The Sensex at the Bombay Stock Exchange fell 90 points, or 0.6 per cent, to 15,759 in opening trade, this morning, on fresh selling by investors, amid domestic growth concerns and weak regional bourses.Later, after falling as much as 171 points at one stage, the Sensex retrieved much of the lost ground, to stand just 13 points in negative territory, at 15,836 in afternoon trade.Other Asian markets in Hong Kong, Indonesia, Singapore, South Korea and Taiwan were down by between 0.3 percent and 1 percent, on renewed worries about the fallout of the European sovereign debt crisis.