Blue Marlin are a member of the family Istiophoridae. They possess a long, pointed bill and a non-rigid pectoral fin that can be folded against the body. The back of the fish is cobalt-blue in colour, breaking into silvery white on the lower half of the body. About 15 pale blue bars can be seen along the body, which fade after death. They feed on squid and finfish, particularly tuna-like species.
Blue Marlin can reach a maximum length of 5 m. Females can weigh more than 900 kg, while males only reach a weight of around 170 kg.
Blue Marlin are pelagic fish, but rarely found in ocean waters less than 100 m deep. Compared to other marlins, Blue Marlin have the most tropical distribution. They can be found throughout eastern and western Australian waters and depending on warm ocean currents, as far south as Tasmania.
Blue Marlin are distinguished from Black Marlin (Makaira indica) by the non-rigid pectoral fin and the presence of blue bars displayed along the body. The lower dorsal fin height of Blue Marlin distinguishes it from Striped Marlin (Tetrapturus audax), whose dorsal fin height is equal to its body depth.
Recreational fishing for this species is centred over the continental slope. Blue Marlin are frequently caught using lures, however many have been taken drifting with live baits off the New South Wales coast.