Here are Monday’s biggest percentage gainers and losers in morning trading, along with top volume leaders, among companies with a market cap between $50 million and $750 million:

Biggest percentage gainers:

• Pyramid Oil Co. (AMEX:PDO) up 21.1% to $5.75 on heavier-than-average volume.
• ChemGenex Pharmaceuticals Ltd. (Nasdaq:CXSP) up 16.17%, or $1.74, to $12.50.
• FPB Bancorp, Inc. (Nasdaq:FPBI) up 15.39%, or $1.25, to $9.37.

Biggest percentage losers:

• Aladdin Knowledge Systems Ltd. (Nasdaq:ALDN) down 23% on news that it reported first-quarter earnings that missed analysts’ estimates by a penny and news that it lowered its fiscal 2008 earnings estimate.
• MedCath Corp. (Nasdaq:MDTH) down 18.25% to $18.82 after the Charlotte, N.C.-based healthcare provider estimated its second-quarter and fiscal 2008 earnings far below Wall Street expectations.
• Qiao Xing Mobile Communication Co., Ltd. (NYSE:QXM) down 16.51% to $6.42 after the China-based cell phone maker reported before Monday’s opening bell that its fourth-quarter revenue declined to $102.4 million from $103.9 million a year earlier.

Volume leaders:

• Packeteer Inc. (Nasdaq:PKTR), 4.86 million shares traded versus average of 412,000 shares.
• Emcore Corp. (Nasdaq:EMKR), 627,420 million shares traded compared with average of 4 million shares.
• Briggs & Stratton Corp. (NYSE:BGG) 598,227 shares traded versus average of 791,000 shares.