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Halfbeak

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

                        iHemiramphidae
   A marine halfbeak, the ballyhoo, Hemiramphus brasiliensis
   A marine halfbeak, the ballyhoo, Hemiramphus brasiliensis
                   Scientific classification

   Kingdom: Animalia
   Phylum:  Chordata
   Class:   Actinopterygii
   Order:   Beloniformes
   Family:  Hemiramphidae

                                   Genera

   Arrhamphus
   Chriodorus
   Dermogenys
   Euleptorhamphus
   Hemirhamphodon
   Hemiramphus
   Hyporhamphus
   Melapedalion
   Nomorhamphus
   Oxyporhamphus
   Rhynchorhamphus
   Reporhamphus
   Tondanichthys
   Zenarchopterus

   Halfbeaks (family Hemiramphidae) are an important family of epipelagic
   fish inhabiting warm waters around the world. The family is divided
   into two subfamilies, the Hemiramphinae and the Zenarchopterinae, each
   containing about half the known species. In a recent review of the
   family, two subfamilies, 14 genera, and 117 species and subspecies were
   recognised. Halfbeaks are named after their elongate jaws, the lower of
   which is usually significantly longer than the upper one, and it is
   this feature provides the family with its common name; the family name,
   Hemiramphidae, comes from the Greek hemi, meaning half, and rhamphos,
   meaning a beak or bill.

   The Hemiramphinae are primarily marine and found in the Atlantic,
   Pacific, and Indian Oceans, though some inhabit estuaries and rivers.
   The Zenarchopterinae are confined to the Indo-West Pacific
   zoogeographic region, an area running from East Africa to the Caroline
   Islands. The Zenarchopterinae are remarkable for exhibiting strong
   sexual dimorphism, practicing internal fertilisation, and in some cases
   being ovoviviparous or viviparous. Three genera in this subfamily are
   exclusively freshwater fish and several, such as the wrestling
   halfbeak, have become important aquarium fish.

   Marine halfbeaks are omnivores feeding on algae; marine plants such as
   seagrasses; plankton; invertebrates such as pteropods and crustaceans;
   and smaller fishes ; as such they form an important link between
   trophic levels and are eaten by many ecologically and commercially
   important predatory fish, such as billfish, mackerel, and sharks. They
   are not commonly fished for commercially, but many artisanal fisheries
   target halfbeaks, and their meat is considered to be of good quality.
   In some localities large bait fisheries exist to supply sport
   fishermen. Freshwater halfbeaks are believed to feed primarily on
   insects, particularly mosquitoes and spiders.

Phylogeny

   Halfbeaks are members of the Beloniformes and close relatives of the
   flyingfishes, needlefishes, and sauries. However, the precise
   relationships between these groups has been debated among systematists.
   Juvenile needlefish pass through a developmental stage where the lower
   jaw is longer than the upper jaw, sometimes known as the "halfbeak
   stage", so it has been hypothesised that halfbeaks are paedomorphic
   needlefish, that is, halfbeaks as adults retain characteristics of the
   juvenile stages of their ancestors, the needlefish. The alternate view
   is that the unequal lengths of the upper and lower jaws seen in
   halfbeaks is the basal condition, with needlefish being relatively
   derived in comparison.

Morphology

   The halfbeaks are long, streamlined fish adapted to living in open
   water. Halfbeaks range in size from 4 cm (e.g., Nomorhamphus brembachi)
   to over 40 cm (e.g., Hemiramphus saltator) and all have an elongate,
   highly streamlined shape. The scales are relatively large and cycloid,
   that is, smooth. A peculiarity shared by all halfbeaks that
   distinguishes them from the other fishes in the Beloniformes is that
   the third pair of upper pharyngeal bones are anklylosed (fused) into a
   plate. There are no spines in the fins. 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.

   Males of the livebearing species have anal fins modified into an
   andropodium that is used to direct sperm into the female.

   As is typical for surface dwelling, open water fish, most species are
   silvery, and darker above and lighter below, an example of
   countershading. Small patches of colour, particularly among males, are
   only found on the fins and the tip of the beak.

Distribution and ecology

   Halfbeaks are primarily found in warm seas, predominantly at the
   surface. A small number are found in estuaries and some species,
   including all the species in the genera Dermogenys, Hemirhamphodon, and
   Nomorhamphus, are confined to fresh water. Marine halfbeaks are known
   from the warm temperate and tropical parts of the Atlantic, Indian and
   Pacific Oceans, but most of the freshwater species come from Southeast
   Asia.

