At the beginning of the round, current catcher places the Emerald fish on any door in the game.

Once any penguin (even the catcher) goes through the door with the Emerald fish, he takes the fish for himself

If any penguin runs into (or vice versa) the penguin with Emerald fish, the other penguin gets the Emerald fish. This way, the Emerald fish can travel between penguins multiple times during the round.

Once the round ends, the penguin holding the fish receives the Emerald fish point card (worth 3 points at the end of the game)