There are three kinds of large pelagic fish in the sea, all of which look alike. They are characterized by a long arrow on their heads, which is actually an extension of their jaws. These three kinds of fish are swordfish, marlin and swordfish.

In fact, these three kinds of fish belong to three families and genera. They are different kinds of fish.

Sailfish can be easily distinguished from the other two kinds of fish because it has a long dorsal fin. 1 The picture shows saury.

The second picture is marlin and the third picture is swordfish.

In Hemingway's novel The Old Man and the Sea, the old man caught a marlin.

Sailfish and marlin are difficult to distinguish from each other in appearance. Swordfish swords are generally long, and they are real bone swords, with thick middle and thin sides.

Marlin's arrow is short, and its cross section is round, like a slingshot.

Figure 4 shows the skull of swordfish on the left and marlin on the right. You can clearly see the difference in appearance between the two kinds of fish.

Figure 4. Swordfish's bone density is relatively small and the middle is porous, because it is often damaged and easy to repair.