Iguanodectes gracilis

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Iguanodectes gracilis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Iguanodectidae
Genus: Iguanodectes
Species:
I. gracilis
Binomial name
Iguanodectes gracilis
Géry, 1993

Iguanodectes gracilis is a small species of freshwater fish from South America. It is known solely from the Rio Negro river system, which restricts its range only to Brazil. The name "gracilis" is in reference to a slender body shape, alongside the diminutive nature of I. gracilis - it is the smallest member of the genus Iguanodectes.

Granted species status in 1993, I. gracilis is one of the more recent additions to the genus Iguanodectes. The publication that described it also described congeners I. variatus and I. polylepis, both of which are generally more well-studied.

Description[edit]

Iguanodectes gracilis is a small species, reaching a maximum of 4.6 cm (1.8 in) standard length (SL).[1] As with all Iguanodectinae, I. gracilis has a compressed, elongate body, comparable to the general shape of a smelt or minnow.[2][3] When compared to congeners, however, it is slightly more slender, and is the smallest of the genus.[4] (The largest is Iguanodectes variatus, which reaches 10.3 cm (4.1 in) SL.)[5]

Iguanodectes gracilis bears the greatest resemblance to congener I. adujai, with generally similar coloration aside from the fins; this includes a prominent lateral stripe on a yellowish base body color. (In all Iguanodectes, the lateral line is complete.)[3] The fins are largely hyaline, lacking any marking aside from dark pigmentation in the median caudal rays and some scattered chromatophores (color cells) on the base of the anal fin. This is unusual in Iguanodectes, and can be used to tell it apart from several congeners.[6]

All members of the subfamily Iguanodectinae, including Iguanodectes, are equipped with multicuspid teeth. This is a feature shared with sister clade Bryconops.[7] Iguanodectes as a genus is also generally shallow-chested, lacking the pectoral keel seen in sister genus Piabucus, but I. gracilis specifically is somewhat deep-bodied for an iguanodectid.[6][8]

Taxonomy[edit]

Iguanodectes gracilis has retained its original name since designation in 1993.[9] However, it went from a member of family Characidae to family Iguanodectidae upon research in 2011 that prompted this change for the genera Iguanodectes, Piabucus, and Bryconops.[10] Iguanodectes and Piabucus make up subfamily Iguanodectinae, while Bryconops makes up a monotypic clade.[11]

Iguanodectes gracilis was first described in the same study that named Iguanodectes variatus. (This was a simultaneous publication of the smallest and largest members of the genus, respectively.) This same paper also named Iguanodectes polylepis.[6]

Etymology[edit]

The specific epithet "gracilis" means "slender" (compare the word "graceful"). This refers to the slender shape and small size of I. gracilis. The generic name "iguanodectes" likely comes from "iguana", the lizard, and "dectes", meaning "bite" or "tooth". (The meaning was not made clear in the original text.)[4]

Distribution and habitat[edit]

Iguanodectes gracilis is known from the Rio Negro basin. This is the only habitat from which it has been cited, and it is suspected to be restricted to the region.[12][13] It has largely been observed in tributaries to the river main.[14]

The Rio Negro itself is a blackwater river, which is a slow-moving, acidic river rich in microbial activity. Said activity breaks down abundant leaf litter provided by thick riparian vegetation, which releases humic substances into the water, staining it brown.[15] Microbial activity, therefore, consumes much of the available dissolved oxygen in blackwater rivers.[16][17] I. gracilis is not negatively affected by the resultant low oxygen levels.

Diet and ecology[edit]

Species-specific research on the diet and environmental interaction of I. gracilis is lacking. Patterns seen in the rest of the genus indicate that I. gracilis is most likely herbivorous,[8] perhaps with some omnivorous traits like I. geisleri and I. adujai.[18][19] One known instance of sympatry is with Potamorrhaphis guianensis, the freshwater needlefish.[20]

Presence and behavior in aquaria[edit]

There is little knowledge of I. gracilis in captivity. Nonetheless, it has been approved by the Brazilian government for export from the country.[21] It is furthermore acknowledged by MERCOSUR Common Nomenclature (MCN), which is a system responsible for maintaining records of known names for various exports.[22]

Conservation status[edit]

Iguanodectes gracilis has not been evaluated by the IUCN.[1] Nonetheless, it inhabits wetlands in the Rio Negro basin that are under pressure from anthropogenic sources, like illegal mining and infrastructure development. Such wetlands are known for their ecological fragility, and wetland conservation efforts are frequent.[23]

References[edit]

