Hemiramphidae is a family of fishes that are commonly called halfbeaks, spipe fish or spipefish. They are a geographically widespread and numerically abundant family of epipelagic fish inhabiting warm waters around the world. The halfbeaks are named for their distinctive jaws, in which the lower jaws are significantly longer than the upper jaws. The similar viviparous halfbeaks (family Zenarchopteridae) have often been included in this family. Though not commercially important themselves, these forage fish support artisanal fisheries and local markets worldwide. They are also fed upon by other commercially important predatory fishes, such as billfishes, mackerels, and sharks.
Taxonomy
In 1758, Carl Linnaeus was the first to scientifically describe a halfbeak, Esox brasiliensis (now Hemiramphus brasiliensis). In 1775 Peter Forsskål described two more species as Esox, Esox far and Esox marginatus. In 1816, Georges Cuvier created the genus Hemiramphus; from then on, all three were classified as Hemiramphus. In 1859, Theodore Nicholas Gill erected the Hemiramphidae, deriving their name from Hemiramphus, the family's type genus. The name comes from the Greek hemi, meaning half, and rhamphos, meaning beak or bill. Currently, eight genera (including 60 species) are placed within the family Hemiramphidae:
Arrhamphus Günther, 1866 Chriodorus Goode & Bean, 1882 Euleptorhamphus Gill, 1859 Hemiramphus Cuvier, 1816 Hyporhamphus Gill, 1859 Melapedalion Fowler, 1934 Oxyporhamphus Gill, 1864 Rhynchorhamphus Fowler, 1928 This family is primarily marine and found in the Atlantic, Pacific, and Indian Oceans, though some inhabit estuaries and rivers.
Evolution The halfbeaks' fossil record extends into the Lower Tertiary. The earliest known halfbeak is "Hemiramphus" edwardsi from the Eocene at Monte Bolca, Italy, although its attribution to the extant Hemiramphus is doubtful. Apart from differences in the length of the upper and lower jaws, recent and fossil halfbeaks are distinguished by the fusion of the third pair of upper pharyngeal bones into a plate.
Phylogeny
The phylogeny of the halfbeaks is in a state of flux. On the one hand, there is little question that they are most closely related to three other families of streamlined, surface water fishes: the flyingfishes, needlefishes, and sauries. Traditionally, these four families have been taken to comprise the order Beloniformes. The halfbeaks and flyingfishes are considered to form one group, the superfamily Exocoetoidea, and the needlefishes and sauries another, the superfamily Scomberesocoidea. On the other hand, recent studies have demonstrated that rather than forming a single monophyletic group (a clade), the halfbeak family actually includes a number of lineages ancestral to the flyingfishes and the needlefishes. In other words, as traditionally defined, the halfbeak family is paraphyletic. Within the subfamily Hemiramphinae, the "flying halfbeak" genus Oxyporhamphus has proved to be particularly problematic; while morphologically closer to the flyingfishes, molecular evidence places it with Hemiramphus and Euleptorhamphus. Together, these three genera form the sister group to the flyingfish family. The other two hemiramphine genera Hyporhamphus and Arrhamphus form another clade of less clear placement. Rather than being closely related to the flyingfishes, the subfamily Zenarchopterinae appears to be the sister group of the needlefishes and sauries. This is based on the pharyngeal jaw apparatus, sperm ultrastructure, and molecular evidence. However, this hypothesis has awkward implications for how the morphological evolution of the group is understood, because the fused pharyngeal plate has been considered reliably diagnostic of the halfbeak family. Furthermore, the existing theory that because juvenile needlefish pass through a developmental stage where the lower jaw is longer than the upper jaw (the so-called "halfbeak stage") the theory that halfbeaks are paedomorphic needlefish is untenable. In fact the unequal lengths of the upper and lower jaws of halfbeaks appears to be the basal condition, with needlefish being relatively derived in comparison.
Morphology
The halfbeaks are elongated, streamlined fish adapted to living in open water. They can grow to over 40 cm (16 in) in standard length in the case of Euleptorhampus viridis. Their scales are relatively large, cycloid (smooth), and easily detached. No spines are in the fins. A distinguishing characteristic is that the third pair of upper pharyngeal bones is anklylosed (fused) into a plate. Halfbeaks are one of several fish families that lack a stomach, all of which possess a pharyngeal jaw apparatus (pharyngeal mill). Most species have an extended lower jaw, at least as juveniles, though this feature may be lost as the fish mature, as with Chriodorus, for example. As is typical for surface-dwelling, open-water fish, most species are silvery, darker above and lighter below, an example of countershading. The tip of the lower jaw is bright red or orange in most species. Halfbeaks carry several adaptations to feeding at the water surface. The eyes and nostrils are at the top of the head, and the upper jaw is mobile, but not the lower jaw. Combined with their streamlined shape and the concentration of fins towards the back (similar to that of a pike), these adaptations allow halfbeaks to locate, catch, and swallow food items very effectively.
Range and habitat
Halfbeaks inhabit warm seas, predominantly at the surface, in the Atlantic, Indian, and Pacific Oceans. A few are found in estuaries. Most species of marine halfbeaks are known from continental coastlines, but some extend into the western and central Pacific, and one species (Hyporhamphus ihi) is endemic to New Zealand. Hemiramphus is a worldwide marine genus.
Ecology and behavior
Feeding Marine halfbeaks are omnivores feeding on algae, marine plants such as seagrasses, plankton, invertebrates such as pteropods and crustaceans, and smaller fishes. For some subtropical species, at least, juveniles are more predatory than adults. Some tropical species feed on animals during the day and plants at night, while other species alternate between carnivory in the summer and herbivory in the winter. They are, in turn, eaten by many ecologically and commercially important fish, such as billfish, mackerel, and sharks, so are a key link between trophic levels.
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