Yes, rainbow sharks can eat other fish. Rainbow sharks will typically only eat small and defenseless fish that accidentally venture to the bottom of the tank. Aside from that, rainbow sharks generally don’t purposely prey on other fish or other aquatic animals.
Moreover, these bottom-dwellers are unlikely to swim to the top of the tank to chase other fish.
However, that doesn’t mean rainbow sharks are completely harmless. Because they’re very territorial, they won’t hesitate to attack other fish that invade their territory. They’re particularly hostile towards other rainbow sharks, freshwater sharks, and bottom-dwelling fish.
Rainbow sharks are known to chase smaller rivals and fight them. Try keeping your rainbow sharks with mid and top-level dwellers that can fend for themselves when attacked.