Help! Impulse buy on something called a glass eel.

Please don't stuff this into a subforum where it won't get noticed.

I bought a little glass eel today. The problem is, there aren't any thorough explanations as to what it is. The internet offers a few sites dedicated to glass eels, but these sites don't actually tell you if they are freshwater or saltwater. Does anyone know anything about glass eels? Mine was/is in freshwater. Cost $5.00. And it looks like a few of the images that google brings up when I search 'glass eel', but only some. It is not laterally compressed, but looks more like a living spaghetti noodle with a paddle tail.

I hope that's it. I was so afraid it might be one of the saltwater eels in its freshwater/juvenile stage. I'll keep digging and comparing photos for now to be sure it is what I think it is. But it looks more like a worm than an eel. Even the eyes are hard to see.

Oh, good! You know things! So do they really need sand or is a pile of medium gravel going to work?