So you’ve got a big, healthy refugium attached to your main tank. Just sitting there, without much movement in it (well, aside from thousands of little scurrying pods). Especially if your main tank is chock full of fish, you might start to wonder: Could you keep more fish down in the fuge?
The best answer to start with is yes, maybe.
What’s the big reason for wanting to put fish in there in the first place? If it’s because there is no more room in the main tank, then you might want to opt out--the bioload might already be too high to add yet more fish!
If you want to add fish just to “spice up” the fuge--add movement--remember that this is not a place for active reef fish. Not only are refugia a bit smaller than the main tank (though they don’t have to be!), they also are often densely planted with macroalgae. This means that, for the most part, only small fish will “fit” in there comfortably. However, it’s usually the smaller fishes that are the most voracious pod eaters. In other words, putting such a fish where your pods are concentrated could spell the end of a self-sustaining pod population. Similarly, an herbivorous fish could wipe out all of your macros in short time.
So what could go in the fuge? Smallish, relatively inactive carnivorous (non-pod eating) fishes might work. For example, a frogfish or dwarf lionfish might be great there (especially because they likely could not go in your main tank). A clingfish, hawkfish or Bangaii cardinalfish might work as well!
The important things to consider here is (1) whether or not the fuge environment provides the right type/amount of living space and (2) whether or not the fish could deplete the pod or macro population!