That's right. He's the King of the Herrings.
So this of course intrigued me, and prompted me to look further in to this species. As it turns out, they don't seem to be related to herrings at all. Best I can tell, the closest taxonomic level they share is that of class, which encompasses every single ray-finned fish. Does the moniker mean that they lord over the herring with their vast size and appetite? Most likely not, as Opah eat mostly squid and krill, and the occasional small fish. Silly old book! Then again, they messed up the species name too, which they don't have much of an excuse for. Lampris guttatus has been called as such since 1788.
Opah are found in tropical and temperate oceans worldwide, and live at depths of between 100 and 400m. Opah are believed to be solitary, and they are not fished for commercially. They are occasionally caught as a byproduct of tuna fishing, and most of the Opah meat sold in the United States is from Hawaii.
There really isn't all that much else known about Opah. There is no indication that their population is threatened or in a decline.