Just tested the bite rate on this using Meatballs. After 100 catches (not including mobs and Arrowwood Logs) I caught 96 Dark Bass, and 4 Duskcrawler. 4% bite rate.
Of course, results may vary, so let's call it an even 5%.
Ok, watch how I, a veteran angler, will actually help you distinguish between dark bass and duskcrawlers when your angler's sense doesn't kick in.
It's simple, assuming you are high lv fishing or you're capped on the skill, duskcrawlers will put up minimal fight when you hook them. How? you will at least see one directional arrow indicating the fish is fighting, whereas dark bass will put up NO fight at all. This way you can let go of the fish that put up no fight and hook and land the ones that do. This will save you the time you take dealing with dark bass in general terms.