We have 67 tags that are on only one question. That's a lot. A good bit of these tags are unneeded, though not all.
Let's try to clean those up.
Here's a list of all these tags. (I would make a SEDE query, but apparently we're not on there yet)
Some of these can easily go (for example, we had 68 until I removed rheumatoid-arthritis), but others are not so clear.
For example, hypervitaminosis is probably not a good choice. A good rule of thumb is whether the tag can be the only tag on a question. Can hypervitaminosis do that? Not really, it's more or less a subset of health.
Another good rule of thumb: Is the tag likely to be used again later? For example, will bivalves ever be used again? Honestly, probably not. And furthermore, even if it's used only a couple times per year, it's pretty easy to create it and retroactively retag applicable questions.
I'll be slowly working on poring through these tags and looking at them, feel free to help. Remember only to edit 3-4 at a time, if applicable, to keep the front page clean. (tag edits bump questions)
If you have any particular tags you feel that need special attention, post an answer to this question describing the tag, what we should do with it and why, and how it's going to be used (with a sample tag wiki).
Note: I'm not trying to say all of these single-question tags are bad, or that they're bad for that reason. However, some of them can definitely go.