Castano was recalled from the Marlins' alternate training site Sunday.
The 26-year-old didn't make Miami's Opening Day roster but will join the big-league club to close the second weekend of the season. Castano made his major-league debut last season and had a 3.03 ERA, 1.38 WHIP and 12:11 K:BB over 29.2 innings for the Marlins. He could be an option to serve as a bulk reliever behind opener John Curtiss in Sunday's game against the Mets.