Castano has made the Marlins' Opening Day roster, Jordan McPherson of the Miami Herald reports.
Castano was optioned to Triple-A Jacksonville in March, but he'll rejoin the major-league club as part of the Opening Day bullpen. The southpaw made five appearances (four starts) for the Marlins last year and logged a 4.87 ERA and 1.48 WHIP in 20.1 innings.