In the mirror universe, the Denobulans were a subject species of the Terran Empire. It is unknown when they submitted to the empire; however, it occurred some time prior to 2155 as there were Denobulans already serving on board Imperial Starfleet vessels by that time. Several Denobulans were rescued from slavery in the mines of Korvat by Keiko Ishikawa in 2375. (DS9 - Mirror Universe novel: Saturn's Children)