I wonder what the differences are between these and Mastacembelus frenatus. They look incredibly similar.
Edit: Actually, after looking at the photos of each species on Fishbase.org, I'm wondering if there's some misidentification going on, on the hobby side. The "M. frenatus" (aka starry night eels) that I've seen over the years don't really look anything like the specimen that Fishbase displays as M. frenatus. They look very much like OP's fish, which more closely resembles Fishbase's Mastacembelus cryptacanthus specimen (but the pattern on Fishbase's M. cryptacanthus is also quite different from OP's fish, though maybe that's just down to regional variation or something?).