Aquarium Rainbowfish is a small expansion for Aquarium which features the special Rainbowfish. This expansion is a promotional expansion and it is not for sale. Rules for the Rainbowfish: The rainbowfish can be just be added to the deck but beware because they are pretty powerfull! The best way to use the rainbowfish is to give each player one at the start of the game instead of the normal fish of size 1. The rainbowfish is a fish of size 1 (so it eats only 1 unit of food each feeding time) but it's worth 1 extra star at the end of the game. The rainbowfish can be used as a fish of size 1 of one of the four colours so it makes it easier to score your bonuspoints at the end of the game (if you keep it alive till then!) or can be used to start an early breeding tank (but then you won't profit from the possible extra stars)