Blue Marlin Fish

Body elongated and not very compressed; upper jaw produced into a robust but not very long beak; two dorsal fins, the height of the first less then the greatest body depth, short anteriorly, taller in the middle, then becoming shorter posteriorly; pectoral fins falcate and flexible, with 21 to 23 rays; body densely covered with small, embedded scales with 1 or 2 sharp points; back dark blue, with 15 bluish bars across the flanks; belly pale silver; membrane of first dorsal fin blue black, with dark spots (Ref. 55763). Dark blue above, silvery white below; sometimes with light blue vertical stripes; 1st dorsal fin blackish to dark blue, other fins dark brown with tinges of dark blue in some specimens. Body blue-black dorsally and silvery white ventrally, with about 25 pale, cobalt-colored stripes, each consisting of round dots or narrow bars (may not always be visible especially in preserved specimens). Bill long, extremely stout and round in cross section. Nape conspicuously elevated. Right and left branchiostegal membranes completely united together, but free from isthmus. No gill rakers. Body densely covered with elongate, thick, bony scales, each often with 1 or 2, sometimes 3, posterior points. Caudal peduncle with strong double keels on each side and a shallow notch on both the dorsal and ventral surfaces.

Spawning probably takes place year-round in equatorial waters to 10° latitude (although 1 study has suggested this needs verification) and during summer periods in both hemispheres to 30° latitude, in both the Indian and Pacific oceans (Ref. 6390).In the southern hemisphere, concentrations of spawning fish probably occur around French Polynesia (Ref. 30354).

Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.

Dorsal soft rays (total): 40 - 45; Analsoft rays: 18 - 24; Vertebrae: 24

Acoustic tagging studies (Ref. 4683) suggest that blue marlin primarily inhabit the surface mixed layer, which is the relatively uniform layer of water between the surface and the top of the thermocline where water temperatures start to drop suddenly (Ref. 6390). Studies have also suggested that fish spend more time close to the surface at night than during the day (Ref. 6390).In the Pacific Ocean, blue marlin concentrate year-round in tropical waters, but a part of the population undertakes large seasonal movements away from equatorial waters to about 30°S (Ref. 30354). These movements, mostly undertaken by males of 35-75 kg (Ref. 30354), occur as waves in the northern and southern hemisphere summers (Ref. 6390). Fish moving into eastern Australian waters in the summertime are probably part of 1 of these migrations (Ref. 6390).Blue marlin also live year-round in the Eastern Indian Ocean between northwestern Australia, Java and the Lesser Sunda Islands, with maximum concentration during the Northwest Monsoon (November to April), and between the equator and 13°S during the Southeast Monsoon (April to October) (Ref. 6390).Known to feed in and near surface waters, but sometimes take food in relatively deep waters as is shown by the presence of deep-dwelling squirrel fish (Holocentrus laeteoguttatus) in the stomachs of this species in Hawaii.

Epipelagic and oceanic species mostly confined to the waters on the warmer side of the 24°C surface isotherm and known to effect seasonal north-south migrations. Not usually seen close to land masses or islands, unless there is a deep drop-off of the shelf. Remain mostly within the upper 37 m. Believed to form small-scale schools of at most 10 individuals. Larger fish tend to swim solitarily (Ref. 43) but smaller ones form schools of about 10 individuals (Ref. 9987). Feed on squids, tuna-like fishes, crustaceans and cephalopods (Ref. 9308). Also caught with troll lines (Ref. 9308). The flesh is of good quality and is marketed frozen and prepared as sashimi and sausages in Japan (Ref. 9308); also utilized fresh (Ref. 9987). Also Ref. 9692.

fisheries: commercial; gamefish: yes