There's a tag community-aquarium which mostly seems to be a special fish case of compatibility. We don't have special compatibility tags for other animals, so it seems inconsistent to have a special case just for fish.
I've looked at the questions that are tagged with this tag and they consist of:
- Which fishes can live together with neons?
- What non-fish animals are safest for my freshwater aquarium?
- Which shrimp will co-exist with my loaches and schooling fish?
- Giant gourami tolerate tank mates?
- Can I put any other fish in with a male betta?
- Which smaller fish to add to a 60-gal. tank of danios, corydoras and tetras?
which are all covered by the compatibility tag and
- How can I resolve a fish conflict in my aquarium?
- Why is my tetra attacking other tetras when they swim nearby?
which are covered by the behavior tag (the first one possibly also by compatibility).
I can't think of a use for the community-aquarium tag that isn't covered by compatibility, behavior, introducing-pets or socializing.