That's the question facing investment bank chiefs as they try to squeeze costs and improve returns. Some are clinging to the hope that diving revenue from a "complex, messy business" will be temporary, and they need to keep trading teams together for when the market recovers.

However, many are already changing, and the likes of Deutsche Bank (>> Deutsche Bank AG), Barclays (>> Barclays PLC) and Morgan Stanley (>> Morgan Stanley) look set to make deeper cuts to their fixed income divisions to deal with weak volumes and tough regulation.

Investment banks are reshaping themselves to increase their profitability, and the trading desks that buy and sell interest rate and credit products are under most scrutiny.

Revenues from fixed income, currencies and commodities (FICC), particularly in interest rates, suffered badly last year as the tighter regulations imposed following the financial crisis started to hurt. Switzerland's largest bank, UBS (>> UBS AG), is largely pulling out of fixed income and the pressure on its peers could get worse.

"The problem in fixed income is being sold by investment banks as cyclical, but it's a structural one," said Chirantan Barua, analyst at Sanford Bernstein. "Everyone is just solving around the edges, no-one other than UBS has taken a sword to the balance sheet, just in case the market turns and they don't want to be caught without capacity."

FICC trading accounts for about half of investment banks' income but the sums are falling. Across the top 11 banks which have reported their 2013 results so far, it fell 10 percent from 2012 to $83 billion (49 billion pounds) last year, according to analysis by Reuters.

Most alarming for the banks is that revenue in the second half of the year crashed 40 percent from the first half and was down almost a fifth from a year earlier.

That's why the pressure is on FICC. By comparison, equities income rose 17 percent last year and advisory revenues grew by just over a tenth across the 11 banks.

The slump has been blamed on low volumes after the Federal Reserve said it would start putting the brakes on buying bonds under its programme to stimulate the U.S. economy.

But tougher global rules forcing banks to hold more capital against risky assets also squeezed margins and threatens to cause more long-lasting damage. "Last year was a double whammy," said Seb Walker, partner at investment banking consultancy Tricumen.

Governments across the world are determined avoid a repeat of the crisis which exploded in 2008 when taxpayers had to bail out a series of banks at huge expense.

"Basel III" rules being phased in require banks to squirrel away more of their profits and hold more reserves so that they can absorb future losses without seeking public help.

They also apply higher risk weightings to loans, and require banks to trade more through exchanges and central counterparties rather than directly between each other. These exchanges require them to put up more collateral.

Interest rates revenues were particularly hit by these rules, especially for repurchase agreements ("repos"), government bonds and swaps, which are some of the most heavily traded derivatives contracts.

Activity in 2014 already looks to be down on the strong start seen last year, unsettling bankers who know that often the first quarter is the busiest period. Kian Abouhossein, analyst at JPMorgan, estimated this week that FICC revenues will be down 16 percent in the first quarter.

"The challenge for a bank is that fixed income is a complex, messy business," Tricumen's Walker said, citing the wide variety of products and their different risk profiles and capital requirements.

"To make the right decisions you have to have a lot of good data about your business and predict the actions of others. So they need to look at their businesses segment by segment and decide where to compete and to what extent, and where to leave the market for others," he said.

Analysts said few fixed income businesses are likely to have delivered a return on equity (RoE) last year above investment banks' cost of equity, estimated at about 12 percent, meaning they are not putting their share and bond holders' capital to good use.

Walker estimated that fixed income business typically had pre-tax RoE of between 7 and 12 percent, although individual segments could range from negative to more than 17 percent.

NO LONGER A REVENUE CHASE

Executives at several banks have recently acknowledged when announcing results that the fixed income landscape could be reshaped - but none thought it would be at their expense.

"We expect that fixed income after some adjustment will be a good business," JPMorgan (>> JPMorgan Chase & Co.) boss Jamie Dimon told analysts. "We think a lot of these trends are cyclical, not secular and that's how we are positioned for it."

Banks such as JPMorgan and Bank of America (>> Bank of America Corp) benefit from their large balance sheets, which give them greater capability to maintain fixed income desks during lean periods.

But European rivals such as Deutsche Bank and Barclays are under pressure to meet tough capital and leverage rules earlier and appear to be losing share to the big U.S. names.

The rates market malaise has also been deeper in Europe than in the United States. Positive effects of when the European Central Bank pumped more than 1 trillion euros of cheap three-year loans into the banking system in late 2011 and early 2012 are fading, hitting banks based in Europe harder.

Deutsche, Barclays, Credit Suisse (>> Credit Suisse Group AG), HSBC (>> HSBC Holdings plc) and BNP Paribas (>> BNP PARIBAS) are expected to continue to pull back from lines that were unprofitable or where they lack sufficient size, analysts and bankers said.

Anshu Jain, co-CEO of Deutsche Bank, admitted that after years of chasing revenues across all products to win market share, there has been a shift in focus.

"We could afford to carry those businesses in the past; we no longer can. We are utterly focused now on bottom-line performance of fixed income," he told analysts. "Revenue impact, yes; market share, client impact, no."

Last week's results from UBS - which racked up huge losses during the financial crisis that prompted a state bailout - may have offered some encouragement to others to take action.

Only 18 percent of revenue at UBS's streamlined investment bank last year came from FICC, compared with 45 percent in 2010. But equities income has jumped, and operating profit was up slightly from three years ago as expenses tumbled 36 percent in a division that now has 5,200 fewer staff.

Bankers said firms face a delicate balancing act in search of the "sweet spot" where they have enough scale and resources, but are not too bloated and carrying hefty costs that hurt returns. As ever, they also have eyes on the competition, and the likes of JPMorgan and Goldman Sachs appear confident they will win more business at better margins when rivals retreat.

"A lot of products weren't making money and all banks are cutting back in areas they are not strong. So a lot are thinking whether to get out or stick it out," one senior banker said.

(editing by David Stamp)

By Steve Slater