Morgan Stanley ( MS) continued to talk about how safe it is in its first-quarter earnings report Wednesday, but that does not appear to tell the whole story about why it made less money than Goldman Sachs ( GS).

Morgan Stanley reported a loss in the first quarter, in contrast to other large banks such as Goldman, Bank of America ( BAC) and JPMorgan Chase ( JPM). But like those banks, and others, including Citigroup ( C), it got a big boost to revenues from fixed-income trading.

A large portion of the gain looks to come from banks acting as middlemen, capitalizing on increased trading activity and higher "spreads" -- the difference between what a buyer will pay and a seller will offer for a particular bond, according to Tim Sangston, fixed-income consultant at Greenwich Associates.

"It's kind of a double whammy, where volumes are up, and the quality of the volumes are improving from the dealers' point of view," Sangston says.

But Morgan Stanley did not do as well as its rivals in fixed-income trading, judging from an exchange between CFO Colm Kelleher and BofA analyst Guy Moszkowski during the company's earnings call on Wednesday.

Referring to fixed income, Moszkowski alluded to some calculations he had made in order to compare the results of different firms, and then said, "it still seems like you're running significantly lower than Goldman, Citi or JPMorgan, and I'm wondering, despite the fact that you say you're seeing improvement in market share, whether there's something in terms of risk appetite or something else that might be driving that."

If you liked this article you might like

Bank Stocks Move Higher as Fed Decides to Start Unwinding Balance Sheet

Bank Stocks Move Higher Ahead of Federal Reserve Meeting

Morgan Stanley Is Using Snapchat to Recruit College Students and Make Them Rich

WeWork Claims Work as a Concept in Suit Against Chinese 'Copycat'

Citi Trading Revenue May Dive 15% as Goldman Cites 'Challenging' Bond Market