Sailfish

Sailfish are billfishes, members of the taxonomic suborder Xiphiodei. Billfishes include swordfish Xiphias, black and blue marlins Makaira, and spearfishes and white and striped marlins Tetrapturus. Until recently, sailfish were classified as two species, Indo-Pacific sailfish, Istiophorus platypterus, and Atlantic sailfish, Istiophorus albicans, but genetic studies show that they are all one species, Istiophorus platypterus.

Billfishes are named for a prolongation of the upper jaw into a rostrum, or bill, that resembles a sword (flat in cross section) or a spear (round in cross section). They use the bill primarily to attack prey. Billfish are apex predators, feeding mainly on schooling fishes such as sardines, anchovies, mackerel, and jacks. Being at the top of their ocean food chain, billfish don't have regular predators, but they are occasionally eaten, particularly in their juvenile stages, by other large fishes such as tunas, wahoo, and dolphinfishes.

The "sail" in the name sailfish refers to the prominent first dorsal fin, which is taller than the fish’s greatest body depth. The sail folds along the top of the fish and can open up in an instant. Sailfish often pop their sails while feeding, perhaps to startle their prey.

Off the Yucatán Peninsula in the Gulf of Mexico, sailfish feed on "bait balls" during the winter and spring months. They work cooperatively to corral prey fish such as sardines into tight schooling balls, then dart in and out of the balls, using their bills to slice the masses into smaller, more manageable pieces. They swat or bat their bills from side to side in order to stun their prey, feeding on the fish until they're all gone.

Bibliography
Holland, Jennifer S. "In the Whirl." National Geographic (September 2008), 70-79.

Collette, Bruce B., Jan R. McDowell, and John E. Graves. "Phylogeny of Recent Billfishes (Xiphioidei)." Bulletin of Marine Science. Vol. 79, no. 3 (2006), 455-68.

Nakamura, Izumi. FAO Species Catalogue: Vol. 5. Billfishes of the World. United Nations Development Program, Food and Agriculture Organization of the United Nations, 1985.

Levine, Charlie. "Return to Isla: Good Fishing and Quiet Living Make Isla Mujeres a Top Sailfish Destination." Marlin (April 10, 2008).

Tinsley, Jim Bob. The Sailfish: Swashbuckler of the Open Seas. University of Florida Press, 1964.

Moyle, Peter. Fish: An Enthusiast's Guide. University of California Press, 1993.

Bone, Q., N. B. Marshall, and J. H. S. Blaxter. Biology of Fishes, second edition. Blackie Academic and Professional, 1995.

Reebs, Stéphan. Fish Behavior in the Aquarium and in the Wild. Cornell University Press, 2001.

Other Resources
Guy Harvey Research Institute. Oceanographic Center, Nova Southeastern University, Florida.

The Billfish Foundation.

Marlin magazine.

Keen M International Sport Fishing.

Sailfish Color Changes

Sailfish can appear in a startling array of colors, from subdued browns and grays to vibrant purples and even silver. Their body colors are often highlighted by stripes of iridescent blue and silver dots. Sailfish can change their colors almost instantly, since the change is controlled by their nervous system. Nerves send signals to specialized cells called chromatophores and iridophores, which are found mainly in the skin's dermis layer. Chromatophores are irregularly shaped cells (branched cells with a central core) that contain pigment, and there are several kinds, including melanophores, which contain the black or brown pigment melanin. Below the melanophores lie iridophores, which produce color structurally rather than with pigment. These cells have layers of guanine crystals that reflect light; wavelengths of light bouncing off them interfere with each other, creating iridescent colors such as metallic blue and silver. The sailfish appear dark when the pigment inside the melanophores is evenly distributed across the cells. But the fish can draw pigment from the melanophores' branches into their core, allowing light to hit the iridophores below and the iridescent colors to flash through.

Bibliography
Farrant, Penelope. Color in Nature: A Visual and Scientific Exploration. Blandford, 1999.

Moyle, Peter, and Joseph Cech, Jr. Fishes: An Introduction to Ichthyology, 5th ed. Pearson, Prentice Hall, 2004.

Smith, J. L. B., and others. Smiths's Sea Fishes, revised ed. Struik, 2003.

Last updated: August 7, 2008