Swordfish

The swordfish is a large ocean fish known for the long, flat, sword-shaped bill that sticks out from its upper jaw. It lives in warm and cool waters in every ocean on Earth. Its scientific name is Xiphias gladius, which comes from Greek and Latin words that both mean "sword." A full-grown swordfish can reach 15 feet long, counting the bill, and weigh more than 1,000 pounds. That is about as heavy as a grand piano.

The bill is the swordfish's most famous feature. It is made of hard bone and can be nearly one-third of the fish's total length. Scientists once thought swordfish used the bill like a spear to stab prey. They now know the fish usually slashes it sideways instead. One hard swipe can slice a school of smaller fish into easier meals. The swordfish then circles back and eats the pieces.

Swordfish are built for speed. Their bodies are smooth and shaped like a torpedo. Adults have no scales and no teeth. Their tails are stiff and curved like a crescent moon, which pushes them through the water with hardly any drag. Scientists have measured swordfish swimming at around 50 miles per hour, making them one of the fastest fish in the ocean.

They are also deep divers. A swordfish can plunge more than 2,000 feet below the surface, into water so dark that humans need submarines to see down there. To hunt in that darkness, the swordfish has one of the biggest eyes of any fish. Each eye is about the size of a baseball. A special muscle behind the eyes and brain acts like a tiny heater, keeping them warm in the freezing deep.

Swordfish mostly hunt alone. They eat squid, mackerel, herring, and other fast-moving fish. Baby swordfish are tiny and fragile. They drift near the surface and have rough, scaly skin and small teeth, which they lose as they grow up.

Adult swordfish have few natural predators. The main ones are large sharks, such as mako and great white sharks, and killer whales. People fish for swordfish too. Swordfish steaks are popular in many countries, and commercial fishing fleets catch them with long fishing lines that stretch for miles. Some populations were overfished in the 1990s. Careful rules and catch limits have helped numbers bounce back in parts of the Atlantic, though scientists still watch them closely.