The Gladiators of the Ocean
Xiphias gladius, otherwise known as the swordfish, is the only species of the Xiphiidae family. Often regarded as prized food and game fish, the swordfish is not currently an endangered species, however its population is declining. Around 2014, it was being overfished. Overfishing caused swordfish numbers to decline considerably since the 1980s and the population was 70% lower than what was considered sustainable (Oceana, conservation charity). However, as of 2019, the US has seen a decline in the total annual catch of swordfish, and it is no longer considered to be overfished.
As a meal, it provides an excellent source of selenium, a micronutrient that offers important cancer-fighting and heart health benefits. It is considered protein-rich and loaded with niacin which:
- Lowers LDL cholesterol (bad cholesterol), is used to treat high cholesterol which can otherwise have negative impacts on the heart.
- Increases HDL cholesterol (good cholesterol).
- May reduce symptoms of Arthritis, and may help prevent heart disease.
It also contains vitamin B12, zinc and Omega-3.
In spite of its name, the sword-looking bill extending from the swordfish's snout is not used to spear, but instead may be used to injure its prey by slashing at it, thus weakening it and making it an easier catch. Although its bill is significantly elongated, the swordfish relies on its speed and agility in the water in order to catch its prey.
The sword is flat, broad, and more rounded in comparison to its similar-looking species from the Istiophoridae family. Hence, it is often referred to as the broadbill.
It is a scale-less fish and has a tall dorsal fin (the little arc protruding from its spine in the photo). It is also identified by its lack of pelvic fins and of teeth. As seen in the image, it is often purplish or bluish for the upper half of its body, and silvery nearer to its stomach and lower half. On average, it grows to a maximum length of 4.6 metres, and a maximum weight of 450 kilograms.
They prefer water temperatures between 18 and 22 degrees Celsius (64 and 72 degrees Fahrenheit), but have the widest range of tolerance among billfish, and can be found anywhere from 5 degrees to 27 degrees Celsius (41 to 81 degrees Fahrenheit). During summer, they typically migrate towards colder regions to feed. They eat daily, often at night, when they rise to the surface in search of smaller fish. During the day, however, they often stalk the depths of the oceans, settling at 550m below surface level, and have been recorded as deep as 2,878m before.
Unfortunately, they lose all teeth and scales by adulthood. Adult swordfish feed on a range of pelagic fish; mackerel, barracudas, silver hake, rockfish, herring and lanternfishes, but they can also eat squid and crustaceans.
The female swordfish tend to be larger than the male swordfish. They are external bearers; meaning fertilization of the egg occurs externally. Female swordfish carry 1 to 29 million eggs which are all fertilised externally and float to the surface. The eggs are usually 1.8mm long. They do not care for their babies and lack maternal instincts, so as soon as the eggs hatch, the new swordfish are an easy target and may be killed by nearby predators, but most manage to escape and begin growth. They live an average of 9 years.