   The marine species feed on small fish, plankton, algae, and fragments
   of vegetation such as sea grasses. For some subtropical species at
   least, juveniles are more predatory than adults. Some tropical species
   have been observed to feed on animals during the day and plants at
   night, while other species alternate between carnivory in the summer
   and herbivory in the winter.

   The freshwater species are more exclusively predatory than the marine
   species, and typically orient themselves into the water current and
   take aquatic insect larvae, such as midge larvae, and small insects,
   such as flies that have fallen on the surface of the water.

Importance

   The larger species are widely used as food fish and the meat is
   excellent. Halfbeaks are an important link in the food chain between
   plankton and large, commercially important predatory fish, and are also
   important as baitfish for game species including dolphinfish and
   billfish. Some of the smaller freshwater species are also kept as
   aquarium fish.

Reproduction

   Halfbeaks exhibit a variety of reproductive strategies including
   egg-laying, ovoviparity, and viviparity. Marine halfbeaks 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 the seagrass meadows of Florida Bay. Juvenile marine halfbeaks are
   often very common in brackish water habitats such as mangroves and
   estuaries, only moving offshore once they reach a certain size.

   The freshwater halfbeaks of the general Dermogenys, Hemirhamphodon, and
   Nomorhamphus are all livebearers, that is, they do not lay eegs but
   instead produce well-developed free-swimming young. However, there is a
   great deal of variation in the details. Meisner and Burns identified no
   fewer than five distinct moders of viviparity in the freshwater
   halfbeaks:
     * Type 1: Fertilised eggs retained within the ovarian follicle.
       Superfetation, that is storage of sperm, does not occur. The eggs
       are provided with a large yolk sac and have little or no connection
       to the maternal blood supply. Example: Southeast Asian populations
       of Dermogenys pusilla.
     * Type 2: Fertilised eggs retained within the ovarian follicle.
       Superfetation does occur, with up to three broods resulting from a
       single mating. The eggs are provided with a small yolk sac but the
       embryos instead have a connection to the maternal supply through
       the coelomic cavity and pericardial sac. Examples: Dermogenys
       pusilla from Sabah and Dermogenys orientalis.
     * Type 3: Fertilised eggs retained within the ovarian follicle only
       for the early stages of development, with the embryos later
       developing along the full length of the ovary. Superfetation does
       occur, and up to two broods can develop simultaneously in the
       ovary. The eggs are provided with a small yolk sac but the embryos
       have a connection to the maternal supply through an expanded belly
       sac. Example: Dermogenys viviparus.
     * Type 4: Fertilised eggs retained within the ovarian follicle only
       for the early stages of development, with the embryos later
       developing along the full length of the ovary. Superfetation does
       not occur. The eggs are provided with a large yolk sac and the
       embryos have no connection to the maternal blood supply. Examples:
       Nomorhamphus megarrhamphus, Nomorhamphus weberi, and Nomorhamphus
       towoetii.
     * Type 5: Fertilised eggs retained within the ovarian follicle only
       for the early stages of development, with the embryos later
       developing along the full length of the ovary. Superfetation does
       occur, and embryos of different ages can be found in the ovaries.
       The eggs are provided with a small yolk sac and the embryos only
       have a connection to the maternal blood supply for only part of
       their development. Late-stage embryos apparently eat eggs and small
       embryos in ovary. Note that embryos eating eggs and other embryos
       has been observed in a few other fishes, most notably sharks (see
       article on oophagy). Example: Nomorhamphus ebrardtii.

   Young freshwater halfbeak, Nomorhamphus sp., aged 7 days, approximately
   18 mm in length. Captive bred specimen.
   Enlarge
   Young freshwater halfbeak, Nomorhamphus sp., aged 7 days, approximately
   18 mm in length. Captive bred specimen.

   As with other livebearing fish, freshwater halfbeaks produce small
   broods of large offspring compared with egg-laying species of similar
   size, with broods of around ten to twenty, 10-15 mm long offspring
   being typical. Males of the ovovivaparous and vivaparous species all
   have a modified anal fin, the andropodium, similar to the gonopodium of
   poecilid livebearers, used to deliver sperm to the females. Although
   most of the egg laying species mate by shedding the milt externally, as
   is typical for bony fish, at least some egg-laying species practise
   internal fertilisation: male Zenarchopterus use a modified anal fin to
   direct sperm into the genital opening of the female prior to spawning .
   Halfbeaks therefore show the full range of reproductive methods know to
   occur in fishes: external fertilisation with egg laying; internal
   fertilisation with egg laying; internal fertilisation with
   ovoviviparity; and internal fertilisation with viviparity.

