why not just feed him mice if thats what he likes? at his age and size, one mouse a week is plenty healthy, hes definitely not starving. my adult male who has sired many clutches is only 700-800g and a couple years old. If hes happy with mice, i would just feed him that, no need to get him back on rats. Hes eating f/t so that makes it easy, f/t mice are often cheaper than rats.