Castano will start Friday's game against the Giants, Jordan McPherson of the Miami Herald reports.
Castano was called up by the Marlins on Sunday, and he'll make his season debut in the series opener at home against San Francisco. The southpaw is unlikely to serve as a regular starter for Miami, but he posted a 3.03 ERA and 1.38 WHIP in 29.2 innings during seven appearances (six starts) in 2020.