Citigroup, the world’s biggest bank, said three of its top fixed-income traders are leaving to start a new venture.

Brian Riano, head of global credit trading, John Eckerson, and Sean Fahey will “pursue other endeavors,” a Citigroup spokeswoman, Danielle Romero-Apsilos, said yesterday, declining to elaborate. Mr. Eckerson was head of high yield trading and Mr. Fahey was an emerging-markets debt trader. All three were managing directors.

The departures may weaken a department that has helped fuel gains at Citigroup’s corporate and investment bank. Revenue from fixed-income sales and trading, a business built on the former Salomon Brothers, rose 16% in the first quarter to $2.92 billion, the highest in at least five quarters, Citigroup said last month.

“At a time when there’s stress in the credit markets, with losses on collateralized debt obligations and credit default swaps, you wonder whether organizations aren’t coming down on their credit people,” said Richard Bove, an analyst at Punk Ziegel & Company in Pinellas Park, Fla.

Citigroup’s head of European credit trading in London, James Higgins, and the head of investment-grade bond trading in New York, David Pichler, will replace Mr. Riano, Ms. Romero-Apsilos said. Both are managing directors.

Mr. Eckerson declined to comment and referred questions to Citigroup’s public-relations department. Messrs. Riano and Fahey didn’t return telephone calls seeking comment. Messrs. Higgins and Pichler also didn’t return calls and e-mail messages.

Corporate bond markets have slumped since Standard & Poor’s cut its credit ratings on General Motors and Ford Motor to junk status on May 5. Last week, stocks fell in part on concern that the downgrade was causing losses at hedge funds on collateralized debt obligations, which are pools of assets such as loans or bonds that are bundled together and sold to investors.

Mr. Bove said the departures may not weigh on Citigroup too heavily, as the bank employs more than 250,000 people. In November, Citigroup lost eight credit-derivatives traders, including 11-year veteran Doug Warren, to Barclays Capital.

The global credit-derivatives market more than doubled last year to $8.42 trillion, according to the International Swaps and Derivatives Association. Credit default swaps, contracts used to ensure against bad debts, are the fastest-growing part of the $220 trillion derivatives market.

Competitors also have lost credit traders in recent months. Jeremy Barnum, a former head of JPMorgan Chase & Company’s North American credit-trading unit, is now at Blue-Mountain Capital Management, a hedge fund. Geoff Sherry, another former co-head of JPMorgan’s credit-trading business, joined Caxton Associates LLC earlier this year. BlueMountain and Caxton are hedge funds.

Citigroup’s growth in fixed-income trading dates back to Travelers Group’s 1997 purchase of Salomon Incorporated for $9.3 billion. The former Salomon Brothers made the biggest bond-trading bets of any Wall Street firm in the 1980s under then-CEO John Gutfreund.

By 1992, Salomon had leveraged its $3.9 billion in shareholders equity more than 40-fold into almost $160 billion in assets. Citigroup’s $1.49 trillion of assets as of March 31 were less than 14 times its book value.

Travelers, led by Sanford Weill, merged Salomon with its Smith Barney brokerage to create the second-largest securities firm. Then Travelers merged with Citicorp the next year to form Citigroup.

Fixed-income sales and trading made up 48% of first-quarter revenue at Citigroup’s corporate and investment bank.

“The first quarter was probably the best quarter in the history of Citigroup in terms of profits in trading,” said Mr. Bove, who rates Citigroup a buy. “The second quarter is going to be substantially below that.”

Citigroup is under investigation by European regulators for a series of trades last August that roiled the continent’s government bond markets. The bank apologized for the transactions and placed the six traders involved under administrative leave pending the outcome of the probes.

Shares of New York-based Citigroup rose 89 cents to $46.80 in composite trading on the New York Stock Exchange.