| Halfbeak | |
|---|---|
 | |
| Ballyhoo (Hemiramphus brasiliensis), a marine halfbeak | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Beloniformes |
| Superfamily: | Exocoetoidea |
| Family: | Hemiramphidae T. N. Gill, 1859 |
| Genera | |
see text | |
Hemiramphidae is afamily offishes that are commonly calledhalfbeaks,spipe fish orspipefish. They are a geographically widespread and numerically abundant family ofepipelagic 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 similarviviparous halfbeaks (family Zenarchopteridae) have often been included in this family.
Though notcommercially important themselves, theseforage fish supportartisanal fisheries and local markets worldwide. They are also fed upon by other commercially importantpredatory fishes, such asbillfishes,mackerels, andsharks.
In 1758,Carl Linnaeus was the first toscientifically describe a halfbeak,Esox brasiliensis (nowHemiramphus brasiliensis). In 1775Peter Forsskål described two morespecies asEsox,Esox far andEsox marginatus. It was not until 1816 thatGeorges Cuvier created thegenusHemiramphus; from then on, all three were classified asHemiramphus. In 1859,Gill erected Hemiramphidae, deriving its name fromHemiramphus, the family'stype genus.[1] The name comes from theGreekhemi, meaning half, andrhamphos, meaning beak or bill.[2]
There are currently eight genera (including 60 species) within the family Hemirampphidae:[3]
This family is primarilymarine and found in theAtlantic,Pacific, andIndian Oceans, though some inhabitestuaries andrivers.
The halfbeaks'fossil record extends into theLower Tertiary.[2] The earliest known halfbeak is"Hemiramphus"edwardsi from theEocene atMonte Bolca,Italy, although its attribution to the extantHemiramphus is doubtful.[4] 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 upperpharyngeal bones into a plate.[5]
| Phylogeny of the halfbeaks. |
Thephylogeny 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: theflyingfishes,needlefishes, andsauries.[6] Traditionally, these four families have been taken to together comprise the orderBeloniformes.[6] The halfbeaks and flyingfishes are considered to form one group, the superfamilyExocoetoidea, and the needlefishes and sauries another, the superfamilyScomberesocoidea.[7]
On the other hand, recent studies have demonstrated that rather than forming a singlemonophyletic group (aclade), 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 isparaphyletic.[5]
Within the subfamily Hemiramphinae, the "flying halfbeak" genusOxyporhamphus has proved to be particularly problematic; whilemorphologically closer to the flyingfishes, molecular evidence places it withHemiramphus andEuleptorhamphus. Together, these three genera form thesister group to the flyingfish family.[5] The other two hemiramphine generaHyporhamphus andArrhamphus form another clade of less clear placement.[5]
Rather than being closely related to the flyingfishes, the subfamily Zenarchopterinae appears to be the sister group of theneedlefishes andsauries. 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.[5] Furthermore, the existing theory that because juvenile needlefish pass through adevelopmental stage where the lower jaw is longer than the upper jaw (the so-called "halfbeak stage") the theory that halfbeaks arepaedomorphic needlefish is untenable.[5] In fact the unequal lengths of the upper and lower jaws of halfbeaks appears to be thebasal condition, with needlefish being relativelyderived in comparison.[5][8]
The halfbeaks are elongate, streamlined fish adapted to living in open water. Halfbeaks can grow to over 40 centimeters (16 in) SL in the case ofEuleptorhampus viridis. Thescales are relatively large,cycloid (smooth), and easily detached. There are no spines in the fins.[1] A distinguishing characteristic is that the third pair of upper pharyngeal bones are anklylosed (fused) into a plate. Halfbeaks are one of several fish families that lack astomach, all of which possess a pharyngeal jaw apparatus (pharyngeal mill).[7] Most species have an extended lower jaw, at least as juveniles, though this feature may be lost as the fish mature, as withChriodorus, for example.[5]
As is typical for surface dwelling, open water fish, most species are silvery, darker above and lighter below, an example ofcountershading. The tip of the lower jaw is bright red or orange in most species.[1]
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 apike), these adaptations allow halfbeaks to locate, catch, and swallow food items very effectively.[9]
Halfbeaks inhabit warm seas, predominantly at the surface, in theAtlantic,Indian, andPacific oceans.[7] A small number are found inestuaries. Most species of marine halfbeaks are known from continental coastlines, but some extend into the western and centralPacific, and one species (Hyporhamphus ihi) isendemic toNew Zealand.[7]Hemiramphus is a worldwide marine genus.[2]
Marine halfbeaks areomnivores feeding onalgae; marine plants such asseagrasses;plankton; invertebrates such aspteropods andcrustaceans; and smaller fishes.[10] 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.[11] They are in turn eaten by many ecologically andcommercially important fish, such asbillfish,mackerel, andsharks, and so are a key link betweentrophic levels.[12]
Marine halfbeaks are typicallypelagicschoolingforage fish.[13][14] The southern sea garfishHyporhamphus melanochir for example is found in sheltered bays, coastal seas, estuaries around southern Australia in waters down to a depth of 20 meters (66 ft). These fish school near the surface at night but swim closer to the sea floor during the day, particularly among beds ofseagrasses.[15] Genetic analysis of the differentsub-populations of the eastern sea garfishHyporhamphus melanochir inSouth Australian coastal waters reveals that there is a small but consistent migration of individuals among theme, sufficient to keep them genetically homogeneous.[13]
Some marine halfbeaks, includingEuleptorhamphus velox andEuleptorhamphus viridis, are known for their ability to jump out of the water and glide over the surface for considerable distances, and have consequently sometimes been calledflying halfbeaks.[2][16][17]
Hemiramphidae species are allexternal fertilizers.[7] They are usually egg-layers and often produce relatively small numbers of fairly large eggs for fish of their size, typically in shallow coastal waters, such as theseagrass meadows ofFlorida Bay.[18] The eggs ofHemiramphus brasiliensis andH. balao are typically 1.5–2.5 mm (0.059–0.098 in) in diameter and have attaching filaments. They hatch when they grow to about 4.8–11 mm (0.19–0.43 in) in diameter.[1]Hyporhamphus melanochir eggs are slightly larger, around 2.9 mm (0.11 in) in diameter, and are unusually large when they hatch, being up to 8.5 mm (0.33 in) in size.[15]
Relatively little is known about the ecology of juvenile marine halfbeaks, though estuarine habitats seem to be favored by at least some species.[15][18] The southern sea garfishHyporhamphus melanochir grows rapidly at first, attaining a length of up to 30 cm (12 in) in the first three years, after which point growth slows.[15] This species lives for a maximum age of about 9 years, at which point the fish reach up to 40 cm (16 in) and weigh about 0.35 kg (0.77 lb).[15]
Halfbeaks are not a major target forcommercial fisheries, though small fisheries for them exist in some places, for example inSouth Australia where fisheries target the southern sea garfish (Hyporhamphus melanochir).[13] and the eastern sea garfish (Hyporhamphus australis).[14] Halfbeaks are caught by a variety of methods includingseines and pelagictrawls, dip-netting under lights at night, and with haul nets.[1] They are utilized fresh, dried, smoked, or salted,[1][13][14] and they are considered good eating. However, even where halfbeaks are targeted by fisheries, they tend to be of secondary importance compared with other edible fish species.[15]
In some localities significantbait fisheries exist to supplysport fishermen.[1][11][12] One study of a bait fishery in Florida that targetsHemiramphus brasiliensis andHemiramphus balao suggests that despite increases in the size of the fishery the population is stable and the annual catch is valued at around $500,000.[12][19]
