Not one sailfin blenny, but two
In Reef Fish Identification: Florida, Caribbean, Bahamas, Paul Humann says sailfin blennies (Emblemaria pandionis) are "occasional" in Florida, the Bahamas and the Caribbean. The photo by Laurie Cullenward, Madison, WI, of two, not just one, sailfin blennies in the Caymans confirms Humann's added note that they "can be locally abundant."
Click here for a close up of a sailfin blenny's amazing territorial display.