At a glance, it’s hard to tell marlin and swordfish apart. Both belong to the billfish family with characteristic long elongated bills extending from their upper jaws.
The two are large marine fishes found in the open waters of the world’s oceans.
Each species is also popular among sports anglers, and some say they taste the same. But they have key differences in appearance, feeding habits, and behavior.
Table of Contents
What Is a Marlin?
Marlin (istiophoridae) is a carnivorous marine fish species with a large long nose, an elongated body, a long dorsal fin, and a spear-like bill.
Its dorsal fin is crescent-shaped, like a sail. Marlins are migratory fish found in all oceans of the world, where sport anglers often hunt them.
There are four types of marlin:
- Blue marlin (makaira nigricans)
- Black marlin (istiompax indica)
- Striped marlin (kajikia audax)
- White marlin (kajikia albida)
Blue marlin has a distinct cobalt blue back and is common in the Atlantic and Pacific oceans. The black marlin has a dark blue back and dwells in the Pacific and Indian oceans.
White marlin is the smallest marlin species found in the Gulf of Mexico, the Caribbean Sea, and Western Mediterranean waters.
The striped marlin lives in the cooler waters of the Indian and Pacific oceans. Anglers are particularly interested in the Atlantic blue marlin, Pacific blue marlin, and white marlin.
What Is a Swordfish?
The swordfish (xiphias gladius) is a predatory and migratory billfish common in the Pacific, Indian, and Atlantic oceans.
These fish have a long pointed beak that they use to hunt prey. Their fast speeds, big bodies, and strength make them one of the most prolific ocean predators.
There is only one species of swordfish, with populations in the Atlantic, Mediterranean, and Pacific.
While the swordfish is nearly at the top of the oceanic food chain, it is still predated upon by giant sharks and whales.
Marlin vs. Swordfish: A Detailed Comparison
The elongated spear-like bill is the most striking similarity between a marlin and a swordfish. Fortunately, the two fish have several differences that help distinguish them.
All marlins have an elongated body with a long dorsal fin that resembles a sail. The marlin’s body is covered with dense, bony scales, while adult swordfish lose all their scales as they mature.
A swordfish has a round body with a triangular-shaped dorsal fin similar to a shark. Compared to the swordfish, the marlin has a brightly colored dorsal fin.
Marlins have a rounded spear-like bill protruding from their snout. Their upper body is either cobalt blue, dark blue (blue-gray), blue-green, or pale blue with stripes.
All marlin species have a paler underbody which is either silver or white.
Swordfish, in contrast, have a deep brown to black back and silver to white underbelly and sides. Unlike marlins, swordfish have flat elongated spear-like bills, almost a third of their body lengths.
Overall, a marlin is larger and heavier than a swordfish. The Pacific black marlin, the largest of the marlin fishes, grows to a length of 15 feet and can weigh as much as 1500 pounds.
Atlantic white marlin are the smallest of the marlin species. They grow up to nine feet in length and weigh about 180 pounds.
Swordfish reach an average of nine to 12 feet and weigh about 1000 pounds at full maturity. Some have the potential to weigh up to 1400 pounds.
Although they are of the billfish family and live in the Indian, Atlantic, and Pacific oceans, these two fish species have different environmental preferences.
Marlin fish prefer the tropical and subtropical waters of the Atlantic, Pacific, and Indian oceans. They swim near the surface of warm water and often migrate to warmer waters.
The swordfish, on the other hand, prefers the temperate and colder parts of these oceans. They will stay near the surface to mid-water depth but have no problem going deeper in search of food. As highly migratory species, they travel from warmer to cooler waters to feed.
Marlins are aggressive predators, which serves them well when hunting down their prey. However, they will often become timid when in the presence of their predators or more aggressive predators.
Marlin fishing techniques take advantage of this trait by disturbing waters where the fish are likely to be found. However, that aggression means marlins put up a fight when captured.
Swordfish are also aggressive and efficient hunters (and equally resistant to being caught). They use their speed and spectacular eyesight to hunt day and night. A swordfish can pursue its prey horizontally and vertically across the ocean.
Diet and Feeding
Marlins feed on small fish and squid, which they hunt in the pelagic ocean. Although their diet consists primarily of mackerels, flying fish, and tunas, they have been recorded hunting dolphins. During their hunting sessions, they can pursue prey to depths of 1,500 ft.
The swordfish feeds mainly on cephalopods and small bony fish. They catch their prey throughout the water column, including the bottom of the ocean. A swordfish will swallow smaller prey whole but slice bigger opponents into smaller pieces before consuming them. The two types of fish use their bills during hunting to stun or slash their target.
Both marlins and swordfish have swim bladders that allow them to seamlessly and effortlessly change depth in the ocean. This feature enables them to hunt more prey and escape anglers.
When comparing marlin vs. swordfish, it’s worth examining their different lifespans. The average marlin can live for 10-15 years, while most swordfish have an average lifespan of 10 years. Female swordfish tend to live longer, with the longest-recorded female swordfish reaching 15. Female marlin fish are also long-lived, with the longest recorded female clocking in 30 years.
The lifespan differences are directly related to the delayed reproductive maturity of swordfish and the predation of juvenile swordfish. Swordfish attain reproductive maturity at four to five years, meaning most don’t live long enough to reach adulthood.
The blue marlin spawns four times annually, depositing eggs for the male to fertilize. Eggs take about one week after spawning to hatch.
Swordfish reproduce through spawning. The timing of the spawning season depends on whether swordfish are in warmer or cooler water. Spawning happens all year round in warmer water and in summer when in cooler waters.
During spawning, the male and female move closer to the ocean surface, where the female releases the eggs. Male swordfish then release sperm to fertilize them. Both marlin and swordfish do not offer parental care to their young ones. Young fish have to fend for themselves after they hatch.
Marlin and swordfish are solitary fish. They hunt alone and spend most of their time swimming alone. However, they form small schools during spawning seasons.
Solitary male and female swordfish tend to pair during the spawning season. You may also find swordfish swimming in loose groups.
Marlin and swordfish are prized among recreational anglers. Fishing, coupled with global warming, has affected them both.
Marlin fishing, especially of the Atlantic blue marlin, has made them a vulnerable species. Increasing ocean temperatures also threaten marlin as it lowers oxygen levels in the water. This phenomenon has seen more marlin fish migrating and staying longer in the cooler northern waters.
Despite the changing climate and sport fishing, swordfish still have a thriving population.
Frequently Asked Questions
Here are the frequently asked questions when comparing marlin vs. swordfish.
How fast are marlin and swordfish?
Marlin and swordfish average about 50 mph. The blue marlin is considered one of the fastest fish, after sailfish, another member of the billfish family. Their speeds make marlin and swordfish prolific hunters in the ocean.
Are marlin and swordfish endangered?
Marlin, particularly the Atlantic blue marlin, are endangered, but the swordfish is considered a low-concern species. Both are subject to recreational fishing, which has resulted in regulating their fishing in different parts of the world.
Why are marlin and swordfish popular choices for recreational fishing?
The size and rarity of marlin and swordfish make them ideal for recreational fishing. Most people who catch them later release them into the ocean, but some will catch them for food.
What animals prey on marlin and swordfish?
Sharks, whales, and humans predate on marlin. Juvenile swordfish are prey to most marine predators, while orcas and other marine mammals predate upon adults.
Do people eat marlin and swordfish?
Marlin and swordfish are popular foods. Pacific swordfish steaks are famous due to their thickness and flavor.
On the other hand, marlin is popular in Japanese cuisine, where it is eaten sashimi style due to the mild flavor of marlin flesh.