If you buy angelfishes when they are young and raise them with smaller tetras, they won't see them as food when they get larger. However, once they get large, any new fish you add in there, they will chase and try to eat it, even if it doesn't fit in its mouth...but if the new fishes are fast and larger, the angelfishes will give up after a while, thats what happened when I added glass catfishes into my tank with 8 mature angelfishes. They tried to eat the larger glass catfishes and left the smaller neons and cardinal tetras (fishes it grew up with) alone.