   Besides modifications to the anal fin, sexual dimorphism is quite
   strong in some species, especially among the livebearing freshwater
   halfbeaks. Female Normorhamphus are much larger than males but aren't
   as brightly coloured and have shorter beaks. By contrast, male
   Hemirhamphodon are larger than the females, and some species, such as
   Hemirhamphodon pogonognathus, also have a long beard-like tassle on the
   end of the beak.

Halfbeaks in aquaria

   Species of the genera Dermogenys and Nomorhamphus are quite commonly
   kept as aquarium fish; species of Hemirhamphodon and Zenarchopterus are
   rather less commonly seen. They are small and generally peaceful
   towards other species, although males can be aggressive to one another.
   Male Dermogenys pusillius in particular fight vigorously and sometimes
   these battles end in injuries; this fish has therefore become known as
   the wrestling halfbeak and in some Asian countries fights between males
   are used for betting purposes in much the same way as the Siamese
   fighting fish.

   To be kept successfully, halfbeaks require an aquarium with plenty of
   space at the surface. Depth is not critical, so a tank that is wide is
   better than one that is deep. They are sensitive to low oxygen levels
   but are otherwise relatively hardy, with one important exception: they
   do not tolerate sudden changes in salinity, pH, hardness, or
   temperature well. They must be introduced to a new aquarium gently, and
   subsequent water changes are best small but frequent so that the water
   chemistry does not suddenly change. Some species, most notably
   Dermogenys pusillius, are said to do best in slightly brackish water,
   but most species need moderately hard to soft, neutral to slightly
   acidic, water.

   Halfbeaks are nervous fish and things like switching on lights can
   cause them to swim around the tank frantically. They may hit themselves
   on the glass, injuring their beaks, or jump out of the tank completely.
   Injuries to the beak usually heal within a few weeks. They will eat
   insect larvae such as bloodworms readily, as well as crustacean eggs,
   shrimps, fruit flies, and even small pieces of chopped white fish.
   Halfbeaks sometimes eat flake foods as well. Some aquarists also offer
   them tiny pieces of algae wafer on the basis that most species are
   omnivorous in the wild, and so a certain amount of green food probably
   does them good.

   Halfbeaks will breed in captivity, but despite being livebearers they
   are not particularly easy to breed. Miscarriages are common,
   particularly if the females are stressed or shocked (for example, by
   being moved to another aquarium). Once the fry have been born, things
   get much simpler, as the baby halfbeaks are quite big and will eat
   newly hatched brine shrimps, small live foods such as daphnia, and
   powdered flake.

Images of halfbeaks

   Female Dermogenys sumatrana
   Enlarge
   Female Dermogenys sumatrana
   Female Dermogenys sumatrana a day or so before giving birth
   Enlarge
   Female Dermogenys sumatrana a day or so before giving birth
   A school of marine halfbeaks, Hemirhamphus sp.
   Enlarge
   A school of marine halfbeaks, Hemirhamphus sp.

   Hemirhamphus pacificus in an exhibit at the Walter Rothschild
   Zoological Museum
   Enlarge
   Hemirhamphus pacificus in an exhibit at the Walter Rothschild
   Zoological Museum
   Female Hemirhamphodon pogonognathus
   Enlarge
   Female Hemirhamphodon pogonognathus
   Subadult female Hemirhamphodon pogonognathus at rear with a juvenile
   male Dermogenys in front. The difference in beak length between these
   two genera is obvious
   Enlarge
   Subadult female Hemirhamphodon pogonognathus at rear with a juvenile
   male Dermogenys in front. The difference in beak length between these
   two genera is obvious

   Hemirhamphodon (left) and Dermogenys (right) compared
   Enlarge
   Hemirhamphodon (left) and Dermogenys (right) compared
   Male Nomorhamphus spp. fighting
   Enlarge
   Male Nomorhamphus spp. fighting
   Nomorhamphus liemi liemi halfbeaks ready for introduction to a new
   aquarium
   Enlarge
   Nomorhamphus liemi liemi halfbeaks ready for introduction to a new
   aquarium

   Retrieved from " http://en.wikipedia.org/wiki/Halfbeak"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
