''Kuhlia xenura'', the strange-tailed flagtail or Hawaii flagtail, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

, a

flagtail The flagtails (' or ' in the Hawaiian language) are a family (Kuhliidae) of perciform fish of the Indo-Pacific area. The family consists of several species in one genus, ''Kuhlia''. Most are euryhaline and often found in brackish water, but th ...

from the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Kuhliidae The flagtails (' or ' in the Hawaiian language) are a family (Kuhliidae) of perciform fish of the Indo-Pacific area. The family consists of several species in one genus, ''Kuhlia''. Most are euryhaline and often found in brackish water, but th ...

which is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

, where it occurs in fresh,

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

, and

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

waters. It can be found in

tide pools A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. Many of these pools exist as separate bodies of water only at low tide. Many tide pool habitats are home to especially adaptable animals that ...

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

, and on

reefs A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock out ...

occurring over sand or rock.

Description

''Kuhlia xenura'' has a slightly concave dorsal profile of the head in adults, with a large eye. The second spine in the

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

is around 90% of the length of the third. The

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

is deeply forked. This species is silver in colour with a dark grey or dusky caudal fin which has a thin black rear margin and frequently shows a pale submarginal band. The

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

has 10 spines and 10 soft rays while the anal fin has three spines and 10-11 soft rays. This species grows to a

standard length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish m ...

of .

Distribution

''Kuhlia xenura'' is endemic to Hawaii.

Habitat and biology

''Kuhlia xenura'' is frequently observed in schools and can be found in fresh water, brackish habitats, and shallow water along the seashore. While in fresh water they feed mainly on algae, insects, planktonic crustaceans, and foraminiferans, while fish in brackish or salt water eat

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...

, insects,

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

larvae, algae,

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

s, and

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...

s. Medium sized fish, with a

total length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish ...

of , occur in deeper water at the foot of exposed cliffs, in larger tidal pools, or in rivers or ponds. These fish have a diet dominated by crustacean larvae, especially the later stages of crabs and

stomatopod Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in leng ...

s. They also eat small amounts of insects and algae. Fish larger than a total length of are found in surf exposed cliffs, in caves in outer reefs, and other exposed localities, where they feed largely on crustaceans and

polychaete Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...

worms. This species is mainly nocturnal. Spawning occurs all year, but peaks between December and June and it appears to occur at sea.

Taxonomy

The strange-tailed flagtail was previously confused with the

Hawaiian flagtail The Hawaiian flagtails are species of the genus of flagtail fishes found in the Hawaiian Islands. Two species are ''Kuhlia sandvicensis'' and '' K. xenura''. ''K. xenura'' is endemic to the islands. In the Hawaiian language, ''āholehole'' refe ...

until 2001. It was first described as ''Xenichthys xenurus'' on the basis of a specimen mistakenly thought to have come from

San Salvador San Salvador (; ) is the capital and the largest city of El Salvador and its eponymous department. It is the country's political, cultural, educational and financial center. The Metropolitan Area of San Salvador, which comprises the capital i ...

El Salvador El Salvador (; , meaning " The Saviour"), officially the Republic of El Salvador ( es, República de El Salvador), is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south b ...

. For over a century, the name ''Xenichthys xenurus'' was overlooked in the literature, and ''K. xenura'' was confused with ''K. sandvicensis'' by many authors.Randall, J.E., 1996. Shore fishes of Hawai'i. Natural World Press, Vida, Oregon. 216 p. In 2001, the ichthyologist

John Ernest Randall John Ernest "Jack" Randall (May 22, 1924 – April 26, 2020) was an American ichthyologist and a leading authority on coral reef fishes. Randall described over 800 species and authored 11 books and over 900 scientific papers and popular articles. ...

and his wife Helen Randall reviewed all nominal flagtail species from the Pacific Ocean. They found that two species had been lumped together under ''Kuhlia sandvicensis'', one of which had been misidentified as the freshwater ''K. marginata'' by some authors (the true ''K. sandvicensis''). They found that specimens of the common flagtail species from the Hawaiian Islands misidentified as ''K. sandvicensis'' matched the description of ''Xenichthys xenurus'', and thus ''Kuhlia xenura'' became the correct name for one of the two flagtail species from Hawaii.>

References

{{Taxonbar, from=Q1973502 Kuhliidae Taxa named by David Starr Jordan Taxa named by Charles Henry Gilbert Fish described in 1882