I worked at a place that did this for two months. After I could no longer take torturing fish, I left and took a few dozen fatheads with me. The knowledge I learned and the fish I took home began my life keeping aquariums and ponds. Before then, I had only had a few goldfish. Fathead minnows and sometimes rosy red minnows are sold as bait to hook onto lines to catch larger fish.
Many anglers only learn about small fish as bait.
I do not fish. Piranha, oscars, other large piscivorus and omnivorous fish, aquatic turtles, water snakes, semi-aquatic lizards, and other animals all may eat these fish. Since rosy reds stay smaller than goldfish, they are better suited to feeding smaller animals. I am one of the few. These are my favorite fish.