For a while there I was off fishing a couple of times a week as part of my "Strange Fish Challenge". On one occasion I bought a dozen minnows with the plan to get out early in the morning to fish before local layabouts got to a popular site.
I put the minnows, in a minnow bucket of course, into the backyard pond for the night. Naturally the top came off, the minnows escaped and I had to round them up.
A few had died. Fish generally don't do well with changes in temperature, water quality etc. The survivors I recaptured, put back in the bucket and basically never caught anything with them. I don't remember if I let some go or not, it was a discouraging day.
Fast forward to October. I'm getting the pond ready for winter. The pump comes out. I get as many leaves and such out as I can, so that the water is not nasty next Spring. I usually bail the pond out to the bottom, but this year there seems to be a frog living and hibernating there so I contented myself with simply bailing a few buckets out and replacing with clean water from the rain barrel.
But wait a minute, what's that flopping in the grass? It turns out that one minnow had survived, nay, had thrived in the pond for several months! Crummy water quality, marauding raccoons, my mucking about with a net clearing out leaves and such....and he's still there!
This fellow deserved to live, so I tossed him back into the pond until the next day when I could launch a suitable rescue operation.
I carefully emptied the pond to the point where I could net him. A quick photo op...
My fish consultant ID'd this as a Blunt Nosed Minnow (Pimephales notatus). They are pretty common state wide and favor streams and small rivers. So into a ready container and off to a nearby small stream. Here Survivor Minnow is contemplating his new home. I wish him well.