Astyanax abramis
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| Astyanax abramis | |
|---|---|
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Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Acestrorhamphidae |
| Genus: | Astyanax |
| Species: | A. abramis |
| Binomial name | |
| Astyanax abramis | |
| Synonyms[2] | |
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Astyanax abramis is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins. This fish is found in the inland rivers of South America. It is plentiful in almost the entire continent, with a habitat including the La Plata, upper Amazon, and Meta River basins. The body shape is subrhomboidal (somewhat rhomboidal) and laterally compressed, and the scales are largely silver, with a blue or green tint on the dorsal side.
As a cryptic species, A. abramis could possibly constitute multiple species that are currently undescribed. A. abramis is also a part of a species complex that includes itself and various congeners, including Astyanax bimaculatus, the namesake of the complex, and Astyanax lacustris, which is very closely related to A. abramis and looks very similar. Astyanax is a particularly speciose genus wherein cryptics and complexes are not uncommon.
Sexual dimorphism
Abramis astyanax is a small fish that has a maximum recorded length of 14 cm (5.5 in) in standard length (SL) and a maximum recorded weight of 29.7 g (1.05 oz).[3] The body is compressed laterally and is subrhomboidal. It is a silvery fish with a green or blue tint on the back, and there is a dark spot, starting on the caudal peduncle, that reaches the posterior margin of the caudal fin.[4] Its fins, while largely transparent, can also have a slight red, orange, or yellow tint.[5]
There is a dark humeral spot on each side behind the top of the head ("humeral" means "around or related to the shoulder", as in "humerus"). This spot manifests as a horizontal oval, and the humeral region also sports two vertical brown bars. There is a black lateral stripe, just above the lateral line, that starts at the humeral spot or just behind it.[6]
Morphometric characteristics include 1 dorsal-fin spine, 10 dorsal-fin rays, and 30 to 34 anal-fin rays. A. abramis also has 42 to 48 lateral-line scales; this can be used to differentiate it from closely related congener A. lacustris, which has 36 to 39.[4] The scales are generally small, with concentric grooves near the posterior margin.[5] A. abramis lacks maxillary teeth, which can be used to tell it apart from various other similar congeners;[7] however, the premaxilla still sports teeth, and A. abramis is believed to demonstrate unilateral replacement of missing teeth.[8]
While there are few morphometric differences between the sexes, male A. abramis can be distinguished from female by the presence of small hooks or barbs on the anal-fin rays of male specimens.[5] Females also tend to be more common than males.[9]
Taxonomy
When first described, A. abramis was given the basionym Tetragonopterus abramis.[10] English naturalist Leonard Jenyns prescribed this name in 1842, building from the work of well-known English natural historian Charles Darwin, who collected the type specimens in the 19th century.[5][11] At one point, it was described as a separate species under the name Bertoniolus paraguayensis, but this name has been synonymized with A. abramis.[12] In 2016, its classification as a species was confirmed as valid, and it received a redescription.[13]
Within Astyanax, there are three subgenera - Astyanax stricto sensu, Poecilurichthys, and Zygogaster.[14] A. abramis belongs to Poecilurichthys.[citation needed]
Multiple species in the genus Astyanax are considered cryptic - that is, two or more possible species that are currently considered synonymous because of remarkable similarity, but that cannot reproduce with each other. A. abramis is no exception to this and is considered a cryptic species.[4] It is also a part of the Astyanax bimaculatus species complex, alongside Astyanax lacustris.[15]
At the time of description, Jupiaba species J. abramoides was believed to be closely related to A. abramis. This is the origin of its specific epithet - "oides" means "having the shape of".[16] The basionym of J. abramoides is, in fact, Astyanax abramoides.[17]
Etymology and nomenclature
The specific name "abramis" is an allusion to European species Abramis brama, a leuciscid that has a similar body shape (described as "subrhomboidal"). The genus name "Astyanax" comes from a figure in Homer's Iliad, Astyanax, who was the son of Hector, a famed Trojan warrior. Why the genus has this name was not made clear in the original text, but could possibly refer to the large, armor-like scales of species A. argentatus.[18]
In terms of a common name, A. abramis is one of various species of Astyanax referred to as "lambari".[4]
Distribution and habitat
Astyanax abramis can be found in the La Plata basin, as well as the upper Amazon and Meta River basins. It is most often found in lentic (still water) environments.[3] Lentic environments, without the oxygenation provided by flowing water, are generally lower in dissolved oxygen, which has resulted in A. abramis developing adaptations to such conditions, including morphological plasticity (albeit limited).[19]
The relevant habitat stretches through multiple countries, including Brazil, Argentina, Bolivia, Uruguay, and Paraguay.[5] Specific rivers, regions, and tributaries include the Juramento,[20] Yabotí,[21] and Parana.[6]