  1. ^ a b Froese, Rainer; Pauly, Daniel (eds.) (2022). "Iguanodectes gracilis" in FishBase. December 2022 version.
  2. ^ Eigenmann, Carl H.; Meyers, George S. (1917–1929). The American Characidae. Cambridge. pp. 493–499. Retrieved 29 November 2022.
  3. ^ a b Böhlke, James E. (1954-02-01). "XV.—Studies on fishes of the family Characidae.—No. 6. A synopsis of the Iguanodectinae". Annals and Magazine of Natural History. 7 (74): 97–104. doi:10.1080/00222935408651699. ISSN 0374-5481.
  4. ^ a b Scharpf, Christopher; Lazara, Kenneth J. (15 September 2020). "Order CHARACIFORMES: Families IGUANODECTIDAE, TRIPORTHEIDAE, BRYCONIDAE, CHALCEIDAE and GASTEROPELECIDAE". The ETYFish Project. Retrieved 2 December 2022.
  5. ^ Froese, Rainer and Pauly, Daniel, eds. (2022). Species of Iguanodectes in FishBase. December 2022 version.
  6. ^ a b c Géry, J. 1993. "Description de trois espèces nouvelles du genre Iguanodectes (Pisces, Characiformes, Characidae), avec quelques données récentes sur les autres espèces." Revue française d'Aquariologie Herpétologie 19(4): 97-106.
  7. ^ Vari, Richard P. (26 January 1977). "Notes on the characoid subfamily Iguanodectinae, with a description of a new species". American Museum Novitates (2612). hdl:2246/2012 – via AMNH Digital Repository.
  8. ^ a b "THE FISH FAMILIES". Field Guide to the Fishes of the Amazon, Orinoco, and Guianas, edited by Peter van der Sleen and James S. Albert, Princeton: Princeton University Press, 2017, pp. 95-96. https://doi.org/10.1515/9781400888801-009
  9. ^ "Iguanodectes gracilis Géry, 1993". gbif.org. Global Biodiversity Information System. Retrieved 9 December 2022.
  10. ^ Oliveira, Claudio; Avelino, Gleisy S.; Abe, Kelly T.; Mariguela, Tatiane C.; Benine, Ricardo C.; Ortí, Guillermo; Vari, Richard P.; Corrêa e Castro, Ricardo M. (December 2011). "Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling". BMC Evolutionary Biology. 11 (1): 275. doi:10.1186/1471-2148-11-275. PMC 3190395. PMID 21943181. S2CID 974820.
  11. ^ Bailly, Nicolas (17 April 2015). "WoRMS taxon details - Iguanodectidae Eigenmann, 1909". World Register of Marine Species. Retrieved 8 December 2022.
  12. ^ Dagosta, Fernando C.P.; Pinna, Mário De (13 June 2019). "The Fishes of the Amazon: Distribution and Biogeographical Patterns, with a Comprehensive List of Species". Bulletin of the American Museum of Natural History. 2019 (431): 83. doi:10.1206/0003-0090.431.1.1. S2CID 196645665. Retrieved 9 December 2022.
  13. ^ van der Laan, Richard; Fricke, Ron. "adujai, Iguanodectes". Eschmeyer's Catalog of Fishes. California Academy of Sciences. Retrieved 9 December 2022.
  14. ^ Beltrão, Hélio & Zuanon, Jansen & Ferreira, Efrem. (2019). "Table S1. Checklist of the species found in the different environments of the Rio Negro basin.".
  15. ^ Weibezahn, Franz H. (1994). "Lake Guri (Venezuela): Preliminary Limnological Characterization of a Large Tropical Blackwater Reservoir". Internationale Revue der gesamten Hydrobiologie und Hydrographie. 79 (1): 47–60. doi:10.1002/iroh.19940790107. Retrieved 9 December 2022.
  16. ^ "Hypoxic blackwater events and water quality". Department of Agriculture, Water and the Environment. Australian Government. 2016. Retrieved 9 December 2022.
  17. ^ Mehring, Andrew S.; Kuehn, Kevin A.; Tant, Cynthia J.; Pringle, Catherine M.; Lowrance, R. Richard; Vellidis, George (2014). "Contribution of surface leaf-litter breakdown and forest composition to benthic oxygen demand and ecosystem respiration in a South Georgia blackwater river". Freshwater Science. 33 (2): 377–389. doi:10.1086/675507. S2CID 85315129.
  18. ^ "Iguanodectes geisleri (Red Line Lizard Tetra)". Seriously Fish. Retrieved 28 November 2022.
  19. ^ "Iguanodectes adujai — Seriously Fish". Seriously Fish. Retrieved 28 November 2022.
  20. ^ Mikolji, Ivan (1 November 2020). Fishes of the Orinoco in the Wild. Mikolji Corp. p. 40. ISBN 9781838538835. Retrieved 9 December 2022.
  21. ^ "Instrução Normativa Interministerial" (PDF). Diário Oficial da União (Federal Official Gazette) (in Portuguese). No. 3. Ministério da Pesca e Aquacultura. 3 January 2012. pp. 26–42. Retrieved 29 November 2022.
  22. ^ "NCM 0301.11.90 - Others". ncm.fazcomex.com.br. NCM. Retrieved 9 December 2022.
  23. ^ Sánchez, Carolina Obregón (12 February 2021). "Challenges in the management of Brazilian wetlands: Negro and Juruá Rivers". Aguas Amazonicas. Wildlife Conservation Society. Retrieved 29 November 2022.
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