A large [grouper] native to the tropical Atlantic and Gulf of Mexico.
The earliest source we know of for the name of the species is from the Oxford English Dictionary, which quotes from a book published in 1697, entitled A New Voyage [Round the World], by the famed explorer, William [Dampier].
In the book, Dampier logs his expedition to Jamaica, where he encounters Jews (who are an extreme minority, as they are in most other nations), who favor a certain type of fish - the [jewfish] - which they consider to be the grandest kosher fish.
Kosher, because it has both fins and scales, and the grandest, because it is by far the largest kosher fish around, as it is in the Floridas Keys (second to only the shark, when including all fishes). The quote from the [OED] is: The Jew-fish is a very good Fish, and [I judge] so called by the English, because it hath Scales and Fins, therefore a clean Fish, according to the Levitical Law.