Mutual fund giant Fidelity Investments on Thursday said it took in a record amount of revenue but reported lower profit in 2015 as it spent more on staffing and technology.

Closely-held Fidelity, known for managing millions of retirement and college savings plans, said operating income fell 6 percent to $3.2 billion in 2015.

At the same time revenue climbed 6 percent to $15.9 billion. Company expenses totaled $12.7 billion in 2015, 10 percent more than in the prior year because of the cost of employees and computer systems, according to an annual report e-mailed by a spokesman.

Fidelity, which has been losing ground to rivals like Vanguard Group and BlackRock Inc, said total assets under management grew 1 percent to $2.04 trillion in 2015.

Founded and still run by the family of CEO Abigail Johnson, Fidelity has long been known for its star stockpickers like Will Danoff, manager of the $103 billion Fidelity Contrafund.

But last year investors took $18.8 billion out of Fidelity's actively-managed stock portfolios, reflecting their growing taste for less-expensive index funds.

Across all products it administers, Fidelity said net deposits of investor cash totaled $190.8 billion. That was down slightly from $210.3 billion in 2014, though that year's figure was boosted by an administrative change.

Overall Fidelity said its funds performed better in 2015 than in 2014. Last year the firm's mutual funds beat 72 percent of peers for the trailing one-year period. In 2014, 66 percent of Fidelity's funds beat peers on the same basis, Fidelity said.

In a letter to the company's shareholders, Fidelity CEO Johnson said during the year customers sought its assistance as never before because of volatile markets, and that it handled the increased activity with no disruptions in service. She called this "a testament to the investments we have made in systems and technology."