I love animals - they really help my depression. I like keeping fish too, although I don't have an active tank right now (they died when I was on vacation and the power went out for many days...). There are lots of other cool animals you can keep in a small fish tank that might work. I love frogs and newts (fire-belly toads are awesome and available at almost any pet store). Small reptiles are maybe doable too, like a skink or bearded drangon. The downside of these are that you may need to get crickets once a week which is harder than flake fish food but going to the pet store once a week gives you something to do anyways and they're like $2.00 a dozen. I would think any place you could keep fish you could also keep amphibians and small reptiles (other than snakes, which are prone to escape).

Currently I have a russian tortoise and he's fun to watch and take care of. He's not loving like a dog but he counts on me to take care of him and that helps me.