SWORDFISH: CHARACTERISTICS, HABITAT, RESPIRATION, REPRODUCTION - BIOLOGY - 2025

The swordfish (Xiphias gladius) is a marine species that is part of the Xiphiidae family. Its main characteristic is its long and flattened beak, shaped like a sword. This is formed by the fusion and extension of the bones that make up the jaw.

Contrary to popular belief, the sharp beak is not used to attack prey, but to stun it. This species could use it to ram a school of fish, and then consume those that are injured or disturbed. It has also been attributed a defensive use, as protection against its natural predators.

Swordfish. Source: MathKnight

Other relevant aspects are the presence of a large first dorsal fin and the absence of pelvic fins. In addition, it does not have teeth and its skin lacks scales. Their body is elongated and they measure approximately 4 meters. The record for fishing for this species was caught in Chile in 1953. This specimen weighed 536.15 kilograms.

This species is ectothermic, so it does not have the ability to regulate its internal temperature. This is why it has special organs next to the eyes, which heat the brain and eyeballs, thus improving their vision.

Conservation

In some regions, such as the Mediterranean, the swordfish population is declining. However, in general this species is stable. This is why the IUCN has categorized the Xiphias gladius as of least concern for extinction.

However, the international protectionist organization indicates that, if actions are not taken to help solve the problems that afflict it, it could be seriously threatened.

Threats

Swordfish are threatened by hunting them, either accidentally, for sporting purposes or for food. It is a species sensitive to overfishing, since, among other things, the young are captured, preventing the species from recovering from overexploitation.

Marketing of meat

Regarding the use of its meat, it is highly valued in the market, because it is compact and aromatic. In addition to this, it is highly nutritious, as it contains vitamins and minerals.

Among other benefits is its low caloric level, occupying the seventh position among the most nutritious fish, with only 110 Kilocalories. Likewise, the liver of this fish is used in the pharmaceutical industry, due to the large amount of vitamin A it has.

Harpoons, fishing nets, driftnets and longlines are used to catch it. The use of these constitutes in turn a danger for sharks, birds and sea turtles. This is because they get caught in the nets and die.

Hunting

In general, the capture of this species is incidental, since it becomes entangled in the lines of longline hooks, used in the tuna fishery.

Regarding recreational and sport fishing, these are practiced mainly off the coasts of Ecuador, California, Peru and the north of Chile.

characteristics

Swordfish skeleton. Postdlf

Physiology

Swordfish is an ectothermic animal, since it does not have the ability to maintain, in a constant way, the internal temperature. This will depend on the conditions of the water where you live. However, they have special organs on both sides of the eyes, which contribute to the regulation of temperature.

These warm the brain and the eyes, being able to raise their temperatures from 10 ° C to 15 ° C above that of the water where it lives. Keeping the eyes warm helps improve their vision, making it easier for them to chase and catch their prey.

The fact that both organic structures can maintain their higher temperature outside, allows the swordfish to explore wider thermal niches. Likewise, it can hunt in deep and cold waters.

On the other hand, like the rest of the large pelagic animals, the anatomy of the Xiphias gladius is specialized for fast swimming. However, this fish has a low percentage of white muscle, which allows it to make a sudden start. As an adult, it could swim at 25 meters per second.

Peak

The most relevant characteristic of swordfish is the elongation of its upper jaw. Thus it is flattened, pointed and sharp, similar to a sword. Its size is almost a third of the total length of the animal.

Due to this particularity, this fish is known as the gladiator. However, its beak is not used as a spear to catch fish. Thus, it is not used to impale prey, but to hurt or hit large ones.

Also, it can ram schools of fish, stunning them to facilitate catching. Likewise, the researchers point out that swordfish may use its beak as protection, against threats from its natural predators.

In this sense, there have been clashes between this fish and the short-finned shark (Isurus oxyrinchus), where it is attacked in the stomach, causing its death.

Body

Its body is robust and has an elongated cylindrical shape. The spinal column is made up of 26 vertebrae, 15 pre-caudal and 11 caudal. Likewise, it is slightly flattened on the sides, deeper in the posterior part of the gill openings and finer in the caudal part.

At birth, this species has a body covered in scales, however, they tend to lose them progressively. Once an adult, they are completely lacking.

Fins

This species has two dorsal fins that, in the juvenile stage, are continuously arranged. When they reach adulthood, these structures are separated, the first being larger than the second. Thus, the first dorsal, which originates from the gill openings, has between 34 and 49 rays and the second dorsal, 4 to 6 rays.

In addition, the two anal fins it has are distant from each other and one is larger than the other. The first anal fin has between 13 and 14 rays and the other has 3 or 4 rays. The second anal fin is positioned slightly further forward than the second dorsal fin. The anus is located near the origin of these two fins.

As for the pectoral fins they are somewhat stiff, long and narrow. They have between 16 and 18 rays and are located in the lower part of the body. The tail fin is short but very wide and has a crescent shape.

Likewise, it has a caudal peduncle, with a prominent keel on each side and a cut on the ventral and dorsal surface. On the other hand, this fish lacks ventral fins.

Color

The upper part of the body can vary between blackish brown, violet, dark blue and even black tones. These dark colors fade until they reach the ventral area, which can be whitish, with flashes of silver. As for the fins, they can be brown or dark brown.

