Keeljaw Needlefish, Tylosurus acus melanotus
The Keeljaw Needlefish, Tylosurus acus melanotus, whose common Spanish name is marao isleño, is a species in the Needlefish or Belonidae Family, known collectively as agujónes in Mexico. It is also known as the Agujón Needlefish and was once thought to be the Pacific equivalent of the Atlantic Agujón, Tylosurus acus, a species only found in the Atlantic and lacking the keeljaw. Some of my scientific friends believe that this is form of the Pacific Agujón, Tylosurus pacificus, but others recognize it as a separate species. Globally, there are six species in the genus Tylosurus, three of which are found in Mexican waters, two in both the Atlantic and the Pacific and one in just the Pacific.
The Keeljaw Needlefish have slender elongated rounded bodies with a dark blue upper body, silvery sides, and a white belly. They also have a light blue stripe along their flanks. Their jaws are prolonged and their upper and lower beaks are of equal length, relatively long (18-20% of standard length), slender, and up-curved with many long pointed teeth. The key to identification is a keel found near the tip of their lower beak (pictured below). Their caudal fin is deeply forked with the lower lobe being much longer than the upper lobe. Their dorsal fin has a long base while their pectoral and pelvic fins are short.
The Keeljaw Needlefish are an oceanic pelagic fish found in the first 30 feet of the water column. They reach a maximum length of 1.0 meter (3 feet 3 inches). They are a very rare and poorly studied species and very little is known about their behavioral patterns.
In Mexican waters the Keeljaw Needlefish were thought to be found only around the various oceanic islands including Clipperton, Cocos, Malpelo, Revillagigedos, and Tres Marias, however, I have made catches in the coastal waters in the greater Los Cabos area, including within the Sea of Cortez, extending the known range for this species.
The Keeljaw Needlefish is easy to identify due to the keel under its chin and therefore cannot be confused with any other species, but it is otherwise very similar in appearance to the Houndfish, Tylosurus crocodilus and the Pacific Agujón, Tylosurus pacificus. There is some controversy about this species in the scientific fish community, with some believing that it is a standalone species and others believing that it is a variation of the Pacific Needlefish. The differences between the two include: the keel under the tip of the chin (not present in the Pacific Needlefish), 24-26 dorsal fin rays (versus 21-23), 21-24 anal fin rays (versus 18-21), and 89-92 vertebrae (versus 74-80).
The Keeljaw Needlefish are viewed by locals as a pest with “too many bones” to be utilized for food. They are either a “catch and release” or retained for use as cut bait for bottom fishing. When hooked they like to make mad, short dashes. They are excellent bait stealers inflicting major damage to and weakening monofilament lines with their many teeth.