Deutsche Bank AG was dethroned after a nine-year reign as the world's biggest currency trader by Citigroup Inc., a Euromoney Institutional Investor Plc survey showed, as subdued volatility depressed trading in the euro.

Citigroup, which last led the ranking in 2002, claimed 16.04 percent market share, beating Deutsche Bank's 15.67 percent, Euromoney said in a statement. The U.S. bank trailed its German rival by just 0.28 percentage point in the 2013 poll, the second-slimmest margin since it began in 1976. Barclays Plc was the third-largest trader, with a 10.91 percent share.

The biggest dealers in the $5.3 trillion-a-day foreign-exchange market are facing reduced revenues after stimulus efforts by central banks around the world muffled many of the trends that traders and investors use to make money. That's adding to competition among banks, which are pushing more trading onto electronic platforms to boost market share.