To add any fish or decorative element you've got to buy things with coins you earn from beating the puzzles you see at the bottom right of the screen. Solve it and you win a prize; solve it in very few moves and you'll get some extra money that should help a lot when you go to invest in your aquarium. To be able to reach your objective in each puzzle you've got to match three or more items in the same color and get the set amount of points or objectives.
In Fishdom you can add dozens of fish of all kinds that will freely roam your installations. There are fish in every color and size to enjoy watching as they swim around your aquarium. In addition you can get decorative objects to liven up your aquarium and give its small residents a new view of their home.
Enjoy this fun adventure by decorating your aquarium and solving all kinds of puzzles, where you have to show off your skills by finding the right answer before time runs out.