Thought I’d share this fish compatibility infographic, published by Petco. I didn’t create it, I’m just sharing it, because I think it is pretty good. Save it to your phone so you can scan quickly the next time you’re in a local fish store.
Update 10/24: As with any summary, this is no substitute for detailed research. Anytime advice is generalized (including that generalization), one loses something in terms of detail. Take, for instance, the section on eels–some eels are flat out not compatible with anything that swims and fits in their mouths while hunting. So despite what it says on the chart here, use this cautiously as a starting point or refresh of your research, not as a substitute for that research.