Your mother was right: Eating fish makes you smarter, according to a Swedish study released showing that eating enough of the aquatic vertebrates clearly heightens teenage boys' IQ levels.

We discovered a clear connection between frequently eating fish and higher (teenage IQ) scores," professor Kjell Toren, who headed up the study at the Sahlgrenska University Hospital in Gothenburg, said in a statement.

The study, published in the March issue of child health journal Acta Paediatrica, examined the general IQ scores, verbal abilities and spatial understanding of 3,972 Swedish boys in 2000 when they were 15 years old and again when they were conscripted in the military three years later.

Notable rise in IQ scores Boys who at the age of 15 ate fish at least once a week on average scored seven percent better on the general IQ test three years later, while those who ate fish more than once a week scored 12 percent higher, the study showed.

"There was a clear connection between regular consumption of fish at the age of 15 and improved cognitive abilities at the age of 18," Maria Aaberg, who co-authored the report, said in the statement.When it came to verbal abilities, 15-year-olds who ate fish once a week scored four percent better than their peers in tests three years later, while those who ate fish more than once a week did nine percent better.

Omega-3 essential-As for spatial understanding, 15-year-old fish eaters did seven and 11 percent better respectively in tests at the age of 18. Fish is a direct source of omega-3 fatty acids, which have been shown to be essential for cognitive development and normal brain functioning, and a number of international studies have shown that eating fish during pregnancy improves foetal intellectual development.

Other studies have revealed that fish consumption can help slow cognitive decline in elderly people. "It now appears that fish in the diet in a valuable way contributes to improving mental achievements in male teenagers," Aaberg said, pointing out that the Swedish study had taken into account a number of variables, including ethnicity, exercise and the education levels of the boys' parents.