It looks like a synbranchid "swamp eel," possibly
Monopterus albus, a wide-ranging Asian species. It has become established in Florida, Hawaii, and Georgia (where it has exhibited some tolerance of freezing conditions). Your friend's finding in New Jersey would be a first for the state, and -- as far as I'm aware -- the northernmost report of this species anywhere in the United States. Probable means of introduction: live food fish or aquarium trade.
I suggest you contact relevant authorities -- I'm not personally familiar with the procedure, but the NAS site I linked may have additional information. Sorry for the rushed post -- I'm in a hurry at the moment.