Marlin fish is a common name for large marine fish in the family Serranidae of the order Perciformes. The maxilla of this fish family protrudes forward like a spear head, its side beak is blunt and round, its body is covered with small angular scales, and its skin is thick as leather. Widely distributed in the upper waters within 200 meters in tropical and subtropical regions. This fish is native to tropical and temperate waters of the Atlantic, Pacific, and Indian Oceans, and is the most well-known among all fish species. The fish mentioned in Hemingway's "The Old Man and the Sea" is also the largest fish caught by the San Diego Old Man, and is referred to as the marlin in the novel.

The formal name is "Blue Spearfish", which is a large marine swordfish with a spear shaped mouth. It is a species of tropical and subtropical oceanic upper water bodies, fierce in nature, agile in swimming, and carnivorous. Marlins prefer places with higher surface temperatures, feed on mackerel and tuna, and also dive deep to eat squid. They are famous for their ability to lift huge striking objects that they hook onto, and this rare ocean monster is the holy grail for sports loving fishermen. People consider their meat as a delicacy, especially in Japan where it is often used as a raw material for sashimi.