The 25 largest mutual fund groups keep shrinking in the war of attrition that is the investment world right now.

The Financial Research Corp. today released its rankings based on net flows of money in January as well as assets under management.

Malvern's Vanguard Group continues as the biggest mutual fund family as ranked by assets. It had $787 billion in January, down about 4 percent from $819 billion in December. A year earlier, Vanguard has $1.04 trillion in assets. That's makes for a 24 percent decline year over year.

American Funds, of Los Angeles, is No. 2 with $687 billion in assets, followed by Boston's Fidelity Distributors with $464 billion.

The only fund group that increased assets between December and January? Pimco Funds, of Newport Beach, Calif., which had $212 billion at the end of January.

Assets for the mutual fund industry have fallen 33 percent over the last year, according to Financial Research, a Boston consulting firm. The industry had $5.34 trillion under management at the end of January.

But the industry also had a net inflow of $22.3 billion in January, with most of that flooding into corporate bond funds.