there is no need to use feeder fish. they provide little to no nutritional value, and commonly transfer parasites and disease.
if you are looking to suppliment your fishes diet, there is a host of available dry, frozen, freeze dried and gel foods you can use. alternatively you can also use live blackworms, mealworms, nightcrawlers, and crickets. all of which are better for the fish, and less likely to transfer diseases.