Jim Platz and Alejandro Aguilar joined American Century Investments as vice presidents and senior portfolio managers in its Mountain View, Calif., fixed-income division. Mr. Platz is co-manager of the $1.4 billion American Century Stable Asset fund. He had been a vice president and senior portfolio manager in the San Francisco office of Standish Mellon Asset Management; a spokesman said Mr. Platz will be replaced. Mr. Aguilar will manage the $960 million American Century Short-Term Government fund in addition to the mortgage portion of the company's multi-sector bond portfolios. He fills a longtime vacancy. Mr. Aguilar had been an investment officer in the fixed-income division of the California Public Employees' Retirement System, Sacramento; CalPERS currently is recruiting to fill Mr. Aguilar's job.