Members of the Istiophoridae family are characterized by a bill that is rounded; a lateral line retained throughout life; elongate pelvic fins; scales present in the adult; jaws with teeth in the adult; a dorsal fin with a very long base that is sometimes sail-like and is depressible into a groove; 24 vertebrae; and a caudal peduncle in the adult with two keels on each side (Nelson 2006). The members of this family also share many characteristics with the swordfishes, including an elongate premaxillary bill (rostrum) in adults; dorsal fin origin over back of head; pectorals low on body; first dorsal fin lacking true spines, among other traits (see billfish).
Traditional classifications, such as Nelson (2006, 1994), recognize three genera in Istiophoridae: Istiophorus (sailfishes), Tetrapturus (spearfishes), and Makaira (marlins) (Nelson 2006; Agbayani 2008). These taxonomies also recognize the blue and black marlins to comprise the genus Makaira and the white and striped marlins as being part of the spearfish genus of Tetrapturus. However, Collette et al. (2006), utilizing genetic and morphological data, recommend that Istiophoridae be divided into five genera, and this recommendation is followed by the Integrated Taxonomic Information System (ITIS 2008), which recognizes the following five genera: Istiompax (black marlin), Istiophorus (sailfish), Kajikia (white and striped marlins), Makaira (blue marlin, marlins), and Tetrapturus (spearfishes).
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