Can you feed real fish?

I use to feed mine pellets (95%) and guppy's from time to time .
 
I have heard that sushi consumed by humans should be frozen first in order to kill any parasites living within the tissue of the fish. I guess if you were to feed fish to other fish, that the same rule should apply. But now that I think of it what happens to all the fish that eat live guppies/goldfish?

Oh well - just putting in my two cents.
 
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