Nanoquarium is a real aquarium that lives on your desktop. Pop the tank out and the fish drift across your screen, swimming over your open windows while your clicks pass straight through to your work, or keep it tucked in a cosy corner, always on top. All the fun of a fish tank, none of the water changes.

Built by someone who bred tropical fish for years, so every fish looks, behaves and breeds like the real animal, not a reskin.

A tank that's always alive

It pootles along beside your work whether you're watching or not, so feed it between emails and come back to fry you never saw coming. Tetras shoal, bettas blow bubble nests, corydoras dash up to gulp air, plecos graze the driftwood, shrimp climb the plants. And there's no way to lose: stocking goes by bioload, not fussy fish-count caps, coins tick along while you're away, and nothing ever dies of neglect. Cosy, never punishing.

Collect 200+ real fish

Every fish is based on a real one, with the right shape, size and personality, across three little worlds: a warm tropical community, a cool coldwater tank, and a saltwater reef where coral grows in and clownfish nest in an anemone. 207 species in all, as males and females, long-fin and high-fin strains, pale albinos and inky melanistics, over 500 looks in total, and every fish then gets its own unique markings, so no two are ever quite the same.

Breed your own rare ones

Pair two up, watch them court, and raise the next generation, and every kind does it its own way: scattering eggs through the plants, tucking them in a cave, blowing a bubble raft, or carrying the babies in its mouth. Colours pass down to the fry and drift a little each time (RGB colour-blend genetics), so a line slowly becomes your own. Chase a rare fin shape or a colour nobody else has, and one special fish can be worth a small fortune.

Make it your own

Plant it, scape it and light it however you like: driftwood and stone, lush carpets, a whole shelf of backgrounds, the water tinted and rippling just so. Save your favourite layouts and switch between them, then grow into a whole fishroom of up to ten tanks, each with its own look. Just want to play and decorate? Creative mode hands you everything, unlocked.

How the desktop overlay works

Run the tank any way you like: a frameless window that stays on top in a corner, free-resized to any size, fullscreen, or a click-through overlay where the fish swim over your apps while your clicks pass straight to your work. Tune exactly what shows, from the whole furnished tank down to just the fish on the bare desktop, or anywhere in between. It's so light and quiet you'll forget it's running, so leave it on all day.

Made by an actual fish breeder

Nanoquarium is built by one person who bred tropical fish for years, so the shapes, the sizes, and the way every species behaves and breeds are all drawn from the real thing, not made up. I don't keep tanks any more, and this is the one I get to keep now: all the joy of the hobby with none of the water changes.

At a glance

• Up to 10 tanks + a Creative sandbox (all unlocked)
  
• Window, fullscreen, a tiny corner, or a click-through desktop overlay · system-tray icon (overlay + tray are Windows-only; Linux / Steam Deck run windowed)
  
• Day/night & weather, a travelling fish trader, powerheads & bubble gear, a soft generative soundtrack
  
• Photo + one-click GIF capture · full species bestiary · 59 Steam achievements · Cloud saves
  
• Idle economy: Coins (offline, capped) plus Breeder Points from breeding milestones
  
• Light enough to run on a potato · barely sips power, no graphics card needed