There is really no reason to feeders except as the ocassional treat.
Various live fish and fry can be used for foods.Caution here unless you raise them
any commercialy bought feeders usually rosie reds/tuffies (the albino form of fat head minnows),
guppies,bait minnows etc.need to be quarantined before feeding them to your fish for several reasons.
reason 1 They are kept in horrible conditions
reason 2 They are often diseased
reason 3 They often are carriers of parasites
During quarantine dispose of the obviously sick or diseased.The remaining ones feed quality
foods a healthy feeder is of course better for your fish.
Goldfish just generaly are poor feeders and should be avoided. they are oily not very nutritious and constant feed of them causes faty deposits on the liver leading to premature deaths.They also contain very high levels of Thiaminase a destroying hormone.While many fish used as feeders contain this goldfish seem to have an abundance of it.Another issue is a spine at the front of the dorsal fin which can lead to problems if the goldfish is swollowed the wrong way (tailfirst).Yet another reason not to use goldfish,goldfish farms utilize copper meds in suspension form to combat diseases in the feeders associated with overcrowding.These copper meds are retained by the feeders for long periods after they leave the farms.Most lfs invariably retain all or part of the feeders shipping water when the feeders are loaded into their bins/tanks. And copper does not dissapate from a closed system.
Now then what can we feed them? You actually have several options and They will be listed below
The freezer at your local fish store is a smorgasboard of foods which should include
silversides or lancefish
mysis shrimp
brine shrimp
krill
bloodworms
tubifex worms
squid
beefheart
Simply thaw and feed
Pellitized foods
Can be found in various diameters and forms include sinking and floating pellets and sticks
shrimp pellets
worm pellets
even pellets for cichlids will work
spirulina sticks
brine shrimp sticks
Algae wafers(some eat them some just look at them)