Swordfish ( Xiphias gladius )
|Scientific name of the family|
|Swainson , 1839|
|Scientific name of the genus|
|Linnaeus , 1758|
|Scientific name of the species|
The swordfish ( Xiphias gladius ) is a large, predatory bony fish that can be found worldwide in moderately warm to tropical seas. It lives in the open ocean, comes little near the coast and feeds on other fish and cephalopods .
Its sword-like rostrum , which gives it its name, can reach a third of the body length of adult fish. The scientific name of the species ( Xiphias ) comes from the Greek ξίφος xiphos and means sword . The Latin epithet gladius stands for the Roman short sword ( gladius ). The swordfish is a valued food fish.
The swordfish occurs cosmopolitan at water temperatures between 5 ° C and 27 ° C in all tropical , subtropical and temperate oceans between 61 ° north latitude and 50 ° south latitude. In the western Pacific it lives between 50 ° north and 45 ° south latitude and in the cooler eastern Pacific between 50 ° N and 35 ° S. In the Indian Ocean the distribution area extends north 45 ° south latitude. In the north, the range is limited by the coast of South Asia. In the Atlantic, the swordfish occurs between 50 ° north latitude in the northwest and 60 ° north latitude in the northeast and 45 ° S in the southwest and 45 ° to 50 ° S in the southwest. It is also found in the Mediterranean , Marmara and Black Seas , and occasionally in the North Sea . The genetic exchange between the Atlantic and Mediterranean populations is low.
The swordfish has a spindle-shaped body with a highly oval cross-section. Its sword-like rostrum , which gives it its name, can reach a third of the body length of adult fish. In contrast to the round cross-section of the “spear” of its closest relatives, the sailfish and spearfish (Istiophoridae), the swordfish's “sword” is flattened. It is formed by the elongated upper jaw, in young swordfish the lower jaw is also drawn out to a shorter sword. The sword is already well developed in young fish 10 mm long. In terms of body size and weight, swordfish differ significantly from region to region. The average body length of swordfish caught with longlines in the northwestern Pacific is 1.2 to 1.9 meters. The mean weight of the animals caught in the Mediterranean is between 115 and 160 kg. Fish of the Mediterranean population rarely weigh more than 230 kg, in the western Atlantic they can weigh up to 320 kg and in the southeastern Pacific up to 530 kg. Females grow larger than males, who rarely weigh more than 140 kg. The largest swordfish ever caught measured 4.55 meters with a weight of 650 kilograms.
As they grow, swordfish are subject to major morphological changes. The jaws of adult swordfish are toothless, while young fish with a body length of up to one meter have fine teeth. Young fish are also covered with small, prickly scales, while adult fish from a body length of one meter have no scales. The sideline is absent in adult swordfish, while it is present in juvenile fish up to one meter long.
Adult swordfish have two dorsal fins that are widely separated from each other. The first, much larger dorsal fin is located immediately behind the head and pectoral fins. It is supported by 34 to 49 fin rays; the much smaller second dorsal fin, which is just in front of the caudal fin stalk, has four to six fin rays. Young fish have a longer, continuous dorsal fin. The anal fin is also divided into two parts, the first lies a little behind the middle of the body and has 13 or 14 fin rays, the second, just before the tail fin stalk and a little before the beginning of the second dorsal fin, has three or four fin rays. The pectoral fins are sickle-shaped, relatively rigid and are supported by 16 to 18 fin rays. Ventral fins and the associated pelvic girdle are missing. The caudal fin is large and crescent-shaped, the tail fin stalk of adult animals has a cartilaginous keel on each side. The anus is near the beginning of the first anal fin.
Swordfish are black-brown to bluish-gray on the back, and they get lighter towards the belly. The fin membrane of the first dorsal fin is black-brown, the other fins are black-brown to brown. The eyes are large, the mouth cannot be pushed forward. The gill openings are large, gill rakers are not present. The number of vertebrae is 26, including 15 to 16 trunk and ten to eleven tail vertebrae.
From the at first glance similar marlins , fanfish and spearfish, the swordfish differ in addition to their strongly flattened rostrum by the short first dorsal fin and the lack of teeth, ventral fins and pelvis. In addition, they have only one keel on each side of the tail peduncle; Sailfish and spearfish, on the other hand, have two.
