Total revenue was $82.3 billion (49.56 billion pound) in the first six months of the year, compared with $86.8 billion in the same period a year earlier, consultancy Coalition said.

Fixed income, currencies and commodities (FICC) was the worst performing area, with revenue down 13 percent year-on-year to $39.6 billion, according to the figures.

Coalition said the downturn in FICC reflected structural and cyclical pressures facing banks, including tougher regulations that require banks to hold more capital against risky assets and a lack of volatility in financial markets.

Foreign exchange was the poorest line of business, with revenues down over a third from the previous year, its largest year-on-year decline since 2008.

Commodities trading outperformed for the second quarter running, however, with revenue up by more than a fifth.

Revenue from banks' equity business was also lower in the first half, falling 4 percent year-on-year to total $21.6 billion. Weakness in derivatives led the decline, offsetting higher demand for prime services.

A surge in mergers and acquisitions (M&A) and stock market listings in the first half lifted revenue at investment banking divisions, whose staff advise on deals, by 11 percent to $21.1 billion.

M&A volumes reached their highest level in seven years in the year to end-June, while activity in equity capital markets rose 16 percent.

A number of investment banks, including Barclays (>> Barclays PLC), Deutsche Bank (>> Deutsche Bank AG) and UBS (>> UBS AG) are cutting costs to counter the slump in trading revenues and the stricter capital requirements that are making some areas unprofitable.

Many have shed jobs as part of that effort and Coalition said headcount dipped 4 percent in the first half.

Coalition, which tracks the performance of Bank of America Merrill Lynch (>> Bank of America Corp), Barclays, BNP Paribas (>> BNP PARIBAS), Citi (>> Citigroup Inc), Credit Suisse (>> Credit Suisse Group AG), Deutsche Bank, Goldman Sachs (>> Goldman Sachs Group Inc), JPMorgan (>> JPMorgan Chase & Co.), Morgan Stanley (>> Morgan Stanley) and UBS, also gave forecasts for full-year revenue.

Annual revenue across major investment banks was expected to total $150.7 billion, a 2 percent decline on 2013.

(Reporting by Clare Hutchison; Editing by Mark Potter)