And Then There Were None

Son of a fish!!!

The murderous stripey fish is no longer in the tank.  There are only three possible explanations:
1) this was his plan all along.  He had his escape planned from the beginning.  He knew the fin would be pointed at him once all of the other fish were dead and eaten.  There was a little water on the floor, but I still doubt he could make it to the door.  In this scenario, he is a fish criminal mastermind, so perhaps we will find some aquatic tunnel below the rocks.
2) one of the plastic seaweed thingies is actually a fish-eating sea creature.  Or maybe one of the larger rocks.
3) he killed and ate himself, possibly because of the crushing guilt.

There are no other plausible explanations.