In adventure mode, the player gets two guppies from tanks 1 to 3 and one breeder in tank 4 and he need to take care of them in order to get money to reach the goal - buying egg pieces of special pets, creatures who helps the player in the game.
The player also needs to protect his guppies from evil aliens who wants to kill them. That's why the player has to use a special laser and it's upgrades, except for battles with Gus, a weird fat humanoid alien, in those battles, the player need to feed Gus until it explodes.
There are 5 tanks, in each tank there are 5 levels (except for tank 5, where there is only one level). That means there are 20 pets in adventure mode. Upon the completion of tank 4-5, the player is forced to defeat Cyrax in order to hatch the final egg.
Tank 2 - Gus, Destructor.
Tank 4 - Bilaterus.
Tank 5 - Cyrax (The Alien Boss of Doom).