White marlin are a species of billfish found in the Atlantic Ocean. They get their name from their stark white bellies that fade into a dark blue dorsal fin and upper body. White marlin are often misidentified as roundscale spearfish, or vice versa, as they look essentially identical. They both have a uniquely shaped dorsal fin that has a rounded top, unlike the standard pointed dorsal fin of other billfish. This is often referred to as a “hatchet” dorsal fin. They have streamlined bodies that allow them to swim quickly and continuously over hundreds of miles.