Marlin and Swordfish: Do they belong to the same family?

Power, beauty, strength speed, all adjectives that describe any of the 11 species of Marlin. They are the embodiment of a true sportfish. On the other hand, we have the just as powerful, just as alluring, mysterious and mystifying Swordfish. On the surface, the average joe would say these fish are closely related and a part of the same family of fish, but to the seasoned angler, these two popular game fish couldn't be anymore different. 

For episodes on Sailfish or Marlin, go to our Youtube Channel at

For episodes on Sailfish or Marlin, go to our Youtube Channel at

Billfish, such as Marlin and Sailfish, are pelagic gamefish that are known to feed towards the surface of the water column and are found in all tropical and subtropical oceans. Of course, billfish are characterized by their prominent pointed bills, which are smooth and round throughout. They use this tool to slash and stun prey while feeding on anything from schools of bait fish, to small tunas and mahi mahi. They will also feast upon the occasional crustacean or cephalopod. 

Swordfish are predatory marine animals that are found in tropical or temperate oceans. They are also known as "Broadbills", because unlike Marlin, their bills are flat and shaped like a sword, hence the name. Similar to the Marlin, these fish can grow over 14 feet long, but their bodies tend to have differing shapes. A Marlin's body is long and tubular throughout, while the Swordfish's is more elongated and rounded. The bill of a Swordfish is also much longer than a typical Marlin's, being 1/3 of their total body length. The pec fins and dorsal fins of a Swordfish are also more similar to that of sharks, such as the Mako, than that of Marlins.

So the question arises, are these two fish part of the same Family of billfish?

There are 12 species of billfish that are subdivided into two separate families. 11 species, including Marlins, Spearfishes and Sailfish, belong to the family Istiphoridae, while the Xiphiidae family, contains only one family, the Swordfish Xiphias Gladius. 


Swordfish are deep sea fish that can are found anywhere from the surface of the ocean, down to depths of over 2,000 feet. Fish over 200 pounds are normally females, and reach sexual maturity when 5 or 6 years old. The long bill of the Swordfish allows it to slice at its prey,  as opposed to spearing it like their distant cousins.  These fish are extremely fast and are know to strike prey are up to 50 miles per hour. Their diet consists of small fishes such as rockfish and the barracuda, but squid and crustaceans also make up a big part of their diet. Swordfish are able to hunt at such deep depths due to their ability to heat their eyes. Research has shown that heated retinas in the eyes work up to 10 times more effectively than cool temperature eyes by allowing them to capture and process low levels of light more quickly.

As you can see, Swordfish and Marlins are both extremely sought after billfish, but are also very different and are in fact, not closely related. To learn more about Swordfish, and how to fish for them, check out the Into the Blue Episode Below.

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