The BSE benchmark Sensex lost over 68 points in opening trade today on fresh selling by funds and retail investors amid a weak trend on other Asian bourses.The 30-share barometer, which gained 43.63 points in the previous session, fell by to 18,351 in the first few minutes of trade today as auto, FMCG, capital goods and banking stocks retreated.The wide-based National Stock Exchange Nifty index moved down by 24 points to 5,508 points.In other markets in Asia, Hong Kong's Hang Seng index was trading lower by 0.70 per cent, while Japan's Nikkei was marginally up by 0.23 per cent in morning trade today.In the US, the Dow Jones Industrial Average closed 0.50 per cent lower on Monday.