Well, angels grow to about 5 inches and harlequin rasboras grow to about 1.5 - 2 inches. If angels are grown by themselves (with no other fish species with them) and then they're put inside a tank with fish much smaller than themselves, they may be aggressive toward the smaller fish and even treat it as food. And although I don't think an angel would be able to eat a 2 inch fish, it could still be aggressive toward it. Always look at the fish's mouth - if it's large enough to eat any other fish you might have, there's a good change it can do so. However, I personally have 2 angels that were raised from babies with neon tetras (neons are about 1 inch) and they are not aggressive toward the neons. I think this is because they're used to them.