Shares of the first publicly listed U.S. hedge fund soared in early trading Friday, doubling on their opening day.

Fortress Investment Group's LLC's (NYSE: FIG) shares began the day at $35.50 after their initial price per share was set yesterday at $18.50. The initial sale raised $643.3 million. By the late afternoon, Friday, shares were just above $31.

The company trades under the ticker symbol FIG on the New York Stock Exchange

Hedge funds have traditionally worked in a more secretive manner than publicly traded firms, usually allowing only millionaire investors to participate. Their private status does not require them to be subject to fiscal scrutiny as rigorous as that of public traded companies.

The underwriters of the fund, Goldman Sachs and Lehman Brothers, set the initial prices of shares, valuing Fortress at nearly $7.4 billion. The firm earned $192.7 million in 2005, up 68 percent from 2004.

There are about 6,000 hedge funds in the U.S., which manage almost $1.3 billion.