Bryconops vibex

Bryconops vibex reaches a maximum of roughly 6.8 cm (2.8 inches) in standard length (excluding the tail fin).[2] This makes it one of the smaller members of the genus Bryconops by a thin margin, though most Bryconops are of comparable length (within ~3cm).[3] The fins are dark-tinted but translucent, and the dorsal half of its caudal fin sports an orange or yellowish ocellus (eyespot).[4] Its scales are silver to silver-green in life, which is not uncommon in the genus, and it bears a single humeral spot by each pectoral fin.[5]

Bryconops vibex is similar to many species in the genus, but there are ways to tell it apart. Its single humeral spot can be used to differentiate it from congeners like B. munduruku and B. inpai, both of which have two humeral spots,[6] or from the likes of B. affinis and B. giacopinii, which have none.[7] Its body is shallower than that of B. cyrtogaster (though still robust),[8] and small factors like a thicker caudal peduncle and a higher number of scales beneath the lateral line differentiate it from sister species B. humeralis.[9]

Along with ten other species, B. vibex is in the subgenus Creatochanes, making its full name Bryconops (Creatochanes) vibex.[6] It has been considered a member of Bryconops since its description in 1996.[9] The specific name "vibex" is Latin for "mark", referring to the humeral spot;[10] this was of note when B. humeralis and B. vibex were first described, as it was thought that B. inpai was the only other species in the genus to sport any kind of humeral spot at all.[9]

The genus Bryconops as a whole was once considered a member of the family Characidae, which is highly variable and has many genera incertae sedis. However, an in-depth study in 2011 determined by way of phylogeny that Bryconops, along with the genera Iguanodectes and Piabucus, should occupy their own family, Iguanodectidae.[11] (Iguanodectes and Piabucus make up the subfamily Iguanodectinae, while the genus Bryconops is its own monophyletic clade.)[12]

B. vibex was originally described from the Orinoco basin, in Venezuela's Amazonas state, wherein it is relatively common.[9] Specifically, it is known from the Rio Cataniapo, which is a tributary of the Rio Orinoco.[1][2] The Cataniapo is a somewhat acidic clearwater river, with a pH that ranges from 5.0 to 6.9.[13]

B. vibex has not been the subject of diet-specific study. Based on the habits of other species of Bryconops, however, it is most likely to be an˜ invertivore or an omnivore.[14][15]