Vanguard today said it closed its $1.5 billion Vanguard Convertible Securities Fund to new accounts, after seeing the fund's assets rise 73 percent in the last five months due to net cash flow and market appreciation.

The Valley Forge mutual fund company said the closing is effective immediately and includes a $25,000 annual investment limit on current retail accounts.

"The board of directors regularly monitors cash flow into Vanguard's funds and takes action when assets reach levels that could impede advisors' ability to implement their investment strategies effectively," Bill McNabb, Vanguard's chief exective officer, said in a statement.

The fund's investment advisor is Oaktree Capital Management L.P. of Los Angeles. Oaktree has managed the fund since 1996.

Five other Vanguard funds are currently closed: Vanguard Primecap Fund, Vanguard Capital Opportunity Fund, Vanguard Admiral Treasury Money Market Fund, Vanguard Treasury Money Market Fund, and Vanguard Federal Money Market Fund.    - Reid Kanaley