Atlantic Needlefish, Strongylura marina
The Atlantic Needlefish, Strongylura marina, whose common Spanish name is agujón verde, is a member of the Needlefish or Belonidae Family, known collectively as agujones in Mexico. Globally, there are fourteen species in the genus Strongylura, four of which are found in Mexican waters, three in the Atlantic and one in the Pacific.
The Atlantic Needlefish have very elongated rounded bodies with extremely elongated jaws that form a long beak with numerous needle-like teeth. They are blue-green dorsally and transition to silvery ventrally. They have a black bar behind their eyes that only extends above the mid-line of the eyes. This countershading affords them camouflage to avoid predation. Their fins have no spines. They have no gill rakers. Their anal and dorsal fins have low lobes at the front. Their anal fin has 16 to 20 rays; their caudal fin is slightly concave; their dorsal fin has 14 to 17 rays; their pectoral fins are small; and their pelvic fins are rounded. Their body is covered with small scales.
The Atlantic Needlefish are found in the first 20 feet of the water column. They reach a maximum length of 1.11 meters (3 feet 8 inches) and 2.3 kg (5.1 pounds) in weight. They are found in areas with minimal current flow including reefs, mangrove-lined lagoons, and seagrass beds with a wide range of salinities including brackish estuaries and freshwater systems such as the rivers of Alabama, Maryland, Tennessee, and Texas. They are known to migrate from estuaries to oceanic waters during the winter and are prone to cold water kills. Adults are voracious predators feeding exclusively on fish; juveniles feed primarily on shrimp and small fish. They are preyed upon by the Atlantic Tarpon, Bottlenose Dolphin, Lemon Sharks, and various shore birds. Reproduction is oviparous with females laying large spherical eggs in shallow water habitats which attach themselves to floating vegetation such as Sargassum seaweed via long filamentous tendrils before being fertilized by males. The Atlantic Needlefish are of scientific interest for a variety of reasons. Their internal reproductive anatomy is unusual in that only the right gonad is developed in mature individuals. The evolution of the jaw structure is atypical with hatched larvae having short jaws of equal length, which then become halfbeaks as the lower jaw becomes elongated, and finally the larger juveniles become “needlenosed” with upper and lower jaws of equal length. In addition, they represent a species that has been able to transition from marine environments to freshwater environments.
In Mexican waters the Atlantic Needlefish are common being found in all waters of the Atlantic.
The Atlantic Needlefish can be confused with the Keeltail Needlefish, Platybelone argalus (very slender and elongated body), the Redfin Needlefish, Strongylura notata (reddish anal, caudal, and dorsal fins; 12 to 15 anal fin rays), and the Timucú, Strongylura timucu (overall darker in color; dark stripe mid-body).
From a conservation perspective, the Atlantic Needlefish are currently considered to be of Least Concern, with wide distribution, stable populations, and no fishing pressure. They are not commercially important and are caught by recreational anglers as a by-catch and only pursued if present in large size. They are used on a limited basis as live bait for marlin sportsfishing. They are considered a poor food fish due to their overabundant bones.
Atlantic Needlefish, Strongylura marina. Fish caught from coastal waters off Key Largo, Florida, December 2013. Length: 33 cm (13 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.
Atlantic Needlefish, Strongylura marina. Fish caught from coastal waters off Duck Key, Florida, January 2013. Length: 33 cm (13 inches). Catch, photo, and identification courtesy of Kenneth Tse, Toronto, Canada.