Here are Thursday’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:

• Gibraltar Industries, Inc. (Nasdaq:ROCK), up 28.8% to $14.23 after the Buffalo-based maker of building products posted first-quarter earnings of $6.7 million, or $0.22 per share, topping Wall Street’s expectation of earning $0.14 per share. A year earlier, Gibraltar posted earnings of $6.2 million, or $0.21 per share.
• Central Garden & Pet Co. (Nasdaq:CENT), up 28.4% to $5.39 after the Walnut Creek, Calif.-based supplier of pet supplies and lawn products reported better-than-expected revenue for the second quarter.
• R.H. Donnelley Corp. (NYSE:RHD), up 27.7% to $8.15 after the Yellow Pages publisher reported first-quarter revenue of $674.7 million versus $661.3 million during the same time a year ago. Wall Street analysts anticipated $664.5 million in revenue.

Biggest percentage losers:

• Kingsway Financial Services Inc. (NYSE:KFS), down 29.2% to $10.02 after the insurance holding company reported a first-quarter loss of $34.4 million, or $0.62 per share, versus analysts’ expectation of earning $0.38 per share. A year earlier, the Canada-based firm posted a profit of $19.6 million, or $0.35 per share.
• Hardinge Inc. (Nasdaq:HDNG), down 19.4% to $13.85 after the Elmira, N.Y.-based company posted a first-quarter loss of $0.7 million, or $0.06 per share, which widely missed Wall Street’s estimate of earning $0.34 per share. During the prior-year period, Hardinge posted a profit of $5.3 million, or $0.60 per share.
• TurboChef Technologies, Inc. (Nasdaq:OVEN), down 17% to $6.51 after the Atlanta-based provider of food preparation products posted a wider-than-expected loss for the first quarter.

Volume leaders:

• R.H. Donnelley Corp. (NYSE:RHD), 8.5 million shares traded versus average of 1.8 million shares.
• Hovnanian Enterprises, Inc. (NYSE:HOV), 6.5 million shares traded compared with average of 2.6 million shares.
• MCG Capital Corp. (Nasdaq:MCGC), 4.4 million shares traded versus average of 1.3 million shares.