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Swordfish vs Marlin vs Sailfish: How to Tell the Difference Between the Billfishes

Swordfish vs Marlin vs Sailfish: How to Tell the Difference Between the Billfishes

Written by Scuba.com
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Updated on June 16, 2023
a marlin rising from the ocean waters

Name a big game fish with a long, pointed, spear-like snout. You’d probably say swordfish, or marlin, possibly even sailfish. What is the primary difference between these large distinctive fish — namely the swordfish vs marlin vs sailfish — and how can you tell them apart? Read on to learn the difference between the billfishes!

What are Billfish?

Before we dive into what makes these species of fish different from each other, it’s best to know more about them in general. Billfish are apex predators, hunting smaller fish and cephalopods in deep waters around the globe. They are a migratory species, typically residing in tropical and subtropical waters.

Commonalities between billfishes include a long bill, called a rostrum, which they use for cutting or stunning their prey, and long, narrow bodies. They also have relatively smaller sizes than bony fishes, as well as dorsal fins across a large part of their bodies and thin pelvic fins.

Several billfish species can take a plunge into significant mesopelagic depths, too. Their advanced swim bladders give them this ability, which makes it easy for them to come back to the surface after descending to deep waters.

Swordfish vs Marlin vs Sailfish: How Can You Tell Them Apart?

a swordfish swimming underwater
Image via Shutterstock

A deeper look at the different types of billfish lets us see a lot of differences between them. Take the swordfish vs marlin, for example. While both are members of the billfish family, they are a different species.

The swordfish features a proportionally longer bill than its body, but it doesn’t have pelvic fins. The species also has firm and slightly curved dorsal and pectoral fins, both of which look like a dolphin’s fins. This pelagic hunter’s coloration is blackish brown, fading to slightly lighter shades on the underside.

Swordfish are found throughout the world’s oceans and can withstand the greatest temperature range of all the billfish, possessing a tolerance for both warm and cold waters.

At a glance, marlins, sailfish, and spearfish have two small but discernible differences from the swordfish. First, their dorsal fins run further down the length of their spine, much longer than the swordfish’s shorter fins. Second, their tailfins are narrower. This is where it gets tricky.

What’s the Difference Between Sailfish vs Marlin?

Image via Shutterstock

Sailfish might be the easiest to spot of the bunch, thanks to their prominent and, well, sail-like fin. The dorsal fin of a sailfish is multicolored and very tall, stretching nearly the entire length of the fish’s body. It also has a long upper jaw (sailfish hit and stun large prey with this distinct feature).

Generally a blackish-blue in color, sailfish can actually change shades when they become agitated. They’re also big, with adults reaching up to 10 feet long (three meters) and weighing up to 220 pounds (100 kilos). Young sailfish consume small zooplankton, while adults feed on fairly large bony fish, crustaceans, and squid. They are found in both Atlantic and Pacific waters.

Now, how can you tell a sailfish from a marlin?

There are a number of breeds of marlin: white, striped, blue, and black. Each of these breeds is quite similar in appearance to one another, but the primary difference between these and the sailfish is that distinctive dorsal fin. A marlin’s fins have a typical triangular shape to it, tapering off rapidly along the spine.

Aside from their triangular fins, marlins have elongated bodies and rounded spears (bills). Their bills extend from their snouts. These ocean game fishes can catch and stun cephalopods and fish, such as the fast tuna, with a slash of their bills. Marlins come in the same colors as well, which might make you think that a particular species is the one you’re looking for. But in reality, these fishes vary in appearance.

How Can You Identify the Different Species of Marlins?

To tell the various marlin breeds apart (and from other billfishes), we’ve listed down some of their unique features below.

Blue Marlin

  • A pointed front dorsal fin that’s never as high as the fish’s maximum body depth
  • Flexible pectoral fins, which you can fold back against its body
  • A cobalt-blue back that fades to white; it typically comes with pale blue stripes.
  • A cylindrical body

Black Marlin

  • Has a dorsal fin smaller than its body depth
  • A shorter bill and body compared to other species
  • Dark blue back fading to a silver belly
  • Rigid pectoral fins

White Marlin

  • A rounded dorsal fin that’s usually higher than its body depth
  • Has a lighter, occasionally green color
  • Spots on its belly, dorsal fin, and anal fin

Striped Marlin

  • A possibly taller pointed dorsal fin
  • Visible pale blue stripes that remain even after death
  • Thinner and more compressed body
  • Flexible, pointed pectoral fins

What Makes Spearfish Stand Out from Marlins & Other Billfish?

People often mistake spearfish for marlins since they both have the same colors and body lines. But their dorsal fin has a more gradual taper than marlins. It even has a higher height despite coming at less than 50% of a spearfish’s body height. The dorsal fins on spearfish breeds often feature a bright blue color without any spots on them.

Spearfishes are slender and lightweight with bills that are the shortest of all billfish species. Their actual weight can range from 20 to 60 pounds, but some breeds can weigh at about 100 pounds. You can spot spearfish in most temperate and tropical oceans, as they usually swim along the continental shelf and current lines.

Final Thoughts on Billfish Identification

Image via Shutterstock

When in doubt, check the fins if you get a glimpse of these colorful and beautiful fish. The shape and length of that fin should help you tell the difference between the billfishes when you spot them beneath the sea.

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