Carlastyanax

Carlastyanax aurocaudatus is a small species of freshwater fish in the family Characidae native to the Río Cauca in Colombia. It is the only member of the monotypic genus Carlastyanax, which was named in 1972 specifically for the species by Jacques Géry. Upon description, it was named Astyanax aurocaudatus by Carl H. Eigenmann. There has been debate concerning whether or not the genus should be recognized, but C. aurocaudatus is currently considered a valid species.

Carlastyanax aurocaudatus
1917 illustration
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Characidae
Genus: Carlastyanax
Géry, 1972
Species:
C. aurocaudatus
Binomial name
Carlastyanax aurocaudatus
Synonyms

Astyanax aurocaudatus Eigenmann, 1913

The coloration of this species - a greenish-yellow back, a white belly, and fins that range from red to yellow - is notable for differing with the sex of the individual fish, a trait known as sexual dichromatism. Females have yellow-gold tail fins (which is where the species gets its name), and males have reddish or pinkish tail fins. Spawning occurs during various times of year in the chosen habitat of C. aurocaudatus, which is clearwater streams with organic or rocky substrate. Its range is relatively restricted, but is also home to the benthic insects and riparian plant material that make up its diet.

Taxonomy

First named by German-American ichthyologist Carl H. Eigenmann in 1913, C. aurocaudatus has undergone rigorous taxonomic evaluation to determine its generic placement. Upon its nomination, it was considered to belong to the genus Astyanax, under the name Astyanax aurocaudatus.[2]

In 1972, French ichthyologist Jacques Géry constructed a new genus for it based upon several features, including number and shape of teeth, the presence of an adipose fin, and number of gill rakers;[3] specifically, one of the more important characteristics was said to be the presence of a hooked third dentary tooth.[4] Carlastyanax was then re-synonymized with Astyanax in 2005 and 2006 by researchers, based upon morphological similarities more consistent with Astyanax than with a new genus, including the tooth.[5][6]

However, more researchers in 2013 resurrected Carlastyanax from synonymy given further differentiating features, disregarding the hooked third dentary tooth. These include four teeth on the posterior premaxillary row (vs. five in all Astyanax) and eight branched dorsal-fin rays (vs. nine).[4] A 2015 study of molecular phylogeny within the subfamily Stevardiinae (within Characidae) reaffirmed this decision.[7] Today, Carlastyanax is considered a valid genus, and C. aurocaudatus its only species.[8]

In 2017, the genus Carlastyanax was determined to be a part of a clade with genera Creagrutus and Piabina.[9]

Etymology

Carlastyanax aurocaudatus is sometimes known as the gold-tailed tetra.[1][10] In fact, its specific epithet means "gold tail"; "auro-" is "gold", and "caudatus" is "tail". The genus name "Carlastyanax" is to honor Carl H. Eigenmann and the original genus to which C. audocaudatus once belonged, Astyanax.[11]

Description

Carlastyanax aurocaudatus usually reaches a size of 6.0 cm (2.3 in) standard length (SL).[12] Larger specimens can reach 7.4 cm (2.9 in) SL.[13] The dorsal fin has 8 rays, the pelvic fin 5–6, and the anal fin 26–28.[6] The head is large, with a blunt snout, and the body is generally robust.[14] The base scale color is white ventrally, with a green-to-yellow predorsal region and a lateral stripe in silver or silver-blue. The humeral spot is usually blue, and is elongated vertically, as well as somewhat obscure.[2] The pectoral and pelvic fins are pink or red with a dark margin. The other fins are different colors depending on whether the individual specimen is female or male.[5]

One species, Bryconamericus pectinatus, bears visual similarities to C. aurocaudatus, and was considered as a candidate for the genus upon its nomination; however, it remains in Bryconamericus.[14]

