| Handfish | |
|---|---|
 | |
| Brachionichthys hirsutus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Lophiiformes |
| Suborder: | Antennarioidei |
| Family: | Brachionichthyidae T. N. Gill, 1878 |
| Genera | |
see text | |
Handfish are marineray-finned fishes belonging to thefamilyBrachionichthyidae, a group which comprises fivegenera and 14 extant species and which is classified within the suborder Antennarioidei in the orderLophiiformes, the anglerfishes.[2] Thesebenthic marine fish are unusual in the way they propel themselves by walking on the sea floor rather than swimming.
The handfish were first proposed as a family, Brachionichthyidae, in 1878 by the AmericanichthyologistTheodore Gill.[3] The Brachionichthyidae is classified within thesuborderAntennarioidei within theorderLophiiformes, the anglerfishes.[4] The Brachionichthyidae is regarded as the mostbasal family within the suborder Antennarioidei.[5]
The handfish family, Brachionichthyidae, contains the following genera:[4][6]
Handfish are found today in the coastal waters of southern and easternAustralia and around the island state ofTasmania. This is the most species-rich of the few marine fish familiesendemic to the Australian region, with all but three species found there.[8] There are 14 species of handfish around Tasmania.[9]
The biology of handfishes is poorly known and their typically small population sizes and restricted distributions make them highly vulnerable to disturbance. Some species are considered to be critically endangered.[10]
Handfish grow up to 15 cm (5.9 in) long, and have skin covered withdenticles (tooth-likescales), giving them the alternative namewarty anglers. They are slow-moving fish that prefer to 'walk' rather than swim, using their modifiedpectoral fins to move about on the sea floor. These highly modified fins have the appearance of hands, hence their scientific name, fromLatinbracchium meaning "arm" andGreekichthys meaning "fish".[citation needed]
Like other anglerfish, they possess anillicium, a modifieddorsal fin ray above the mouth, but it is short and does not appear to be used as afishing lure.[dubious –discuss][1] The second dorsal spine is joined to the third by a flap of skin, making a crest.[11]
The prehistoric species,Histionotophorus bassani, from theLutetian ofMonte Bolca, is now considered to be a handfish, sometimes even being included in the genusBrachionichthys. Considering the low extant diversity, restricted geographical distribution, and very meagre fossil record of antennarioids in general, the existence of fossil representatives of the family Brachionichthyidae is unusual.[10]
In 1996, thespotted handfish (Brachionichthys hirsutus) was the first marine fish to be listed as critically endangered in the IUCN Red List.[12][13] With its only habitat in theDerwent River estuary and surrounds, it is threatened by theNorthern Pacific seastar's invasion into southern Australian waters. TheNorthern Pacific seastar (Asterias amurensis), preys on not only the fish eggs,[14] but also on the sea squirts (ascidians)[15] that help to form thesubstrate that the fish spawn on.[16]
The cause of the decline in spotted handfish is unclear. Suggested causes may include disturbance of benthic communities and predation on egg masses by the introducednorthern Pacific seastar, habitat modification through increasedsiltation,heavy metal contamination or urbaneffluent. The lack of a pelagic larval stage and low rates of dispersal may be responsible for their restricted distributions and may also have an impact on handfishes ability to recolonise areas where they once occurred.[8]
In March 2020, thesmooth handfish (Sympterichthys unipennis) was declared extinct in theIUCN Red List.[17][12] Once common enough to be one of the first fish to be described by European explorers of Australia, but not seen for well over a century, this is the first modern-day marine fish to be officially declared extinct.[12] However, this was reversed in September 2021, as there is not sufficient data to confirm this status.[18][19]
In October 2021, the endangered and very rarepink handfish (Brachiopsilus dianthus[20]) was seen for the first time since 1999, in footage from a camera placed on the sea bed off Tasmania at a depth of 150 m (490 ft). Prior to this sighting, it had been assumed that this species was confined to shallow waters. The discovery that it has a greater range than previously thought may give cause for optimism regarding its survival.[9]
As of December 2021[update] three species of handfish are listed asthreatened under theEnvironment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and the IUCN:[8]
All three of the above are listed as Endangered under the TasmanianThreatened Species Protection Act 1995,[21][22][23] and all handfish species are protected under the TasmanianLiving Marine Resources Management Act 1995, which prohibits their collection in State waters without a permit.[8]
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