this is my first post on the freshwater side of this site but i think this is something you guys would know better. my question is, can the freshwater moray eels that ive seen in petstores tolerate brackish, and even marine conditions? i have only eyer seen them in freshwater in petstores, but my local fish store guy said he has heard of people gradually raising the specific gravity of a species only tank with one of them in it, and so long as the acclimation is slow, it can go from freshwater to full blown marine life? anyone have any knowledge on this topic?

I have no knowlege on FW moray eels specifically but I know there are many species acclimated to a variety of water conditions. As an example..some of my shrimp come from a natural habitat with a PH just above 5, and they're acclimated up to 6.8, and even beyond that (up to 7.5) in my tanks. There's always risk involved and not all of them make it, I'm guessing it wouldn't be that different with Eels, although i've heard many species simply will or will not tolerate living out of their specific -gravity-, as you mentioned. They may live for some time but gravity, and not old age will be the cause of death. Like I said though, I don't know if your eels are quite as sensitive as some species may be.