Sexual dimorphism

Male and female specimens of C. aurocaudatus bear drastic differences to each other when it comes to coloration. In males, the anal and caudal fins are reddish, as is the caudal peduncle. The dorsal fin, with a dark margin, is white or yellow at the base. In females, the anal fin and the entire caudal region are yellow or yellow-gray as opposed to red. The dorsal fin still has a dark margin, but the base is often a dark yellow instead of pale.[5] The difference in caudal-fin coloration was noted by Eigenmann in his original description ("In life the whole after part of the body and caudal peduncle golden or orange-red"), but was not recognized a sex characteristic.[2]

Outside of coloration, there are other differences. While mature males of multiple other related genera bear hooks on various fins, male specimens of C. aurocaudatus lack these hooks and instead simply have enlarged fin-rays in comparison to female specimens.[15] Males are also significantly larger.[5]

Distribution and habitat

Carlastyanax aurocaudatus has a restricted distribution, endemic solely to the upper Cauca river basin of Colombia, where it is found in various creeks and tributaries.[1] It was originally cited from the Boquia area, in the department of Quindío.[2]

Carlastyanax aurocaudatus has been described in areas with organic substrate.[16] Further, it prefers clear waters, and a substrate of combined organic materials and stone is not uncommon in places it inhabits.[2] It tends to linger close to the riverbed. Waters with a pH of 5.8–7.5 and a temperature range of 22°C–25°C appear to be its ideal habitat.[17]

Diet and ecology

More than half of the diet of C. aurocaudatus consists of insects, with aquatic larvae being the most prominent.[5] Benthic insects are also common.[18] The other portion consists of plant material, the vast majority of it allochthonous, and this proclivity for adaptability means that it does not compete with similar species that live within the same range; for instance, though other fishes may also target invertebrates, C. aurocaudatus does not consume enough for it to be of competitive concern, given its taste for food items like seeds and fruits.[19]

Regardless of food availability, spawning is estimated to occur in the wet seasons (April to May, September to October) and dry seasons (January to February).[5] Coloration of the anal and caudal fins becomes more vibrant during these stretches of time.[1]

Carlastyanax aurocaudatus has been observed living syntopically with Cetopsorhandia boquillae, Trichomycterus caliense, and Poecilia caucae.[19]

Conservation status

Carlastyanax aurocaudatus is considered a near threatened species by the IUCN. It has a relatively restricted range, and conservation challenges are largely in the form of agricultural development, which not only causes pollution but prompts deforestation (which in turn destroys the relevant riparian zones). However, it is unknown as to whether or not this is having a direct effect on the C. aurocaudatus population as a whole.[1]