The swordfish has a partially endothermic metabolism . That means: He is able to partially regulate his body temperature from within. The swordfish's eyes and brain are 10 ° C to 15 ° C warmer than the surrounding water. In the outer eye muscle ( musculus rectus superior ), the mitochondria (the "power plants" of the cells) make up 55 to 77% of the cell volume and thus have the highest proportion in all animal cells examined for this characteristic. Furthermore, the myoglobin content in the outer eye muscle is particularly high and the sarcoplasmic reticulum , which stores calcium ions (Ca 2+ ), increases. In contrast, there is a lack of contractile fibrils . The Ca 2+ ions escaping from the sarcoplasmic reticulum are pumped back with ion pumps ( transport proteins ), which leads to the production of heat. The purpose of this warming up of the eyes and the brain is probably to avoid temperature differences and the associated impairment of cerebral and visual performance, which would arise if the prey hunting swordfish swim through water layers of different temperatures. The muscle cells of the rebuilt eye muscle do not have any calcium binding proteins such as troponin or calmodulin , actin and myosin . Here, however, as in other cells, adenosine triphosphate is formed in the mitochondria . When the cell is excited, calcium is released from the endoplasmic reticulum . The increase in calcium concentration promotes the formation of adenosine triphosphate in the mitochondrion. It is used to pump the calcium back into the endoplasmic reticulum with the help of the protein calsequestrin . The work done is converted into heat. There is also a rete mirabile . Through a countercurrent circuit, it causes the heat to be retained in the brain.
Way of life
Swordfish are fish of the open ocean, but sometimes also go to coastal waters. They love warmth and prefer water temperatures above 13 ° C. That is why they are mainly in the epipelagial region above the thermocline between warmer surface water and cold deep water. Their optimum temperature is between 18 ° C and 22 ° C. Of all swordfish species , the temperature tolerance of swordfish is greatest and ranges from 5 ° C to 27 ° C. Swordfish can therefore also dive into the mesopelagial in 5 ° C to 10 ° C cold water at depths of 550 to 650 meters. B. to capture bottom-dwelling fish. They migrate long distances and seek warm waters to reproduce and cold ones to find enough food. In general, they move to temperate or cooler sea regions to forage in summer and migrate to areas near the equator in autumn to winter. Swordfish tagged with transmitters and tracked with satellite telemetry in the northwestern Atlantic Ocean off the coast of Georgia and South Carolina covered between 11 and 1,486.8 km in 30 days, up to 2,547 km in 60 days, and measured the traveled distance after 90 days Distance for the most popular animal 3053.2 km.
Swordfish can reach high speeds. In order to reduce the flow resistance, they have a gland in the head that produces an oily secretion and distributes it over the head via a network of capillaries in the scalp. Lacking their ventral fins, the animals are unable to brake abruptly, and this was unnecessary as there were no obstacles on the high seas before humans began to navigate the seas by ships. Accidents have become known in which swordfish hunting at high speed pierced their swords through wooden boat planks. This can also harm people. On May 31, 2015, a fisherman who went into the water off Hawaii and harpooned a swordfish was downright impaled by it.
As parasites of the internal organs of the Swordfish include monogenea flukes from the subclass (monogenean) digeneans , band - (Cestoda) and nematodes (Nematoda) known. Copepods parasitize on the surface of the skin. The tapeworm Tentacularia coryphaenae was found in the stomachs of all swordfish from the Gulf of Guinea , which had been examined for parasite infestation . Its anus-infecting relative Pelichnibrothrium speciossum was detected in 4.8% of the animals. The prevalence (infestation) for the other parasite species is in between.
Adult swordfish are predatory fish that seek their food in the open water and on the sea floor. They are not picky about it. Above deep sea regions they mainly eat pelagic schooling fish, including tuna , golden mackerel , lance fish , snake mackerel , flying fish , barracudas and others, as well as squids . Across the shallow water areas of the sea, their food spectrum includes mackerel , herrings , sardines , anchovies , lizardfish and garfish . Large swordfish also dive very deep to catch prey in regions where the water temperature is only between 5 ° C and 10 ° C. Here they mainly prey on hake , sea bream , hairtails , mackerel, spiny heads and typical deep-sea fish such as lantern fish , bristle -mouthed fish and deep-sea hatchet . When examining the stomach contents of the cephalopods that have been captured, it can be seen in particular that the swordfish kill their prey by being hit with the side edge of the sword.
