There is nothing to keep alive here. No hunger bar, no water quality, no fish that dies if you close the tab for a fortnight. Every real aquarium is a small unpaid job; this one is only the good part — the standing in front of it.

The six species are invented, and so are their names. They swim by steering rather than by animation: each fish wants to keep a comfortable distance from the glass, drifts towards whatever is interesting, and is nudged along by its neighbours if it is the sort that shoals. That is why they never quite repeat themselves.

Your tank lives in this browser and nowhere else. It will be here when you come back, and it will look exactly as you left it.