After the stock market's fourth-quarter bang, investors expected a bigger boom than they got from leading custody banks State Street and Bank of New York Mellon .

The rally did lead to more fees for the quarter, but not enough to impress investors. Shares of BNY Mellon were unchanged, while State Street fell more than 3 percent.

The two banks' stocks had gained more than 20 percent in the past three months.

The environment is clearly improving -- it's not perfect, but both stocks will chug along, Stifel Nicolaus & Co analyst Jeffrey Hopson said.

Bank of New York Mellon, the world's biggest custody bank, said fourth-quarter profit from operations increased 10 percent as two acquisitions from last year bolstered fee income. Operational earnings per share of 59 cents were slightly ahead of analysts' estimates of 57 cents.

The fourth quarter was the best for fee income since the start of the financial crisis in 2008, Chief Executive Officer Robert Kelly told analysts on a conference call.

But Nomura analyst Glenn Schorr said that despite the pretty good quarter at Bank of New York Mellon, the stock has had a big run and could soften given slight disappointments on expenses and assets.

Assets under custody, the bulk of which are in fixed income, grew only 2 percent during the quarter.

At slightly smaller rival State Street, earnings per share before special items rose, beating Wall Street's expectations by a penny as fee revenue increased 10 percent to $1.7 billion.

In the custody business, the company ranks behind BNY Mellon and JPMorgan Chase & Co .

Low interest rates have pressured revenue growth at State Street and BNY Mellon. With the Federal Reserve's main lending rate near zero since 2008, custody banks are forced to waive fees they collect on money-market funds.

Fourth-quarter results at the much-smaller Northern Trust Corp offered a more difficult picture. The Chicago trust bank said fourth-quarter profit fell 22 percent, hurt by low interest rates.

Earnings per share of 64 cents missed analysts' estimates of 71 cents.

Northern Trust assets under management fell 2 percent from the September quarter, but assets under custody rose 4 percent.

Shares of Northern Trust were down more than 3 percent in morning trading.

(Reporting by Svea Herbst-Bayliss; Editing by Lisa Von Ahn)