How big is he? If he's fairly small, you can feed him once every 5 days. Try to make his meals about 10%-15% of his weight. If he's larger, you don't have to worry about the size of the feeder---a small rat once a week is appropriate for a male of any size. Overfeeding isn't good for them, neither is feeding too often; they need to have time to digest in between meals. Do you know his weight and the weight of the rats?