The name actually comes from anti-semitic origins. It isn't at all offensive to Jews, they in essence named the fish.
"But by far the greatest source we have about our fishy friend 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 Florida's 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."