SOFIA (Bulgaria), February 18 (SeeNews) - The Bulgarian Stock Exchange's blue-chip SOFIX index rose 0.15% to 500.53 points on Thursday, mainly supported by a 2.76% increase in the share price of poultry producer Gradus [BUL:GR6] and 2.63% rise in the shares of diversified group Stara Planina Hold [BUL:SPH], bourse data showed.