Head

In relation to this, the long lamellae and the high laminar frequencies increase the gill resistance to the passage of water through this structure, thus speeding up the ventilation of the ram.

The bifurcation of the gill filaments could increase the surface area of ​​the gills, much more than other members of its class. This could allow swordfish to access oxygen-poor waters, such as those found deep in the oceans.

Likewise, the fact that the lamellae are long and low in height, allows a greater number of them to exist in the gill cavity. In addition, the branchial openings are wide and the membranes present in these structures are only basally attached.

Reproduction

The data related to the size and biological age that allows swordfish to reproduce are varied, including, in some cases, they could be contradictory. However, their sexual maturity could occur between 2 and 4 years, and may vary depending on the area where they live.

Being an oviparous animal, its reproduction is by means of eggs. In this species, they are characterized by being pelagic and by their small size. Thus, they could measure between 1.6 and 1.8 millimeters in diameter. It should be noted that the female of Xiphias gladius could store up to 29 million eggs.

The mode of fertilization is external. In this process, the females expel into the water, in several successive layings, millions of eggs. At the same time, the males swim around them. Both continue to swim near the fertilized eggs, to scare off predators that try to eat them.

Spawning is conditioned by environmental factors, mainly by surface temperature. Thus, those who live in the Atlantic do so in waters with temperatures between 23 and 26 ° C. While those who live in the northeast of the Atlantic do so throughout the year.

Larvae

After two days of being fertilized, the embryo has developed, giving way to a larva of approximately 4 millimeters. This usually lives, during the day, near the surface, but at night it could move to a greater depth, reaching even 30 meters.

At this stage, the body is almost not pigmented. As the larvae grows, the body becomes thinner and when it measures around 10 millimeters it already feeds on other larvae.

Being 12 millimeters long, the beak begins to develop, both parts being the same size. As it grows, the top of the bill grows faster than the bottom.

In relation to the dorsal fin, the first of these develops after the appearance of the beak. When the fish is 23 centimeters, this structure already extends throughout the body. The second fin develops when the marine animal is approximately 50 to 52 centimeters tall.

Swordfish hatchlings have a different appearance than the adult. Thus, they only have a very long anal and dorsal fin. In addition, the tail is rounded and both jaws are elongated and serrated. With respect to the skin, it has scales and rough plates.

Feeding

Swordfish are opportunistic feeders, characterized by seeking their food in all depths of the ocean. Thus, it can hunt both on the surface and at the bottom of the sea.

The larvae feed on zooplankton, including the larvae of other fish. In the juvenile stage, they eat squid, pelagic crustaceans, and fish.

Once adult, their diet includes a wide range of fish. In deep water, they catch pelagic fish, including tuna (Thunnus), flying fish (Exocoetidae), dolphins (Coryphaena), Alepisaurus, barracudas (Sphyraenidae), Gempylus, and pelagic squid (Ommastrephes, Loligo, and Illex).

Also, when this species swims in shallow water, it tends to feed on neritic pelagic fish, such as mackerel, anchovies, herring, sardines, marlin, saurians, silver hake, mackerel, barracudas, and lanternfish. In addition, they catch demersal species, crustaceans and squid.

The dams may vary, according to the geographical location and their availability. Thus, in the Northwest Atlantic, 82% of swordfish eat squid and 53% eat fish, including bluefish.

The hunt

The Xiphias gladius generally, during the day, descends to deep water, between 500 and 2878 meters, to feed. On the contrary, at night they rise to the surface or areas close to them, to feed on pelagic species

The works on how to eat describe various techniques. Among these, the swordfish rises between a group of fish and hits them with its beak. Then turn and gobble the dead or injured fish.

Small prey are eaten whole, while larger ones are usually cut with their beak. Likewise, research indicates that the vast majority of large prey, such as squid and cuttlefish, have cuts on their body. In contrast, small prey are eaten whole.

Behavior

Adult swordfish generally have solitary behaviors, until now it has been unknown that they form schools in open areas of the ocean. However, in the Mediterranean, it has been sighted forming groups. This action of staying together could be associated with the search for food.

However, during the spawning season, this species becomes gregarious, forming schools of various fish.

They usually swim alone or in loose aggregations, up to 10 meters apart between each fish. Often, it may rest on the surface of the water, where its large dorsal fin is displayed.

Also, they have been seen making powerful jumps out of the water, thus becoming a great spectacle for sailors who are nearby. This behavior could be associated with the need to eliminate parasites that lodge in their skin, among which are worms and copepods.

In addition, with these movements off the surface, the swordfish could try to shake off remoras and lampreys that often cling to it.

Migration

Swordfish, like other pelagic species, undertake a vertical migration. One of the reasons for these displacements is the water temperature, associated with the seasons. Also, the availability of food is an influencing factor in said migratory behavior.

This species is primarily a warm-water fish. Their movements towards other latitudes occur, in the summer, towards cold or temperate regions, in order to feed. During the fall, it returns to the warm waters, to spawn and hibernate.

The specialists propose two theories, related to the migration in waters of the Northwest Atlantic of swordfish. The first suggests that, in summer, this animal moves east and north, along the entire continental shelf. In the fall, return to the west and south.

The second approach suggests that some groups travel in the summer from deep waters to the continental shelf. When autumn arrives, it returns to the deep regions of the Atlantic.

References

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