Bryconops Cyrtogaster

''Bryconops cyrtogaster'' is a midsize species of freshwater fish found in the rivers of South America. It is overall silver, with an indistinct dark patch at the base of the tail fin that spreads onto the fin rays slightly. Originally described in 1926 under a different baisonym, it was the subject of a redescription in June 2020.

Description

''Bryconops cyrtogaster'' is about 12 cm (4.7 in) in total length, which makes it slightly longer than the average member of its genus. Its scales are generally silver, with a faint lateral line towards its back half. One of its identifying features is a diffuse dark patch on the caudal peduncle that bleeds into the upper lobe of the caudal fin. It also has a single humeral spot above each pectoral fin.

The snout is short and the eye wide in comparison, the latter larger than the former. The mouth itself is terminal, equipped with multicuspid teeth (a feature seen in all members of ''Bryconops'', as well as sister clade Iguanodectinae). The origin of the dorsal fin is slightly closer to the caudal fin than to the tip of the snout.

''Bryconops cyrtogaster'' bears several morphological similarities to other members of the genus. It shares the presence of a single humeral patch with congeners '' Bryconops humeralis'', '' Bryconops vibex'', and '' Bryconops marabaixo'', but can be differentiated from the former two by a deeper body and a humeral spot located slightly farther back on the body. B''. marabaixo'' has fewer predorsal scales and a shorter maxillary than ''B. cyrtogaster''. Overall, ''B. cyrtogaster'' bears the greatest similarity to ''B. marabaixo'', ''Bryconops inpai'', and '' Bryconops munduruku''.

Until 2020, ''Bryconops cyrtogaster'' was generally poorly studied, but received a redescription by Silva-Oliveira et al. in June of that year. The same study that cemented its characteristics also named similar congener ''B. marabaixo''.

Taxonomy

When first described by English ichthyologist John Roxborough Norman in 1926, ''Bryconops cyrtogaster'' was listed under the original name ''Creatochanes cyrtogaster'', and has undergone several classification changes since. Knöppel et al. identified ''Bryconops cyrtogaster'' as a subspecies of '' Bryconops melanurus'' in 1968, dubbing it ''Bryconops (Creatochanes) melanurus cyrtogaster''. Chernoff et al. further simplified this designation, considering ''B. cyrtogaster'' a synonym of ''B. melanurus''. Finally, Silva-Oliveira et al. considered ''Bryconops cyrtogaster'' an independent species in 2018.

Though its taxonomy has since been studied more closely and subsequently changed, Norman's original placement for ''Bryconops cyrtogaster'' retains an element of validity. ''B. cyrtogaster'' is considered a part of the subgenus ''Creatochanes'', making its full scientific name ''Bryconops (Creatochanes) cyrtogaster''. The specific epithet ""cyrtogaster" means "curved belly", but ''B. cyrtogaster'' lacks an accepted common name.

The genus ''Bryconops'' as a whole was once considered a member of the family Characidae, but has since been reclassified as a member of the family Iguanodectidae.Oliveira, C., Avelino, G.S., Abe, K.T. et al. ()26 September 2011). Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling. ''BMC Evol Biol''. 11(275). https://doi.org/10.1186/1471-2148-11-275. Retrieved 3 May 2022. Some sources, such as Animal Diversity Web and ITIS, still list it under Characidae, but the current accepted standing of ''Bryconops cyrtogaster'' is as an Iguanodectid fish.

Habitat and ecology

''Bryconops cyrtogaster'' is only known from the Oyapock river (between French Guiana and Brazil), and this has been the case ever since its discovery. It demonstrates a preference for rocky or sandy substrate, as well as fast-flowing and well-oxygenated water, such as where waterfalls intersect with the current.

Conservation status

''Bryconops cyrtogaster'' has not been evaluated by the IUCN. The Oyapock river is not the subject of extensive development, but has a history of gold mining, which raises the amount of pollutants - specifically mercury - in the water. However, regions of a high flow or with a sandy substrate have a lower mercury content, meaning that ''B. cyrtogaster's'' preferred environment shields it from potential mercury toxicity. The Oyapock river's spread of 28000 km² offers B. cyrtogaster a relatively wide native range, meaning that it is unlikely to be at risk for extinction.

''Bryconops cyrtogaster'' is likely taken from the wild for use in the aquarium industry, but details are sparse.Prang, Gregory. (2007)
An industry analysis of the freshwater ornamental fishery with particular reference to the supply of Brazilian freshwater ornamentals to the UK market
Uakari. 3. 10.31420/uakari.v3i1.18.

References

{{Taxonbar, from=Q6417113

Fish described in 1926
Characiformes
Fish of South America
Taxa named by John Roxborough Norman