Just as pregnant women are advised to avoid fish caught in the Baltic Sea and in freshwater lakes, a genetic variation in 20 percent of men also puts them at risk.

The study of 680 men from Sweden, Poland, Ukraine and Greenland found that among those who had a specific genetic variation and were subjected to high levels of toxic substances found in the fish, their sperm counts were 40 percent lower, The Local reported Saturday.

Swedish researchers at Malmo, Lund and Ahus University hospitals found that toxic substances in the fish, including PCB and dioxin, can adversely affect sperm production.

Lead researcher Yvonne Lundberg Giwercman said men who wish to become dads should avoid Baltic fish.

However, the National Food Administration has no plans to change its recommendations, an official said.

"The research is very important but before we change the food recommendations for Baltic Sea fish we would like to see similar results from other research groups," said administration official Anders Glynn.