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The swordfish (Xiphias gladius), also known as the broadbill, or the forktail, is the only species in the bony fish family Xiphiidae. The swordfish is highly prized as a food fish, and as a game fish. Its most distinguishing characteristic is the remarkable elongation of the upper jaw, which resembles a long, flattened, serrated sword and can extend up to one-third of the body length. The sword is used as an offensive weapon, and to spear prey, which may be other fish or large mollusks. Swordfish often attack schools of mackerel, gashing several fish with their sword before devouring them.

Swordfish are dark in color, most often brownish black or black, with a lighter brown below. Adult swordfish are devoid of scales and of teeth. Commercially, swordfish are caught by harpooning, and fish in excess of 1,200 lb (545 kg) have been taken by this method. Swordfish are spotted by their curved dorsal fin exposed above the water surface. Swordfish are also caught by rod-and-reel using heavy tackle, and are baited by trolling squid or mackerel. When hooked, a swordfish will make extreme efforts to free itself by leaping out of the water several times before eventually tiring. The angler may have to patiently play the fish for three or four hours before it is subdued. The record catch for a swordfish by rod-and-reel is 1,182 lb (537 kg).

When injured or hooked, a swordfish may thrust itself out of the water, squirm violently and attack anyone or anything in its path. When approached by a boat, the fish may pretend to be exhausted and then suddenly ram its sword into the side of the boat. The force of the thrust can be sufficient to pierce a 2-in (5 cm) thick, solidwood side of a boat. If the boat hull is wooden, the sword may go in too deep to be removed by the fish, and may be broken off in order to escape.

The sail fish (Istiophorus spp.), spearfish (Tetrapturus spp.), and marlin (Makaira spp.) are relatives of the swordfish, but are placed in the family Istiophoridae.

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