I read that they go from brackish to fresh. The one I have is in fresh now but I'm curious how I can make the perfect environment for him. Any suggestions?

Can you give us specifics on this fish? I tried a google search...all I know is it's an eel. :laugh:

If it's a freshwater moray eel...then I'd recommend a few teaspoons of salt per gallon. Or no salt at all...what ever he seems happy in. :)