A free app for Android, by HappyElements.

In Happy Fish, you can collect rare and colorful varieties of under-the-sea folk for your tank.

There are over 150 kinds of cute fish in this game, and you’ll have the opportunity to care for them by feeding them and ensuring their well-being, all while gaining valuable experience and having a ton of fun in the process. With each level you complete, you’ll earn experience points and gems that can be used to purchase new fish and other items for your aquarium. And if you’re feeling social, you can even visit your friends’ aquariums and feed their fish as well!

The game can be played without an internet connection.