fatty oils, their ability to learn improved greatly."
It is suggested that the omega 3 oils contained in the fish could prevent the build-up of a protein called amyloid, which grows like a plaque on the brain of Alzheimer's sufferers, and slows down brain functions.
Professor Harwood added: "There have already been a number of studies showing that people who consume a significant amount of oily fish or fish oil capsules seem to have a smaller incidence of Alzheimer's disease.
"A study in Chicago last year showed people who included oily fish in their diet had 60% less chance of developing Alzheimer's.
"Including oily fish in the diet is a very easy thing that anybody can do, without going to a hospital.
"It won't cure Alzheimer's but the evidence is it will slow the rate of deterioration, and it should stop you getting the disease if you don't already have it."
He added: "Eventually, it's possible people will be advised to take fish oil capsules.
"It's difficult to know the exact amount of omega 3 you are getting in your diet, where you would know how much you were getting if you took capsules
Harriet Millward, of the Alzheimer's Research Trust, said "We are funding 25 research projects in all, but the oily fish study looks very promising.
"We hope the research into the biology of Alzheimer's disease will give us a greater understanding of how the disease develops and lead to other new treatments."
The trust is also funding research into how B vitamins produced by the body contribute to the development of Alzheimer's, and a second on the use of computer-aided drug design.