Introducing fish of any type into the diet curbed the risk of contracting the skin condition by 25 percent compared with children who never ate it, Bernt Alm, a paediatrician at the University of Gothenburg in Sweden, and colleagues reported in the British Medical Journal.
"The main finding was that early introduction of fish was beneficial," Alm said in a telephone interview. "There was no link with the amount of fish or type of fish. We think it is more the timing of the introduction."
Eczema is a chronic condition affecting between 10 and 15 percent of children that can cause the skin to become itchy, red, dry and cracked. It often affects those prone to allergies.
The Swedish study is part of research tracking the long-term health of nearly 17 000 babies.
The researchers found that genes played an important role in the development of eczema but breast-feeding and keeping a furry pet in the house had no effect.
Fish in the diet appeared to be important, but Alm said it would take further investigation to establish why. There was no extra protection from fish rich in omega-3 fatty acids, which provided other health benefits, Alm said.
"It must have something to do with its influence on the developing immune system," he added.