Fidelity Investments, the largest U.S. mutual fund company, has raised its stake in Apple Computer to 12.29 percent from 5.75 percent of outstanding shares, Bloomberg reported. The Boston, Massachusetts-based fund company held 16,665,531 common shares as of July 31, according to a regulatory filing. That includes $69.9 million in debt that can be converted into 2,393,033 common shares.