Pacific 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 dolphin fishes.
Sailfishes grow quickly, reaching 1.2-1.5 m (4-5 ft) in length in a
single year, and feed on the surface or at mid-depths on smaller
pelagic fishes and squid. Individuals have been clocked at speeds of up
to 110 km/h (68 mph), which is the highest speed reliably reported in a
fish. Generally, sailfish do not grow to more than 3 m (10 ft) in length
and rarely weigh over 90 kg (200 lb), although larger specimens have
been seen off the shores of Central America. Pacific sailfish are quite
a bit larger than Atlantic sailfish. The current world record for
Pacific sailfish is 221 lbs and the Atlantic sailfish is 141 lbs.
The sail is normally kept folded down and to the side when swimming, but
it may be raised when the sailfish feels threatened or excited, making
the fish appear much larger than it actually is. This tactic has also
been observed during feeding, when a group of sailfish use their sails to
"herd" a school of fish or squid.
Sailfish Color Changes
Both Atlantic and Pacific 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:
Schultz, Heidi, National Geographic Magazine, Sept. 8, 2008 & Aug. 13, 2008
Wikipedia
International Gamefish Association
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