Blue marlins are blue-black above and silvery white below, with about 15 rows of pale cobalt-colored stripes along the flanks. The 1st dorsal fin is plain blackish or dark blue and the other fins are brown black with a tinge of dark blue in some specimens. The anal fin bases have a tinge of silvery white. Lateral line is a network of interconnecting canals (Smith 1997).

Blue marlin of the Indo-Pacific and the Atlantic are conspecifics now both known under the name of Makaira nigricans. The Indo-Pacific blue marlin was previously known as M. mazara (Collette et al. 2011c, IOTC 2011b). It is a pan-tropical species occurring in the Atlantic, Pacific and Indian Oceans mainly between 35┬░ N and 35┬░ S latitude (Fischer and Bianchi 1984, Nakamura 1985).

WC, EC, KZN, MOZ Known throughout the Indian Ocean north of 30°S latitude, but sometimes reaching as far south as Cape Town (Heemstra and Heemstra 2004).

Blue marlin undertakes extensive and seasonal migrations with fish migrating into higher latitudes during the summer months and returning to equatorial waters during winter (Rivas 1975, Nakamura 1985, Cyr et al. 1990, van der Elst 1993).

Blue marlins are apex predators that feed on a diversity of epipelagic fishes, especially smaller tunas and squids (Heemstra and Heemstra 2004).

Blue marlins are heterosexual, dimorphic species and females growing considerably larger than males (Rivas 1975, Namakura 1985, Cyr et al. 1990, Hopper 1990). They spawn from summer to autumn in the southern latitudes < 30┬░S in the Indian Ocean (Leis et al. 1987, Hopper 1990, van der Elst 1993) but may spawn year-round in equatorial waters < 10┬░S (Kailola et al. 1993). There are distinct breeding populations between 30┬░N and 30┬░S. Specific spawning grounds have yet to be identified in the Indian Ocean (van der Elst 1993). Age at 50% maturity for combined sexes is 1-2 years (Prince 1991; Heemstra and Heemstra 2004) and length at 50% maturity for males is ~140cm EFL and for females is ~200cm EFL (Heemstra and Heemstra 2004).

Offshore (>30m)