What is the differences from a goldfish and a feeder fish?

a goldfish is a feeder fish.

I kind of disagree with the answer above. Yes, goldfish CAN be feeder fish, but they aren't necessarily feeder fish. Feeder fish are really fish that are rather small and are fed to other animals, and that are for some reason thought as not being as precious as other "pet" fish. So a feeder fish and a pet fish are two different kinds of fish, really. Not all goldfish are feeder fish. There are expensive goldfish, more than 10 dollars per fish! Then there are those goldfish breeded to be eaten that are sold as 75 cents per fish. So there are "pet" goldfish and "feeder" goldfish. So, a goldfish is not necessarily a feeder fish.