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

Biggest percentage gainers:

• Allegiant Travel Co. (Nasdaq:ALGT), up 25.4% to $26.08 after the leisure travel company reported first-quarter operating revenue of $133.1 million, up 58% from $84.3 million a year earlier.
• TranS1 Inc. (Nasdaq:TSON), up 19.9% to $12.79 after news that the FDA has cleared one of their minimally evasive surgery procedures for marketing.
• Seacoast Banking Corp. of Florida (Nasdaq:SBCF), up 13.1% to $10.71 after the bank holding company announced first-quarter net income of $1.8 million, or $0.09 per share, compared with $2.8 million, or $0.14 per share, a year earlier. Wall Street analysts expected earnings of $0.10 per share.

Biggest percentage losers:

• Intevac, Inc. (Nasdaq:IVAC), down 23.4% to $12.63 after the maker hard drive equipment said it expects 2008 revenue in the range of $120 million to $150 million and earning of between a loss of $0.25 per share and a profit of $0.15 per share. Analysts expect revenue of $143.9 million and a profit of $0.09 per share.
 • Digi International Inc. (Nasdaq:DGII), down 20.8% to $8.12 after the Minnetonka, Minn.-based company reported early Tuesday that its second-quarter revenue totaled $43.1 million, which fell short of Wall Street’s expectation of $51.1 million.

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