Astyanax caucanus
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| Astyanax caucanus | |
|---|---|
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Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Acestrorhamphidae |
| Genus: | Astyanax |
| Species: | A. caucanus |
| Binomial name | |
| Astyanax caucanus (Steindachner, 1879) | |
| Synonyms[2] | |
| |
Astyanax caucanus is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins. This fish is endemic to Colombia. While little research exists regarding its ecological habits, such as diet and mating practices, its environment preferences are known to include marshy lowlands, and it easily lives in sympatry with various other fish species in the Cauca and Magdalena river basins. It is not known to share a habitat with any other species of Astyanax, but has a noted phyletic relationship to a group of congeners including Astyanax filiferus, Astyanax stilbe, and Astyanax magdalenae.
Congener Astyanax atratoensis has been noted to bear a strong visual resemblance to A. caucanus, and researchers as early as 1908 were commenting on a possible relationship. It is unknown if this remains the case, as A. atratoensis and A. caucanus no longer share a subgenus; A. caucanus has been considered a member of subgenus Zygogaster since its description, and A. atratoensis has been moved from Zygogaster to Poecilurichthys by recent research.
Etymology
When originally described by Austrian ichthyologist Franz Steindachner in 1879, A. caucanus was assigned the name Tetragonopterus caucanus.[3] Otherwise, it lacks any synonyms.[4]
There are three subgenera in Astyanax - Astyanax, Poecilurichthys, and Zygogaster[5] - and A. caucanus has been placed in Zygogaster, making its full name Astyanax (Zygogaster) caucanus. Four other species originally shared this subgenus: Astyanax stilbe, Astyanax atratoensis, Astyanax magdalenae, and Astyanax filiferus.[6] In 1908, German-American ichthyologist Carl H. Eigenmann remarked that A. atratoensis may be one of the more closely related species to A. caucanus.[7] Based on modern understandings, this may not remain the case; recent research places A. atratoensis in the subgenus Poecilurichthys.[8][9] (The others remain in Zygogaster.) In 1917, Eigenmann also remarked upon the close relationship between A. caucanus and A. stilbe.[10]
The genus name "Astyanax" is an allusion to the Iliad, a Greek epic poem in which Astyanax was the son of Trojan prince Hector. The reasoning behind this was not made clear in the nominal text, but modern etymologists suspect that the appearance of type species Astyanax argentatus may be responsible; its scales are large and silvery, perhaps comparable to armor or a shield. The subgenus name "Zygogaster" originates in Greek, wherein "zygos" means pair or balanced, and "gaster" means belly, referring to the symmetrical scales on either side of the ventral midline. The specific epithet "caucanus" refers to the Río Cauca, Colombia, which is the type locality of the species.[11]
Astyanax caucanus lacks a common name.[12] "Cauca tetra" has been suggested based on the type locality and specific name.
Description
Collected specimens of A. caucanus range from 3.6 to 17.0 cm (1.4–6.7 in) standard length (SL, without the tail fin). There are 11 rays in the dorsal fin, 36–41 rays in the anal fin (most often 38), and 36–42 scales in the lateral line (most often 38).[10] There are 7 or 8 scale rows both above and below the lateral line. When compared with congeners A. filiferus and A. magdalenae from the same subgenus, A. caucanus presents with a somewhat more generalized morphology, while the other two are more specialized for their environments.[6] Sexual dimorphism is unknown.
Astyanax caucanus bears a strong resemblance to congener Astyanax atratoensis, and the shared features include coloration. A. caucanus is an iridescent silver with a slightly darker back and a lateral stripe in a lighter silver; this lateral stripe starts at a vertically elongate humeral spot and ends at a blotch of pigment on the caudal peduncle.[7] When preserved in alcohol, the scales are largely light-brown and the fins are paler than the body. The lateral stripe remains silvery, and the eye turns a silvery brown.[13]