These two fish live in similar environments, eat similar diets, but are different sizes and have differently shaped bodies. Below, readers can explore a few more similarities and differences between these two fish. 

Swordfish (left) vs Marlin (right) Visual Comparison

Credit: PicomyIsland.org (left), Jackiemora01 (right)


Main Differences Between a Swordfish and Marlin

Here are the top five main differences/similarities between a swordfish and marlin: 

  • Appearance: Both fish have long pointed bills. Swordfish ar more round than marlin in their bodies, which are longer and narrower.
  • Size: Both fish grow up to 14 feet, and up to 1,400 pounds.
  • Diet: Both swordfish and marlin have similar diets: smaller fish and squid. They use their long pointed bills to slash at prey.
  • Dorsal fin: The dorsal fin on swordfish is similar to that of a shark, whereas marlin have a more crest-shaped fin. Marlin tend to have more colorful dorsal fins too, being more blue-ish.
  • Habitat: Swordfish are known to migrate lots, living at depths of ~500 metres. Marlins live in deep tropical oceans, and migrate less than swordfish,

We’ll explore these differences and interesting facts about each fish more below.

Swordfish 

Swordfish are also sometimes referred to as broadbills. They are the only members of the family Xiphiidae and are closely related to marlins, but they are not the same animals. It is named after the shape of its bill, which looks like a sword. 

Swordfish on the deck of a ship
Swordfish on the deck of a ship


Appearance 

Swordfish are recognizable animals. They, like marlins, have long, pointed bills that they use for slashing and hunting prey. They are also popular fish among sport fishermen. 

Swordfish have long bodies that are slightly more rounded than marlins. They start out with scales and teeth, all of which they lose by the time they are fully grown adults. The fish grow to a maximum of fourteen feet in length (but most only reach around ten feet) and can weigh up to around 1,400 pounds, very similar to the size and weight of marlins.

Marlin and swordfish also have different dorsal fins. The latter is more similar to a shark. It is less crest-shaped than a marlin’s is. It’s possible to determine the age of a swordfish by the growth rings found around their fins. 

The skeleton of a swordfish
The skeleton of a swordfish

Credit: GFDL


Habitat 

These animals are highly migratory, meaning that they do not stay in one region of the ocean for their entire lives. Generally, they are found around depths of 550 meters, or 1,800 feet. There have been instances in which these fish have been seen as deep as 2,234 meters or around 7,300 feet. 

Swordfish have an interesting organ around their eyes that heats their brains and eyes. This helps their vision, allowing them to swim in deeper, colder, and darker waters. These fish swim alone most of their lives or in loose groups of other swordfish. Often, it’s possible to find them around the surface, a sight that many fishermen and boaters seek out and praise as extraordinarily beautiful. They have also been known to breach, jumping out of the water. This is a practice seen in some sharks and whales and is generally thought to be used to dislodge parasites and other pests. 

Diet 

Swordfish, like marlins, feed on a variety of prey. This includes fish and squid. They can use their long bills to slash at and stun prey. But, despite popular depictions, they don’t use their bills to stab prey as one might with a sword. 

Facts about Swordfish 

  • They have an organ around their eyes that heats their brain and eyes. 
  • Marlin and swordfish have different dorsal fins.
  • They don’t use their bills to stab prey.
  • They are also popular fish among sport fishermen. 
  • Swordfish have been known to breach. 
  • They are the only members of the family Xiphiidae. 


Marlin

Marlins is a fish from the family Istiophoridae, which includes around ten species. They are closely related to the swordfish, but they are not the same species or in the same family. (Swordfish are the only members of the family Xiphiidae). 

Interestingly, marlins are some of the fast species in the ocean. They can reach around 100km/h (or 68 mph) for short periods. This allows them to get away from most predators easily. It has also made them a prized fish for fishermen. 

Appearance 

Marlins are easy to recognize due to their long bodies and sharp, spear-like snouts, sometimes referred to as bills. This is also referred to as “rostrum.” It is used to slash and stun prey that they are in pursuit of. It also gives the fish a striking and dangerous-looking profile. They have a stiff dorsal fin the runs along their backs and is often defined as “crest-like.” 

Marlin on a fishing line
Marlin on a fishing line

The largest species of marlin can grow to be around 16 feet long and weigh around 1,400 pounds. The fish are usually between white, grey, and blue in color with a darker stripe along their upperside. They are large fish, popular with sport fishermen. A few species, such as the Atlantic blue marlin and White marlin, are endangered due to overfishing. 

Habitat 

Marlins are found in tropical deep-sea oceans around the world. But most commonly in the Pacific, Atlantic, and Indian Oceans. 

Marlins live between twenty and thirty years, with females generally being long-lived.

Diet 

Generally, marlins feed on squid and small fish in the pelagic region of the ocean, including tunas, mackerels, and flying fish, as noted by NC DEQ. They also have been known to hunt dolphins. 

The marlin, like the swordfish, has a swim bladder. This allows the fish to change depths quickly without using a great deal of energy. This is helpful when in the pursuit of prey. They can reach depths of up to 1,500 feet during the day, something that makes fishing for these fish more challenging. 

Facts about Marlins 

  • The marlin was the fish featured in Ernest Hemingway’s The Old Man and the Sea. 
  • The speed and size of these fish is often over exaggerated. 
  • Two species of marlin are endangered. 
  • Marlin are some of the fastest marine animals. 
  • They can weigh close to 1,500 pounds. 
  • The marlin can change depths quickly due to its swim bladder. 


FAQs  

Are a swordfish and a marlin the same thing?

No, swordfish and marlin are two different types of fish. They share many distinct similarities, though, including their general profile, habitat, and diet. 

What is a predator to a swordfish?

Predators of adult swordfish include orcas, sharks, dolphins, tunas, and more. They are also at threat from human beings and climate change. 

Are swordfish and marlin carnivores?

Yes, swordfish are carnivores. They eat many different different types of fish as well as squid and octopus. 

What is a swordfish’s favorite prey?

Swordfish like to eat everything from fish to squid and octopus. They specifically enjoy bluefish, mackerel, and hake. Herring is also a part of their diet. 

Is marlin fishing illegal? 

There are some countries that do not prohibit commercial fishing of marlin, but in most places, it is extremely limited. This is due to the fact that some species are endangered. The sale of marlin meat is banned in the United States, for example.