Here’s what I know, but the info is from ten years ago. The eel in question, Anguilla sp. is known to breed in the Sargasso Sea in the southwestern Atlantic. We know this because we find lots of larvae swimming around the Atlantic, and if you plot the gradient, they come from there. No one has ever (at least 10yrs ago) found an adult eel swimming their way TO the SS to mate. But obviously, they must. This lifestyle: adulthood in fresh water, breeding in the sea has a name which escapes me at the moment (college bio was even more then ten yrs ago). It is the opposite of what Salmon do, obviously.
The adult eels are found in rivers in North America and Europe. They seem to be two distinct species; at least, genetically, the succeeding generations in both continents seem to have come from the preceeding generation, and not a mix. But both larvae spread out from the SS.
This species is quite fascinating, and commercially important, too, at least in Europe. At one time, this fish was a dietary mainstay in parts of England, that I know of, and probably other places as well.
As far as the IO and Pacific, I’m not sure. Either there are no members of this genus in those oceans, or they have their own equivalent of the SS in which they mate. Sorry, that’s all I know off the top of my head.