Indo-Pacific sailfish, Istiophorus platypterus
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Sailfish is the common name for any of the large marine fish comprising the genus Istiophorus in the Istiophoridae family of the Perciformes order, characterized by a dorsal fin that is very long, sail shaped, and taller than body depth and by an elongated bill resembling that of the swordfish and other billfish.
Sailfish play an important role in marine food chains, largely as apex predators consuming and helping to balance populations of squid, octopuses, and bony fish such as sardines, anchovies, dolphins, mackerel, and tuna. While they are very fast swimmers, sailfish, and particularly young sailfish, find themselves prey of dolphinfish and sharks, among other predators. For humans, sailfish are highly prized game fish, known for their incredible jumps. Their unique form and behavior, including herding small prey and using their bills to stun and maim larger prey, adds to the wonder of nature.
There are two extant species of sailfishes, the Atlantic sailfish (Istiophorus albicans), common to the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico, and the Indo-Pacific sailfish (Istiophorus platypterus), native to the Indian and Pacific Oceans. However, some authors consider these to be the same species, Istiophorus platypterus, known variously as the Atlantic sailfish, Indo-Pacific sailfish, or just sailfish. It was originally classified in the same genus as the swordfish, as Xiphias platypterus (Gardieff 2008).
Sailfish commonly are placed as are part of the suborder Scombroidei. The suborder includes species that likely are the fastest swimming fish in the world, including bluefin tuna, swordfish, and sailfish (Nelson 1994, 424). Other members of the suborder include barracudas, mackerels, and snake mackerels. Members of the suborder are characterized by an upper jaw that is not protrusible (not highly mobile) and by having the premaxilla (cranial bones forming the front, central upper jaw) fixed (an adaptation to feeding on larger prey) (Nelson 1994, 424).
The various billfishes (sailfishes, swordfish, marlins, and spearfishes) are generally separated into two families, the Xiphiidae and Istiophoridae, with the swordfish (Xiphias gladius) the only extant member of Xiphiidae, and the other billfishes placed within three genera within Istiophoridae (Nelson 2006; Agbayani 2008a). The three genera placed in Istiophoridae are Istiophorus (sailfishes), Tetrapturus (spearfishes), and Makaira (marlins) (Nelson 1994; ITIS 2004). However, some recent taxonomies have suggested that five genera be recognized within Istiophoridae (Collette et al. 2006).
In some classifications, sailfishes are placed together with the swordfish, marlins, and spearfishes in the family Xiphiidae (Nelson 1994). That is, all the fish known as billfishes are placed together in this one family, with four extant genera with 12 species in the family. Nelson (1994) follows this procedure because "there is abundant evidence that the formerly recognized Xiphiidae and Istiophoridae are sister groups" and that as terminal groups in Scombroidei they should be placed in the same family. As a comprehensive billfish family, Nelson (1994) characterizes Xiphiidae by adults having an elongate, premaxillary bill (or rostum), as well as an inferior mouth, the dorsal fin beginning over the back of the head, and the dorsal fin lacking any true spines and from 37 to 55 rays (Nelson 1994, 428). The billfishes also lack finlets behind the dorsal and anal fins, have two anal rays, the pectoral fins are inserted low on the body, the pelvic fins are reduced (one spine and two rays or absent), and the gill membranes are free from the isthmus (Nelson 1994, 428). Similarly, Collette et al. (2006) and some recent taxonomies, while recognizing the families Istiophoridae and Xiphiidae, place these two familes together under their own subfamily Xiphioidei, rather than Scombroidei.
Istiophoridae, which Nelson (1994) lists as the subfamily Istiophorinae, is characterized by a rounded bill, elongate pelvic fins, scales (the swordfish in family Xiphiidae lacks scales in adult), jaws with teeth (the swordfish lacks teeth in the adult), a lateral line throughout life, and 24 vertebrae (the swordfish has 26 vertebrae) (Nelson 1994, 428). Most prominent of the Istiophoridae is the dorsal fin, which has a very long base, which is sail-like in some species, and is depressible into groove (Nelson 1994, 428).
