As for its ID as a Hybrid eel species can be either a freshwater or marine type of eel, its not how you ID a eel species in a area like this by using a section group area that describes the eel as either marine or freshwater species, and the name Hybrid goes as well with the green moray.
You say now that its 18-20" and is this store owner sure its a juvenile? For if it is a juvenile, its to grow as and its only 18-20" , it should then become not smaller then 3.5' and it could grow larger, what your lacking is its proper ID for you should never buy something you not know what you have and if it be able to have other aquarium inhabitants. For also, if it is still in its juvenile stages, unless one personal dealt with that species or seen a juvenile before, it could be difficult to ID the eel. Also, it could be the spotted moray, if it is I would know its juvenile appearances. I did thought that you were going to upload a few photo shots and be sure to have a close up of the neck and head from either side.
So if it is a juvenile eel, its color patterns will appear differently from one stage of the eel from its juvenile to adult stages. besides, i known of lfs that sold a giant moray as a snowflake eel, lol
From a very small part were you say green color appearances it could be a juvenile green moray also their happens to be a yellow golden moray that is also called as golden moray, and it would be solid yellow with a few dark markings just pass its head, near around to its gills, but a picture would say it all, you are making a long mystery out of this for after that you speak of spots like a tess, but also it could be the spotted moray eel, for it happens to be loaded with spots, and it too is a very aggressive species.
Buddy
