I think i can help out abit here
Now you say it is from a stream, so basically classed a fresh water eel you have there...
So common knowledge says they are along the same lines as catfish you find in lakes and rivers, also known as parasite fish, because they carry illnesses and such, but if you got this one from a fresh water strean, good chance you are in the blue
They will eat meat and veggies, if it has teeth protruding from its mouth, the advisable approach would be to feed it mainly meat, however suppliment its diet with some veggies, best thing to do first, is to test its eating habits, because from what i know, what eel's eat first in life, they tend to persue the rest of their lives, so test him out by offering him different food's and seeing what he takes first...
Also bewarned, freshwater eel's arent too different from Marine one, because they do grow to large sizesSo he might out grow your tank, depending on the type of eel you have, but most eels would outgrow their tank...
All really i can advise when it comes to parasite fish, is to test them out, any signs of illness and such, i would advise getting rid of the fish, and another thing, hopefully you only have the eel in that tank, and no other occupants, because it might feed off any occupants it might have in the tank with it...