Swordfish are very fertile, the ovaries of females can contain 2 to 5 million eggs. The Atlantic population spawns all year round, but mainly from April to September in the Caribbean , the Gulf of Mexico , the Florida coast, and the southern Sargasso Sea . The egg and semen delivery takes place at a depth of 0 to 75 meters and at a water temperature of around 23 ° C. The swordfish of the equatorial Pacific also reproduce all year round, in the central Pacific from March to July, in the western South Pacific from September to December. The best-researched spawning area is in the Mediterranean around southern Italy and around Sicily , especially in the Strait of Messina . With the exception of the winter months of January and February, adult swordfish can be found there all year round; spawning is very intense from June to August. Eggs floating in the open water can be found there from June to September and young swordfish up to a weight of 5 kg from October to December. From November to March, young swordfish are numerous throughout the Mediterranean. The eggs have a diameter of 1.6 to 1.8 mm, the newly hatched larvae are about 4 mm long. The larvae prefer temperatures above 24 ° C. Young fish initially live in the upper water layers and quickly develop into voracious predatory fish. Female swordfish grow faster than males. Swordfish are sexually mature and spawn for the first time by 5 to 6 years of age. It is difficult to determine the age because “annual rings” cannot be read on scales because they are not there and the otoliths are too small. To determine the age, it is therefore necessary to count annual rings on the cross-sections of the fin rays.
The swordfish ( Xiphias gladius ) is the only species of the genus Xiphias and the family Xiphiidae. It represents the sister taxon of the sailfish and spearfish (Istiophoridae) and forms with them the order swordfish-like (Istiophoriformes). Traditionally, the swordfish and the sailfish and spearfish were assigned to the " mackerel-like " (Scombroidei).
Among the mackerel species, however, there seems to be only a closer relationship with the barracudas (Sphyraenidae). Otherwise the swordfish and the other istiophoriformes are probably related to the jackfish (Carangidae) and their close relatives , as well as the Centropomidae , the archer fish (Toxotidae) and the flatfish (Pleuronectiformes). The disc-shaped moonfish (Menidae) are also closely related to the swordfish-like.
The Xiphiidae family has been found in fossil records with certainty since the lower Eocene , 48 million years ago. A much older fossil rostrum, described as Cylindracanthus , is known from the Cretaceous Pierre Shale of South Dakota . It is usually placed in the family Xiphiidae, but shows so few diagnostic features that an assignment to the sturgeon-like (Acipenseriformes) is under discussion.
Xiphiorhynchus from the Eocene and the Oligocene is the first genus that can definitely be assigned to the Xiphiidae. Fossils have been found in Belgium, England, Hungary, Egypt, and the United States. Xiphias itself appeared 15 million years ago in the Middle Miocene , the recent species Xiphias gladius has been recorded since the Lower Pliocene . The extinct species Xiphias delfortrierii , whose fossil remains were found in the Italian province of Pisa ,dates from the same period.
The swordfish is sought after as a popular food fish worldwide. Long lines , harpoons and nets are used for fishing . Because of its size and wildness, it is a coveted trophy for deep sea anglers. When trying to break free from the line, the swordfish engages in a long fight and shoots out of the water in spectacular leaps.
Swordfish meat is pink, extremely tasty and a popular delicacy ; Like tuna , it is firm and very lean. It is marketed fresh or frozen and used for steaks , canned food , sashimi or teriyaki . Adult, large individuals may have accumulated the toxic heavy metal mercury in their flesh in the course of their life .
The main catching nations are Japan , the USA , Italy , Spain , Canada , South Korea , Taiwan , the Philippines and Mexico . Important fishing areas are the Mediterranean Sea, the Gulf of Mexico and in the Atlantic the Georges Bank off the Gulf of Maine , the Grand Bank off Newfoundland , the Gulf of Guinea , and in the South Atlantic the coasts of Brazil and Uruguay . In the Pacific, swordfish are caught mainly from California to Ecuador , Peru and northern Chile , as well as on the east coast of Australia and around New Zealand .
Due to the increased demand, the catch has risen sharply since the 1980s. Between 1950 and 1980 it was below 40,000 tons per year, in 1995 it exceeded 100,000 tons for the first time and, with the last published figures from 2014, reached its peak at 126,879 tons. The IUCN last assessed the total population, with the exception of the Mediterranean population, as not endangered ( Least Concern ) in 2011 . As of 2016, Greenpeace considers the consumption of swordfish meat to be unacceptable, with one exception.
A constellation , a film , several warships of the British Navy ( HMS Swordfish ) and submarines of the US Navy were named after the swordfish , as well as a British biplane , the Fairey Swordfish , which was used as a carrier-based torpedo bomber , reconnaissance aircraft and during the Second World War Submarine hunter was used.
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