NEW YORK (Bloomberg) - Merrill Lynch & Co., the world's biggest brokerage firm, ousted the co-head of its Asian fixed-income business amid a management shake-up following $8.4 billion of losses on sub-prime mortgage-related securities and bad loans.

Ranodeb "Ronnie" Roy, who is based in Hong Kong, said in a phone interview that he was asked to leave the company in a meeting this morning.

Mr. Roy, 39, declined to give a reason for his departure. Antony Hung, who co-led Merrill's fixed income, commodities and currencies businesses in Asia along with Roy, will become the sole division chief, according to an internal memo sent to Merrill employees yesterday.

The firm fired its global head of fixed income, Osman Semerci, and Dale Lattanzio, co-head of the division's Americas operations, last month, before announcing the writedown of its sub-prime assets.

David Sobotka, head of the firm's commodities unit, replaced Semerci as fixed-income chief.

Stan O'Neal, Merrill's former chief executive officer, was forced to resign on October 30 after reporting the biggest quarterly loss in the New York-based firm's 93-year history.

Former Goldman Sachs Group Inc. President John Thain, who has run the New York Stock Exchange since 2004, was hired as Merrill's new CEO last week.

Thain, who's slated to replace O'Neal on December 1, said he plans to bolster the upper ranks of Merrill's trading division.

"On the sales and trading side, we probably are going to add some senior management," Mr. Thain said in a November 15 interview. "There is plenty of talent on Wall Street right now and I'm already getting plenty of resumes."

Merrill fell 21 cents to $53.66 in NYSE composite trading. The shares have dropped about 42 percent this year, the most among the five biggest US securities firms.

Jessica Oppenheim, a spokeswoman for the firm, confirmed the memo announcing Mr. Hung's appointment as Asia fixed-income chief. She declined to comment on Mr. Roy's departure.

Roy joined Merrill Lynch in 1999 from Barclay's Capital as head of credit trading in Asia.

In 2006, he was promoted to oversee exotic credit products, and was named co-head of fixed income in Asia earlier this year.

Mr. Hung, 48, joined Merrill in 1993.