''Danionella'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of danionin fish found in freshwater habitats in

Myanmar Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...

and

West Bengal West Bengal (; Bengali language, Bengali: , , abbr. WB) is a States and union territories of India, state in the East India, eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabi ...

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 ...

. It includes some of the smallest fishes.

Distribution

Four out of five described species of ''Danionella'' are found in Myanmar. ''D. translucida'' is described from the

Ayeyarwady River The Irrawaddy River (, , Ayeyarwady) is the principal river of Myanmar, running through the centre of the country. Myanmar’s most important commercial waterway, it is about 1,350 miles (2,170 km) long. Originating from the confluence of the ...

basin, and ''D. mirifica'' was described from the Kamaing area in

upper Myanmar Upper Myanmar ( or , also called Upper Burma) is one of two geographic regions in Myanmar, the other being Lower Myanmar. Located in the country's centre and north stretches, Upper Myanmar encompasses six inland states and regions, including M ...

. '' Danionella priapus'' 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 India.

Description

When first described, ''Danionella translucida'' was the smallest ostariophysan and the smallest adult

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

to inhabit

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...

. Its adult size ranges from 10–12 millimetres (.43–.47 in) SL. ''D. mirifica'' gets slightly larger, at about 14 mm (.55 in) SL, but is still one of the smallest freshwater fishes. ''Danionella'' species lack

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...

and barbels, but possess a

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...

. ''D. mirifica'' has a single row of melanophores between the pelvic fins and the tips of the cleithra, and there is a lack of melanophores on the underside of the abdomen. ''D. dracula'' reaches 17 mm in length. It is neotonous, lacking 44 bones that develop late in the related zebrafish ''

Danio rerio The zebrafish (''Danio rerio'') is a species of freshwater ray-finned fish belonging to the family Danionidae of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio (a ...

.'' They have teeth made of bone, rather than the true teeth of other fishes, and the males have a pair of boney fangs which may be used during male-male competitions over nesting sites. Britz ''et al.'' believe the lineage lost true teeth about 50 Ma.

As a model organism

Danionella is used in scientific experiments as it is small, optically transparent throughout its lifespan, genetically amenable and has a short generation time.

Species

* *

References

* {{Taxonbar, from=Q138091 Danioninae Taxa named by Tyson R. Roberts