I imagine it helps to have tough skin on your fingers. Most of the bluegill related species I'd catch back in Ohio had very sharp spines. When I was a kid I caught dozens of small catfish from under rocks with a method similar to what you're showing; it only took a day or two before I had an aquarium full of them!

This time of year here in the mountains, brook trout will jump out of the water and land on the rocks when they're trying to get above the waterfalls. Catching them doesn't really require much effort, I just have to wait and then grab them when they're flopping around on the rocks. I set these ones in a pool to keep them wet while I took a picture, then I tossed them back in the water. It's a really cool thing to witness, I'll going to try to get a video of them next week.