A notable characteristic of the billfishes is the remarkable ability to practice a form of endothermy, a type of warm-bloodedness where an elevated body temperature is maintained through internal means. Billfish exhibit a type of endothermy known as cranial endothermy whereby only the brain and eyes are warmed (Nelson 1994; Block et al. 1993). They remain "cold-blooded" (specifically poikilothermic) in that they do not maintain constant internal temperatures and the temperature often mirrors the ambient temperature. But by being able to raise the temperature of their brains and eyes, they can have faster eye movements when hunting, which is valued when diving deep into the ocean where the water is very cold.
What distinguishes the sailfish from other members of the family (subfamily in case of Nelson 1994) is the shape of its dorsal fin and pelvic fin. The first dorsal fin is sail shaped and distinctly higher than the body depth and the rays of the pelvic fin are very long (Nelson 1994, 429). 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.
As with other members of the family, the sailfish uses its elongate premaxillary bill to stun fish by slashing back and forth (Nelson 1994, 428).
Both species of sailfishes grow quickly, reaching 1.2 to 1.5 meters (four to five feet) in length in a single year. Generally, sailfish do not grow to more than three meters (ten ft) in length and rarely weigh over 90 kilograms (200 pounds), although larger specimens have been reported. They are one of the smaller members of the Istiophoridae family (Gardieff 2008).
The body color of sailfish varies depending on level of excitement, but overall is dark blue dorsally and white with brown spots ventrally (Gardieff 2008). There are about 20 bars, consisting of light blue dots, on each side of the fish, and the fins are generally blackish blue, with the anal fin base white (Gardieff 2008).
Although swimming speeds of fish in water are hard to measure, some consider the sailfish the fastest fish in the ocean. In speed trials carried out at Long Key Fishing Camp in Florida, one sailfish was measured at 68 miles per hour (110 kilometers per hour), based on taking out 100 yards of line in three seconds (Martin 2008). This is the highest speed reliably reported in a fish. However, the fish was leaping while its speed was timed, so it does not completely represent swimming speed.
Sailfish typically feed on the surface or at mid-depths on smaller pelagic fishes and squid. Their diet also includes faster fish like tuna and mackerel, made possible because of their own fast swimming speed, at least for short distances.
While commonly two species of sailfish are recognized, Istiophorus albicans and I. playpterus (Nelson 1994; Agbayani 2008a, 2008b; ITIS 2008b, 2008c), some authors recognize a single worldwide species, I. platypterus (Gardieff 2008; ITIS 2008a; Collette et al. 2006; Agbayani 2008b). Utilized below are I. albicans for the Atlantic sailfish and I. platypterus for the Indo-Pacific sailfish.
The Atlantic sailfish, Istiophorus albicans, is found in the Atlantic Oceans and the Caribbean Sea, except for large areas of the central North Atlantic and the central South Atlantic, from the surface to depths of 200 meters (656 feet). Basically, it is found from about 50° N to 32° S in the eastern Atlantic Ocean and from about 40° N to 40° S in the western Atlantic Ocean, with an aggregation off the coast of West Africa in the eastern Atlantic Ocean and its highest abundance in the western Atlantic Ocean found in the Gulf of Mexico, the Caribbean Sea, and Florida's Atlantic coast (Gardieff 2008). It has been found in the Mediterranean Sea as well, although there are few records for this area (Gardieff 2008).
The maximum length is up to 3.15 meters (124 inches), and the International Game Fish Association (IGFA) lists the record weight as 128 pounds (58.1 kilograms) (Gardieff 2008). Fish in southern Florida tend to be smaller, generally between 1.73 and 2.29 meters (68 to 80 inches) (Gardieff 2008).
The Indo-Pacific sailfish, Istiophorus platypterus, is native to the Indian and Pacific Oceans. Widely distributed in tropical and temperate regions, it is found from 35° N to 35° S in the eastern Pacific and from 45-50° N to 35° S in the western Pacific, as well as in the Indian Ocean to about 35-45° S latitude (Gardieff 2008). It is found in abundant numbers off Papua New Guinea and the Philippines, as well as off Hawaii and from Tahiti to the Marquesas (Gardieff 2008).
The maximum size for sailfish in waters of the Pacific Ocean is recorded at 3.4 meters (134 inches) in length, and 100 kilograms (220 pounds) in weight (Gardieff 2008).
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