Not sure how closely related they are, not in the same family anyway. There's a few species called glass catfish, but I think Kryptopterus vitreolus is the most common one. Shadow catfish are Bagridae, while glass catifsh are Siluridae. Both need similar water parameters and are midwater fish. The glass catfish though can get as much as an inch bigger and also has translucent skin so you can see all the bones and organs...and yeah I just realized you knew that since you saw them for sale.