Swordfish

The swordfish is named due to its characteristic elongated snout resembling a sword. It is mainly found in the warm tropical or temperate oceans like the Atlantic, Indian, and Pacific oceans. The sword is mainly used as a weapon against both predators and prey. They are different from other snouted fishes like marlin or spear-nosed since the sword is flat. Marlins have a more rounded snout. 

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The swordfish fish does not have any teeth or pelvic fin. They can grow to a maximum length of 15 feet (4.6 meters) and weigh around 1000 pounds (450 kilograms). The body is bluish or purplish above and silvery below. They can be found near the surface of the water. However, they can dive to a depth of 2234 meters. Typically, they are found at a depth of 550 meters. They belong to the family Xiphiidae. The scientific name of Swordfish is Xiphias gladius.

General Description of Swordfish

Swordfish are also called game fish or broadbills in other countries. The International Game Fish Association has an all-tackle angling record of a swordfish caught that weighed 536 kilograms. The Pacific swordfish are larger in size than the Mediterranean or the Atlantic swordfish. Females are found to be larger than males. 

Most swordfish attain biological maturity at the age of 4-5 years. The average lifespan of swordfish is a minimum of 9 years. The record for the oldest swordfish is 12 years for males and 16 years for females. The age of a swordfish can be determined by counting the annual rings on their fin rays. Their otoliths cannot be considered for calculating age since they are very small in size. 

Just like sharks, swordfish are also ectothermic. They also have specialized organs located next to their eyes to supply heat to their eyes and brains. Such heating of the eye helps to improve vision in water. An improved vision is required to catch their prey effectively. Their body temperature is measured around 10 to 15°C  more than the surrounding water temperature. They belong to the rare group of marine fishes, along with tuna, marlin, and few shark species, that can conserve their body heat. 

Feeding and Movement of Swordfishes

Most people believe that the sword of a swordfish is used as a spear. However, such beliefs are misleading. Most swordfish use their nose to slash their prey so that they become an easier catch. However, research is going on its use as a spear against larger animals like sharks.

The major weapons of swordfish to catch their prey are their agility and great speed. They are considered to be amongst the fastest fish in the marine ecosystem. They do not exhibit any schooling behavior. Most swordfish tend to live alone or in small groups. Even in small groups, they tend to be far away from each other (at least a 10-meter gap between two swordfish).

Most swordfish come to the surface for basking. Boaters often see their first dorsal fin above the water's surface and consider it a beautiful sight. However, swordfish are most famous for their jumping abilities. The jumping of a swordfish is also called breaching. They often breach to dislodge any pest like lampreys and remoras from their bodies.

Swordfish exhibits the widest tolerance of water temperature amongst the billfishes. They generally prefer a temperature range of 18 to 22 °C. Swordfish also exhibit migratory properties. They prefer to migrate to colder climates during the summer for feeding. They feed every day, mostly at night. They come near the surface of the water to feed on smaller fishes. They prefer to stay at deeper levels during the day. 

Adult swordfishes feed on a variety of pelagic fishes like silver hake, mackerel, Barracudas, herring, rockfish, and lanternfish. They also take in squids, crustaceans, and demersal fishes.  Adult swordfish use their sword for larger prey, while the smaller ones are swallowed as a whole.

Threats to Swordfish

Although swordfish exhibit exclusive predatory activities, they also face several threats. There are almost 50 parasite species associated with the swordfish. Some of them are discussed above. There are other invertebrates like roundworm, tapeworm, and copepods. Scientists have compared the parasites list of swordfish of Mediterranean and Atlantic origin. They concluded that some of these parasites, like Anisakis spp., can be used as a  biological marker for the existence of the Mediterranean variety.

Along with the parasites, the swordfish also face threats from bigger natural predators. Killer whales are documented to prey on swordfish. They also have fallen prey to the shortfin mako. The shortfin mako is a shark species that are extremely fast swimmers. Juvenile swordfishes run a higher risk of predation than adults. 

Intensive fishery is also a major threat to the swordfish. As a result of such activities, the sharks and the swordfish have lesser prey to catch, and therefore, go into intense competition. Many swordfishes also get caught up in the fishing nets.   

