The Goldfish expansion adds 4 goldfish to the base game, each with a new unique action. There's also a Net to help you with its own special action. The Castle expansion is used together with the Goldfish expansion for an even bigger aquarium. It has (you've guessed it) a castle as well as an extra fish of each species which means larger schools and higher points targets to aim for. Each expansion consists of 5 cards plus a rules card and both expansions will fit in the base game box.