It's possible, I guess, that the anemone ate the fish. This reminds me of something; do you know that the leading cause of beaver death is being hit by falling trees? Maybe the leading cause of clownfish death is being eaten by it's anemone. There's a certain twisted logic to that...

But, E quadricolor (your rose) is not a natural host for oscellaris clowns, which is what I assume you had. Their natural hosts pack a more powerful sting, which would make me think it's pretty unlikely that the anemone got the fish, unless it was sick or dead already. I bet you find the fish under a rock soon. Watch your ammonia!

Most important, though, WELCOME!! to maast.