Yes, of coures what I write has to be substanciated. Symptoms of liver failure in fishes takes some year to develop, and by then, it may be incurable. You are right that the mollies have plenty of fatty acids which are harmful. In fact if you ask me, feeding mollies gives your eel little nutrition, equal to throwing in chunks of fat for the eel to eat. Even though mollies can survive in brackish and marine water, they do lack the specific diatery requirements of marine organisms, trace elements suck as iodine etc. I highly discourage you from using mollies as a primary food source, however if you insist on giving your eel mollies, the best thing would to feed the eels on that sparingly, say once a month? Squid is still the best staple food for eels.