Happy Aquarium is a so-called social game that can be played on Facebook.

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The player starts out with one fish tank and a couple of fish. The tank has to be cleaned every (real time) day, as well as the fish being fed.

Fish will grow in size over time. Every day fish can be trained by playing a simple mini-game where the fish swims to the left of a course and the player has to click on all the harmful elements such as fishing lines, cat paws and sea mines.

Another daily mini-game is the treasure hunt. Here the player can control one of his or her fish directly with the mouse in order to collect coins in a coral reef.

Coins can be used to buy new fish and decorations for the fishing tank. Aside from coins there's also pearls which allow the player to buy more unique items but who are less easily gained. Additionally Facebook Credits can only be bought with real money and can also be used to bypass pearls. Money can also be used to expand the tank size to allow for more fish per tank or to buy additional tanks.

Players can visit friends to find more coins and collectible items and to clean their bowl for additional experience points and coins. Friends can also be placed on an expedition ship which (when full) can be set to sail out in search of treasure.

Most actions in the game grant the player experience points. Experience points determine the level of the player, high levels unlock more features such as additional fish tanks.

If the player logs in every day for two consecutive weeks he or she gains a frog to place in the aquarium.