Re: OOC
Oh. the bone issue.
Bones are not impurities, they're part of the critter. Also, they can be food items. Birds are cooked whole, generally, and bird or beast, portioned bits are frequently bone it. Bones can be boiled down for stock, and bone marrow, if you eat that sort of thing, is generally cooked in bone.
So, no, a Purify spell wouldn't remove (native) bones from fish, or anything else. You'd need a Butchery of Food preparation spell for that.
Now, if the animal has poison glands, the contents WOULD be removed. The spell specifies poison, same as it does disease.