Happy Aquarium introduces the "Super Sea Shell Hunt"
So how do you get these shells? Well, they show up randomly when you click on the Treasure Chests in the game. And yes, even the chest in the demo tank can get you a shell. When you receive a shell, you'll get the pop-up on the right.
Since Happy Aquarium still has no item storage, the shells will have to be stuck in your tank until you've collected everything. You can also sell the shells for coins. The two ones pictured above, "Blue Shell" and "Green Gold Shell" are listed as "Common" and go for 40 Coins each. The others are harder to get, so they might go for more money.
No other details have been released so far, so we'll just have to stay tuned!