I left a single zebra danio in a tank that was turned off, no light, no food, no water changes, nothing, nada for close to 7 months.
To be fair, I purchased zebra danios to be my cycling fish, and this dude just wouldn't die. It wasn't a newbie mistake, I was well aware it was bad, but the dude just wouldn't die.
I still have him today, and I respect him that much more.
its those kind of fish that you love so much and don't want to lose because they survived everything lol