In addition to the goldfish, you'll also play as a dolphin and a shark. The dolphin starts off as an overworked aquarium star, forced to jump through flaming hoops for food. He escapes from captivity by eating his way through the aquarium and taking revenge on his trainer. The shark is the final playable character, an artificial fish created by scientists to save Earth's oceans. It uses self-replicating nano technology to consume everything in its path and convert their matter into its own. There's no telling how big this shark will get.
There are over 50 levels in the main story mode of the game. There are also 15 more challenging bonus levels to play after the main game has been completed.
There are three main environments to explore in the game: temperate, tropical, and arctic.
There are a wide range of difficulty levels to choose from. On the easiest difficulty enemies do virtually no damage. On the most challenging difficulty enemies will eat you and cause instant level failure.
Two players can play side by side on the same computer. Options allow for split screen (horizontal or vertical) or shared screen (this provides more screen space but constrains the movement of players together).