Upside-down fish

My first fish spotting, I found these small fish in an isolated puddle about 30 feet from the river. There were quite a few of them in a puddle of only a few square feet. Most of them were floating on their backs at the top of the puddle and appeared dead, but when they were disturbed they swam away. I caught this one with a dip net and put it in a pan of water. For a while it swam around right-side-up, but I wasn't able to get a picture of that. Eventually, it went upside-down and would float and swim in that orientation.