Sailfish (Istiophorus platypterus) are four to five foot long fish living in the Atlantic Ocean. They are blue in color and have a characteristic sail on top of them, stretching the entire length of their back. They frequently can attain speeds of 50 knots. Description: color dark blue on top, brown-blue laterally, silvery white underbelly; upper jaw elongated in form of spear; first dorsal greatly enlarged in the form of a sail, with many black spots, its front squared off, highest at its midpoint; pelvic fins very narrow, reaching almost to the anus; body covered with embedded scales, blunt at end; lateral line curved above pectoral, then straight to base of tail.

Similar Fish: white marlin, Tetrapterus albidus; young blue marlin, Makaira nigricans (spectacular sail-like dorsal of sailfish is most notable difference).

Where found: OFFSHORE species, in south Florida associated with waters near the Gulf Stream; off the Panhandle near the 100 foot fathom line.

Size: common to 7 feet.

• Florida Record: 116 lbs.

Remarks: rapid growing species, reaching 4 to 5 feet in a single year; swims at speeds up to 50 knots; feeds on the surface or at mid-depths on smaller pelagic fishes and squid. They are the fastest fish in the ocean,

Source

• http://marinefisheries.org/FishID/billsail.html
• http://marinefisheries.org/FishID/billsail.html (added on part)