Keeltail Needlefish, Platybelone argalus
The Keeltail Needlefish, Platybelone argalus, whose common Spanish name is agujón de quilla, is a species in the Needlefish or Belonidae Family, known collectively as agujónes in Mexico. Globally, there are only seven species in the genus Platybelone, one of which is found in Mexican waters, this species in both the Atlantic and the Pacific.
The Keeltail Needlefish are one of the more exotic and unique fish in Mexico. They have an extremely elongated cylindrical body that is greenish blue on the upper back and abruptly transitions to silvery well above the mid-body. They have very long beaks (25-27% of standard length) and their lower jaw is significantly longer than their upper jaw. They have small teeth. Their tail base is flattened with a large lateral keel, after which they are named, that is at least three times wider than it is deep. Their caudal fin is slightly forked with the lower lobe being slightly larger than the upper lobe. Their pectoral and pelvic fins are short.
The Keeltail Needlefish are an oceanic pelagic fish found in the first 15 feet of the water column. They reach a maximum length of 50 cm (20 inches). They are a very rare species and very little is known about their behavior.
In Mexican waters the Keeltail Needlefish are found from San Quintin southward along the northwest, central and southwest coasts of Baja, in the southern half of the Sea of Cortez, and along the coast of the mainland from Acapulco south to Guatemala.
Due to the unique shape of their tail base and to their elongated slender body, the Keeltail Needlefish cannot be confused with any other Needlefish.
The Keeltail Needlefish is too rare and too small to be of interest to most.