''Garra ceylonensis'' (the stone sucker or Ceylon logsucker) is a species of

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

in the

cyprinid Cyprinidae is a Family (biology), family of freshwater fish commonly called the carp or minnow family, including the carps, the true minnows, and their relatives the barb (fish), barbs and barbel (fish), barbels, among others. Cyprinidae is the ...

family. It is

endemic Endemism is the state of a species being found only 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 foun ...

to rivers and streams in

Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...

(formerly known as "Ceylon") - and is considered as a schooling fish. It is a

rheophilic A rheophile is an animal that prefers to live in fast-moving water. Examples of rheophilic animals Insects *Many aquatic insects living in riffles require current to survive. *'' Epeorus sylvicola'', a rheophilic mayfly species ( Ephemeroptera ...

species and occurs in slow to moderately flowing rivers and streams, and ascends small, rocky streams in order to breed. It primarily feeds on aufwuchs - algae and

diatoms A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

Taxonomy

A 2021 study found ''G. ceylonensis'' to be a

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to the mullya garra (''Garra mullya'') from mainland

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

, which itself may comprise two species. ''G. ceylonensis'' comprises primarily six genetically distinct

subclades In genetics, a subclade is a subgroup of a haplogroup. Naming convention Although human mitochondrial DNA (mtDNA) and Y chromosome DNA (Y-DNA) haplogroups and subclades are named in a similar manner, their names belong to completely separate syste ...

that are each tied to a single river basin, albeit with two exceptions.

Evolution

The ancestor of ''G. ceylonensis'' colonized Sri Lanka from India once during the

late Pliocene Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...

, via a former

isthmus An isthmus (; : isthmuses or isthmi) is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated. A tombolo is an isthmus that consists of a spit or bar, and a strait is the sea count ...

that existed in the

Palk Strait Palk Strait is a strait between the Indian state of Tamil Nadu and Northern Province of Sri Lanka. It connects the Palk Bay in the Bay of Bengal in the north with the Gulf of Mannar in the Laccadive sea in the south. It stretches for about ...

, and from the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

until its submergence, the still-exposed isthmus may have had a hydroclimate unsuitable to further dispersal of freshwater fish. During the Pleistocene, a major

aridification Aridification is the process of a region becoming increasingly arid, or dry. It refers to long term change, rather than seasonal variation. It is often measured as the reduction of average soil moisture content. It can be caused by reduced preci ...

event led to the

extirpation Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with extinction, global extinctions. Local extinctions ...

of many ancestral ''G. ceylonensis'' populations, leading it to be restricted to several

relict A relict is a surviving remnant of a natural phenomenon. Biology A relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas. Geology and geomorphology In geology, a r ...

populations. When the climate became more suitable, the species recolonized most of the island, which may have been facilitated by

stream capture Stream capture, river capture, river piracy or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows down to the bed of a neighbouring stream. This ...

and the species' free-swimming larvae.

Status

''G. ceylonensis'' is considered

near threatened A near-threatened species is a species which has been Conservation status, categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature (IUCN) as that may be vulnerable to Endangered species, endangerment in the ne ...

on the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

. The species is frequently exploited for the

aquarium trade Fishkeeping is a popular hobby, practiced by aquarists, concerned with keeping fish in a home aquarium or garden pond. It is a practice that encompasses the art of maintaining one's own aquatic ecosystem, featuring a lot of variety with various ...

, and there have been major changes to its habitat from

deforestation Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...

and

hydropower Hydropower (from Ancient Greek -, "water"), also known as water power or water energy, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, ...

projects that block its migration routes.

References

{{Taxonbar, from=Q3758528 Garra Freshwater fish of Sri Lanka Taxa named by Pieter Bleeker Fish described in 1863