People have put these two fish together, but it isn't a good idea at all. Adding the silver arowana in the same tank as the discus fish will put stress on the fish. The discus fish likes to swim close to the top of the tank and will grow rather large. Furthermore, the arowana will grow rather large and they move around way too much. This could hurt the discus fish if the arowana ran into the fish a lot. I wouldn't recommend it at all.