Massachusetts Pension Reserves Investment Management board in Boston March 16 hired BlackRock to manage a $1.3 billion domestic fixed-income assignment. The money previously was managed by Putnam Investments, which was terminated last November. The $25 billion fund received 24 responses to its proposal. Separately, Mellon Trust was hired as custodian for the PRIM trust, replacing State Street Bank, which rebid. PRIM systematically re-evaluates custodial services every three years.