On the day this week that UBS made the striking announcement that it is largely getting out of bond trading, the Swiss bank's German rival, Deutsche Bank, said it reaped a windfall on the business.

The banks' differing fortunes sheds light on how the securities industry's biggest business works and the wrenching changes it is undergoing. Even though most banks experienced a third quarter bounce in the fixed income business, a variety of factors, including regulatory changes that may crimp already modest returns, ultimately could prompt others to follow UBS's lead.