Japan\'s key Nikkei index closed at a fresh five-month low Monday, amid concerns on the European debt malaise and slower U.S. economic growth. The benchmark 225-issue Nikkei Stock Average dropped 91.11 points, or 1.04 percent, from Friday to 8,628.13, its lowest finish since March 15. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was down 8.85 points, or 1.18 percent, to 742. 84. On the First Section, declining stocks outnumbered advancing ones 1,231 to 340, with 94 others remaining unchanged. Trading volume on the main section fell to 1,966.06 million shares from Friday\'s 2,047.04 million. Turnover was 1,204.9 billion yen (15.65 billion U.S. dollars).