It's a bit tricky to add one, the book is the best type of long term storage at the moment. I'll make the game open source in a while though, so everything will be possible!
Ah, no worries. Perhaps dragging a fish to the top of the screen could directly generate a koi code then? Then I could export fish and keep them stored in a directory in my filesystem instead?
**Edit:** Dragging an dropping a koi code into the game doesn't do anything. The game goes lighter in colour, but then returns to normal after I drop it and I don't get another fish. I'm on Linux / Ubuntu 20.10.