NEW YORK -(Dow Jones)- The much-heralded initial public offering of hedge-fund manager Fortress Investment Group LLC (FIG) didn't disappoint Friday after the stock delivered the best one-day performance so far this year.

The stock closed on the New York Stock Exchange at $31 a share, up 68% from its IPO price of $18.50.

Fortress, which become the first U.S.-listed hedge-fund manager, debuted at $ 35 a share, 89% above its IPO price.

Its first-day trajectory was the biggest since digital storage system company Isilon Systems Inc. (NASDAQ-NMS:ISLN) (ISLN), which soared 78% on its first trading day on the Nasdaq Stock Market late last year.

Fortress's stellar debut capped off the busiest week in the 2007 IPO market so far this year with 13 pricings, the largest since the pre-holiday frenzy when 17 deals were priced the week of December 11.

This week's 13 deals are worth a total of $3.4 billion, based on data by Dealogic.

Fortress's IPO raised more than $634 million, making it the second largest this year behind in-theater advertising firm National CineMedia Inc. (NASDAQ-NMS:NCMI) (NCMI).

National Cinemedia, which began trading on the Nasdaq Stock Market Thursday, raised $798 million.

Fortress sold 34.29 million Class A shares at a price above its expected range of $16.50 to $18.50 set by Goldman Sachs Group Inc. (NYSE:GS) (GS), Lehman Brothers Holdings Inc. (NYSE:LEH) (LEH), Banc of America Corp. (NYSE:BAC) (BAC), Citigroup Inc. (NYSE:C) (C) and Deutsche Bank AG (NYSE:DB) (DB).

In recent weeks, Fortress sold another 55 million class A shares to Japanese securities firm Nomura Holdings Inc. (NYSE:NMR) (NMR) for $888 million.

The deal equates to just over $16 a share, meaning Nomura has almost doubled the value of its investment.

The remaining four IPOs to make their market debut this week had mixed receptions from investors.

Biopharmaceutical company Optimer Pharmaceuticals Inc. (NASDAQ-NMS:OPTR) (OPTR) closed 21.4% higher than its initial public offering price of $8.50.

Optimer, which focuses on anti-infective products, initially targeting gastrointestinal infections and related diseases, opened at $7.50 a share on the Nasdaq Stock Market.

The company's debut was below the expected price range of $8 to $9, and that had been reduced from its initial $12 to $14 range, set by underwriters Piper Jaffray Cos (NYSE:PJC) . (PJC), Jefferies & Co. (NYSE:JEF) (JEF), JMP Securities and Rodman & Renshaw.

VeriChip Corp.'s (NASDAQ-NMS:CHIP) (CHIP) IPO opened and closed at a flat $6.50, in line with its initial public offering price.

The IPO price had been narrowed to $6.50 from the initial range of $6.50 to $ 8.50, set by underwriters Merriman Curhan Ford & Co., C.E. Unterberg, Towbin and Kaufman Bros.

The size of the offering - 3.1 million shares - was also reduced from the expected 4.3 million shares.

The Delray Beach, Florida, company develops, markets and sells radio-frequency identification, or RFID, systems, which are used to identify, find and protect people and assets.

Online auto-parts provider U.S. Auto Parts Network Inc. (NASDAQ-NMS:PRTS) (PRTS) rallied 19% Friday to close at $11.90 after opening 10% above its IPO price of $10.

The Carson, Calif., company sold 10 million shares at the low end of its expected range of $10 to $12 a share set by underwriters RBC Capital Markets, Thomas Weisel Partners LLC (TWPG), Piper Jaffray (NYSE:PJC) and JMP Securities.

Energy group Targa Resources Partners LP (NASDAQ-NMS:NGLS) (NGLS) also racked up double-digit percentage gains, closing at $23.76, 13.1% higher than its IPO price of $21.

Targa sold 16.8 million common units at the top end of the expected range of $ 19 to $21, set by underwriters Citigroup Global Markets Inc. (C), Goldman Sachs & Co. (NYSE:GS) , UBS Securities LLC (UBS) and Merrill Lynch (NYSE:MER) (MER).

The units sold into Targa's offer represent 58% of company. Post IPO, its parent company Targa Resources Inc. will hold 39.9% of the company.

-By Yvonne Ball, Dow Jones Newswires; 201-938-5289; yvonne.ball@dowjones.com

Shares of Optimer Pharmaceuticals Inc. (NASDAQ-NMS:OPTR) (OPTR) closed at $8.50 on Friday, 21.4% higher than the initial public offering price of $7.

("Fortress Deal Caps Off Busy Week For IPO Market" at 5:18 p.m. EST Friday incorrectly said Optimer shares closed 21.4% higher than an IPO price of $8.50.)

    (END) Dow Jones Newswires   02-09-07 1733   Copyright (c) 2007 Dow Jones & Company, Inc.