Ocean Aquarium

Ocean Aquarium is a calm idle game drawn as one enormous tank seen from the visitors' side of the glass, late in the evening. Teal water fades to indigo, light ripples over the sand, kelp sways with the filter, and a school of neon tetras turns all at once like a single animal. Tap anywhere in the water and a flake of food drifts down; whichever fish is nearest breaks off and goes for it. Fed fish are happy fish, and happy fish leave pearls. Tap a fish directly and it shows off — a barrel roll, a spin, a pufferfish twice its own size — for a burst of pearls and a ripple of camera flashes from the crowd.

Pearls buy the tank. Twelve species arrive in turn, each with its own way of moving: tetras and tangs shoal, angelfish drift with their fins trailing behind them, seahorses hook a tail round a kelp blade and stay put, jellies pulse up and down like lamps, a stingray flies along the sand, a sea turtle comes to the glass to look at the visitors, and an octopus hides in the furniture until you spot it. Coral shelves, a sunken rowing boat, a treasure chest, a diver's helmet, a sand castle and a bed of glowing anemones fill out the scene and lift the rate, while filters, lights and an auto feeder keep the water turning over while you are away. A ticket booth brings more visitors to the glass, and more visitors means more pearls. Seven expansions make the tank taller and wider, and the last one is built for a whale shark.

Things happen in a tank this size. A feeding frenzy doubles everything for half a minute, a jellyfish bloom drifts through and wants tapping, a diver gets lost and needs guiding to the chest, a ring of bubbles crosses the glass, and now and then a shy octopus tucks itself into the decor. When a wing has run its course, open a new one: the tank empties, the lifetime pearls turn into black pearls that lift every pearl you will ever earn again, and a new hall opens with its own water — a kelp forest, a bioluminescent deep, an arctic shelf. Progress keeps running for up to eight hours while the tab is closed, and a card tells you what the fish got up to. A species album fills in as each one arrives, and the tank saves itself between visits.