Breeding of Swordfish Fish

If you ever visit the North Pacific ocean in the summer or spring, you will know that that is the perfect breeding condition for swordfishes. Batch spawning takes place in warmer water at a temperature of more than 24 °C. The equatorial Pacific region provides such conducive conditions all year round. Swordfish generally spawn in the Sargasso Sea in the North Atlantic. They also spawn from November to February near South Brazil in the southern Atlantic ocean. 

The females carry the eggs that hatch to give birth to the new ones. Larger females can carry more eggs than smaller females. They can carry millions of eggs at a time. Embryonic development starts around 2.5 days after fertilization. The larvae mainly live near the surface and have a unique look. They start developing the bill when they reach around 1 cm in length. 

Swordfish Fishing

Before the advent of longline fishing, the swordfish did not face much risk. However, after its introduction into the market, swordfish faced increasing risks. Although there are no cases of swordfish attacking humans, there are cases where they have destroyed boats.

Most people also catch swordfish for recreational fishing. The abolition of longline fishing along the coasts has a positive influence on the swordfish population. During recreational fishing, the most commonly used fishing technique is the deep drop technique. This technique is used to catch swordfish from the deeper layers of water during the day. However, fishermen target the upper layers at night.

The standard baits used for fishing swordfishes are herrings, whole mackerel, bonito, mullets, and squids. Some fishermen also use glow lights or battery-operated lights to attract swordfish to the bait. It is important for the fishermen to use strong fishing rods and large reels since the swordfishes are generally very heavy. 

Swordfish as Food

Swordfish is also widely regarded as food. They are considered to be oily fish with lots of essential nutrients. Some of these nutrients include Proteins, Vitamin D, Potassium, Magnesium, Selenium, etc. Swordfish-based foods have been predicted to have profound effects as medicinal values against several diseases. Some of them are:

• May Lower the Risk of Developing Heart Diseases

The major reasons for most heart diseases are high cholesterol levels and high blood pressure. Swordfish meat has omega-3 fatty acids that can positively influence both cholesterol levels and blood pressure. Moreover, such effects do not interfere with the ongoing medication. 

It also has DHA and EPA, which can treat tachycardia, lower blood pressure, and improves the elasticity and function of the blood vessels. They can also help to lower blood triglycerides and remove blood clots from arteries. Vitamin D also helps in lowering blood pressure.

• May Lower the Risk of Cancer Development

Vitamin D, omega-3, and selenium are the major components of swordfish meat that can have anticancer effects on the body. Vitamin D and omega-3 have anti-inflammatory properties. Inflammation is a hallmark of several cancers. Both these components were found to be effective in conferring protection against colorectal cancer. They might prevent cancerous cells from dividing and can promote their death. Vitamin D can also prevent blood vessels from supplying blood and nutrients to these cells.

Omega-3 creates major blocks in the process of metastasis. Metastasis is a vital part of any cancer progression. Several studies in human and animal models also suggest that omega-3 can reduce the size of colorectal tumors.

Cancer progression largely involves the generation of oxidative stress. Selenium is a powerful antioxidant that triggers the cellular antioxidant system. Selenium can have a protective influence against breasts, prostate, lungs, and liver cancer.

However, it is important to note that individual components of swordfish meat demonstrate the anticancer effects. The effects of this meat on different cancers are still yet to be elucidated.

• Can Promote Bone Health 

The primary function of Vitamin D in our body is the stimulation of calcium absorption in the gut. This helps in bone formation. Vitamin D deficiency in our body has been linked to several forms of bone loss, fractures, and elevated risk of falling. Selenium also promotes bone health by preventing osteoclasts from breaking the bones. Since both selenium and vitamin D are essential components of swordfish meat, intake of such meat might positively influence bone health.

Conclusion

Swordfish are marine predatory and migratory fishes that are characterized by the long sword-like nose. The sword is flat, which distinguishes it from marlins and other snouted fishes. Swordfishes use this sword to slash prey. They are extremely fast swimmers. The presence of specialized heating organs near the eyes of the swordfish helps them in visualizing prey. They are extremely heavy and long and prefer to live solitarily or in small groups. Swordfish is mainly hunted as an oily fish with several nutritional values.