Marlins are often mistaken for swordfish and, even though both species are billfish, there are several differences in their appearance. Both have long spear-like bills, but marlins have more elongated bodies and smaller pectoral fins than swordfish. In addition, there is a long, rigid fin located on its back which forms a crest near the fish’s crown. Its name is believed to have originated from the resemblance it bears to a sailor’s marlinspike, and the species belongs to the largest order of vertebrates (perciform).

There are several different types of marlin including white, black and striped. The blue marlin is one of the most popular, and authors Zane Grey and Ernest Hemmingway wrote extensively about their blue marlin fishing experiences. Preferring to remain in a tropical climate throughout the year, they are found in the waters of the Atlantic, Pacific and Indian Oceans and are one of the biggest fish in the world. Spending most of its time in deep ocean waters, the fish feeds mainly on smaller species that travel in schools such as tuna and mackerel. They stun or kill their prey, using their bill, by diving repeatedly through the school and then return to eat them after the others swim away. The jaws and the roof of their mouths are covered in small, sharp teeth which assist when they are chewing.

Blue Marlins are extremely fast swimmers, being able to reach speeds of 80km/hr. They are also able to rapidly change colour, using pigments within their body and light-reflecting skin cells. Even though they are normally a silvery blue colour, they can appear anywhere between silver and black. The thick, bony elongated scales that their bodies are covered with will sometimes help add to this illusion.

In most marlin, the female can grow up to four times larger than the male reaching a maximum length of 5m and weighing up to 815kg. Their bill is about 20% of the length of their body. Their body’s high fat content means that they are considered highly prized game fish, due to their popularity in certain markets. One example of this is their use Japan to make sashimi. Many of the fish also get caught in tuna nets, and the blue marlin was recently added to Greenpeace International’s seafood red list.

The marlin can be home to many parasites, including flukes and tapeworms, and infestations can affect its feeding patterns. Even though they have few natural predators apart from large pelagic sharks, such as the great white, the blue marlin has also been added to the list of endangered species due to the fact that it’s been the world’s greatest game fish since the 1920s.