References
  1. Jimenez-Segura, L.; Mojica, J.; Alonso, J. C. (2016). "Carlastyanax aurocaudatus". IUCN Red List of Threatened Species. 2016: e.T61662539A61662542. doi:10.2305/IUCN.UK.2016-1.RLTS.T61662539A61662542.en. Retrieved 8 August 2022.
  2. Eigenmann, Carl H. (March 1913). "Some Results from An Ichthyological Reconnaissance of Colombia, South America". Contributions from the Zoological Laboratory of Indiana University. 131: 26. Retrieved 4 May 2023.
  3. Géry, Jacques (1972). "Contribution à l'étude des poissons characoïdes de l'équateur: Avec une révision du genre pseudochalceus et la description d'un nouveau genre endémique du rio Cauca en Colombie". Acta Humboldtiana. 2 (2). Retrieved 4 May 2023.
  4. Mirande, Juan Marcos; Jerep, Fernando Camargo; Vanegas-Ríos, James Anyelo (2013). "Phylogenetic relationships of the enigmatic Carlastyanax aurocaudatus (Eigenmann) with remarks on the phylogeny of the Stevardiinae (Teleostei: Characidae)". Neotropical Ichthyology. 11 (4): 747–766. doi:10.1590/S1679-62252013000400003.
  5. Román-Valencia, Cesar; Ruizc, Raquel Ivveth (January 2005). "Diet and reproduction aspects of Astyanax aurocaudatus (Teleostei: Characidae) from the upper part of the rio Cauca, Colombia". Dahlia (Journal of the Colombian Society of Ichthyologists). 8: 9–17.
  6. Ruiz-C., R. I. D.; Román-Valencia, C. (30 June 2006). "Osteología de Astyanax aurocaudatus Eigenmann, 1913 (Pisces, Characidae), con notas sobre la validez de Carlastyanax Géry, 1972". Animal Biodiversity and Conservation. 29 (1): 49–64. doi:10.32800/abc.2006.29.0049. S2CID 83365736.
  7. Thomaz, Andréa T.; Arcila, Dahiana; Ortí, Guillermo; Malabarba, Luiz R. (December 2015). "Molecular phylogeny of the subfamily Stevardiinae Gill, 1858 (Characiformes: Characidae): classification and the evolution of reproductive traits". BMC Evolutionary Biology. 15 (1): 146. doi:10.1186/s12862-015-0403-4. PMC 4509481. PMID 26195030.
  8. Eschmeyer, William N.; Fricke, Ron & van der Laan, Richard (eds.). "Species in the genus Carlastyanax". Catalog of Fishes. California Academy of Sciences. Retrieved 3 May 2023.
  9. Vanegas-Ríos, James A (28 March 2018). "Phylogeny of the Neotropical genus Gephyrocharax (Characiformes: Characidae: Stevardiinae), with remarks on the tribe Stevardiini". Zoological Journal of the Linnean Society. 182 (4): 808–829. doi:10.1093/zoolinnean/zlx045.
  10. Myers, P.; Espinosa, R.; Parr, C. S.; Jones, T.; Hammond, G. S.; Dewey, T. A. "Carlastyanax aurocaudatus Gold-tailed tetra - Classification". animaldiversity.org. University of Michigan Department of Zoology. Retrieved 4 May 2023.
  11. Scharpf, Christopher; Lazara, Kenneth J. (29 December 2022). "Order CHARACIFORMES: Family CHARACIDAE: Subfamily STEVARDIINAE + Incertae sedis". The ETYFish Project. Retrieved 3 May 2023.
  12. Reis, Roberto E.; Kullander, Sven O.; Ferraris, jr, Carl J. (January 2003). "Genera incertae sedis in Characidae". Checklist of the Freshwater Fishes of South and Central America: 120.
  13. Trujillo Jiménez, Patricia; Sedeño Díaz, Jacinto Elias; Camargo, Julio A.; López López, Eugenia (24 July 2013). "Reproductive traits and population structure of Astyanax aeneus (Characiformes: Characidae) from a subtropical river in Mexico". Revista de Biología Tropical. 61 (2): 769–786. doi:10.15517/rbt.v61i2.11221. PMID 23885588.
  14. Siebert, Darrell J.; Vari, Richard P. (1990). "A new, unusually sexually dimorphic species of Bryconamericus (Pisces: Ostariophysi: Characidae) from the Peruvian Amazon". Proceedings of the Biological Society of Washington. 103: 516–524. Retrieved 4 May 2023.
  15. "Comunicações do Museu de Ciências e Tecnologia da PUCRS". Pontifícia Universidade Católica do Rio Grande do Sul. Museu de Ciências e Tecnologia: 76. 2002. Retrieved 4 May 2023.
  16. "Clave Taxonomica Gephyrocharax [Uncertain]". Cespedesia. Departamento del Valle del Cauca. 22 (69). 1997. Retrieved 4 May 2023.
  17. Froese, Rainer; Pauly, Daniel (eds.) (2023). "Astyanax aurocaudatus" in FishBase. May 2023 version.
  18. Román-P., Cristian; Román-Valencia, César; Taphorn, Donald C. (15 January 2015). "Trophic and Reproductive Ecology of a Neotropical Characid Fish Hemibrycon Brevispini (Teleostei: Characiformes)". Caldasia. 36 (2): 289–304. doi:10.15446/caldasia.v36n2.47487.
  19. Román Valencia, César; Bottero, Alvaro (2006). "Trophic and reproductive ecology of a species of Hemibrycon (Pisces: Characidae) in Tinajas creek, Quindío River drainage, upper Cauca basin, Colombia". Revista del Museo Argentino de Ciencias Naturales. 8: 1–8. doi:10.22179/REVMACN.8.359.
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