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The tailspot tetra ( Bryconops caudomaculatus) is a small species of freshwater Actinopterygii belonging to the family Iguanodectidae. This fish is found in the coastal river regions of upper South America. Both its common and scientific names reference the distinct spot of color present on the tail fin, which is one of its defining characteristics. It is a small fish, reaching 4.8 in (12.4 cm) at its longest. Despite its small size, it is an active swimmer, with a preference for fast-flowing waters.
/ref> It reaches 4.8 in (12.4 cm) in Fish measurement (with the tail fin included), and a corresponding weight of 20.1 grams. Its back scales are tinted orange to dark-orange, fading into silver on the belly when the fish is alive. Upon close inspection, the scales are also revealed to have a scattering of minute dots.
The spot of bright orange on the basal half of the caudal fin is what gives the tailspot tetra its common name. The scientific name also reflects this - "caudo-" is in reference to the caudal fin (the tail fin), and "-maculatus" means "spotted" (compare with the word "immaculate", which means "without blemishes"). Though it is more vivid in life, this spot of color may turn pale upon preservation of a given specimen.Machado-Allison, Antonio & Buckup, Paulo & Chernoff, Barry & Royero, Ramiro. (1993). Las especies del genero Bryconops Kner, 1858 en Venezuela (Teleostei, Characiformes). 14. 1-20.
Visually, the tailspot tetra is easy to confuse with congeners Bryconops magoi and B. collettei, which means that they have often been misidentified as B. caudomaculatus.Chernoff, Barry & Machado-Allison, Antonio. (2005). Bryconops magoi and Bryconops collettei (Characiformes: Characidae), two new freshwater fish species from Venezuela, with comments on B. caudomaculatus (Günther). Zootaxa. 1094. 10.11646/zootaxa.1094.1.1. (This is part of the reason they are considered to be in the same species complex.) Recent congener B. florenceae was also previously misidentified as B. caudomaculatus before its distinction as a separate species.
The lateral line is usually incomplete. Some specimens of B. caudomaculatus display a particularly truncated lateral line that makes them appear more visually similar to B. durbini. Another recently named congener, Bryconops piracolina, is visually similar, but with a difference in the lateral line - it has a smaller number of pored lateral line scales than B. caudomaculatus.
The tailspot tetra is the type species of the Bryconops caudomaculatus species complex, which includes B. caudomaculatus, B. disruptus, B. durbini, B. collettei, and B. magoi. This complex is not official, but species have been placed in it based upon Phenotype similarities and a history of synonymy with Bryconops caudomaculatus. Due to striking visual similarities and subsequent routine misidentification, B. florenceae (named in 2021) is a candidate for the complex, though this has not been professionally recognized.
The genera Bryconops, Iguanodectes, and Piabucus were previously in the family Characidae, which is incredibly variable and has many genera incertae sedis.Lima, Flávio & Malabarba, Luiz & Buckup, Paulo & Pezzi da Silva, José & Vari, Richard & Harold, Antony & Benine, Ricardo & Oyakawa, Osvaldo & Pavanelli, C. & Menezes, Naercio & Lucena, Carlos & Malabarba, Maria & Lucena, Zilda & Reis, Roberto & Langeani, Francisco & Cassati, Lilian & Bertaco, Vinicius & Moreira, Cristiano & Lucinda, Paulo. (2003). Genera incertae sedis in Characidae. In 2011, however, research by Oliveira et al. prompted the three to be moved to the family Iguanodectidae, which was revived from Eigenmann's previous work.Oliveira, C., Avelino, G.S., Abe, K.T., Mariguela, T.C., Benine, R.C., Orti, G., Vari, R.P., & Correa e Castro, R.M. (2011): Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling. BMC Evolutionary Biology, 11: 275. The tailspot tetra's classification as a Characiformes fish in the family Iguanodectidae is its current accepted position.
A study in January 2022 tested the effects of Aluminium in the tailspot tetra's environment, as aluminum is soluble in acidic waters and has been linked to Cardiotoxicity after prolonged exposure. Researchers determined that an aluminum concentration of 3.0 mg/L has a high likelihood of leading to an atrioventricular block in B. caudomaculatus, meaning that the heart's ability to beat effectively gets compromised due to interruption (blockage) of the responsible electrical impulse.
In turn, the tailspot tetra is not only a regular part of the food chain as a source for animals that eat small fish, but it is also preyed upon by Parasitism. In 2011, B. caudomaculatus was discovered to be the host for a new species of Trematoda (parasitic flatworm), Auriculostoma foliaceum (which is currently accepted as Creptotrema foliaceum).Curran, Stephen S., et al. "PHYLOGENETIC AFFINITIES OF AURICULOSTOMA (DIGENEA: ALLOCREADIIDAE), WITH DESCRIPTIONS OF TWO NEW SPECIES FROM PERU." The Journal of Parasitology, vol. 97, no. 4, 2011, pp. 661–70, http://www.jstor.org/stable/23019184. Accessed 6 Apr. 2022.
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