Bryconops


Bryconops is a genus of freshwater ray-finned fish in the family Iguanodectidae from South America. It consists of small fish, all under half-a-foot long, with slender bodies and silvery scales, though there is some mild color variation. Several species can be identified by way of a humeral patch, and others have a reddish ocellus, or eyespot, on one or both lobes of the dorsal fin.
Many Bryconops prefer clearwater environments with a strong current, though some are partial to slow-moving blackwater, and several are endemic to their locale. The majority of species are from Brazil or Venezuela. Rivers and river basins that house species of Bryconops include the Tapajos, Orinoco, Tocantins, Negro, and Madeira.
Few species of Bryconops have been evaluated as far as conservation status, but most of them are believed to be low-risk species. The greatest threats to population levels come almost entirely in the form of anthropogenic hazards, including mining, dam construction, farmland settlement, and destruction of the riparian zone. Nonetheless, several species are found in areas of protected forest, which decreases some of the survival pressure.

Description

Members of Bryconops are fairly small, reaching just under half a foot at a maximum. B. durbini, the smallest, reaches SL, and B. giacopinii, the largest, reaches TL. They are slender, somewhat compressed and elongate, described as "spindle-shaped". The mouth is often terminal. Certain morphological consistencies within the genus have contributed to its accepted status as a monophyletic clade, though said monophyly remains somewhat unclear, and is largely based on shared physical traits.
Bryconops are most often silver or some shade therein, sometimes with a darker back and/or a greenish tint. Only three species - B. inpai, B. marabaixo, and B. sapezal - have a hint of blue in their scales. There is great variety in fin coloration, though they are most often some blend of hyaline, red, and dusky-gray; some species, like B. caudomaculatus bear an ocellus, or eyespot, on the dorsal lobe of the caudal fin. Other species, like B. affinis, have an ocellus on both lobes, nearly symmetrical. The only two species to have a dark dorsal fin are B. chernoffi and B. piracolina. It is uncommon, but not unheard of, for members of Bryconops to have a humeral mark, which is a spot of pigment near the dorsal fin.
The scales are cycloid, usually taller than they are wide. Most members of the genus have fairly well-defined radii on the scales; these are slightly more subdued in B. affinis. The scales of the lateral line are pored, but the number of pored scales varies wildly from species to species, anywhere from 9 to 61. Even within a single species, B. disruptus, the range is from 9 to 23. The pored scales either do or do not extend to the hypural plate, the plate that joins the fish's tail to its body, and this is a feature that can be used to tell species apart.

Taxonomy

Bryconops was long considered to belong to the family Characidae incertae sedis. It is still listed there by some resources, such as ADW and ITIS. Characidae is an enormously varied family, with many genera in a similar position. However, research in 2011 examined morphological and phylogenetic evidence, and prompted taxonomists to move Bryconops to a different family, Iguanodectidae. This was also done to keep Characidae monophyletic.
The genera Piabucus and Iguanodectes are in Iguanodectidae as well, and were also moved based on the 2011 research. Piabucus and Iguanodectes come together to make up a subfamily, Iguanodectinae; Bryconops is considered its own monophyletic clade. The family Iguanodectidae is a revival from some of the works of Carl H. Eigenmann, a prolific German-American ichthyologist.
Bryconops has two subgenera: Bryconops and Creatochanes. The latter was considered its own standalone genus before being synonymized with Bryconops and turned into a subgenus in 1999. Members of Bryconops usually have no teeth to either side of the maxillary, or a single conical tooth on one side. Creatochanes, in contrast, is characterized partially by the presence of 1-3 teeth to both sides of the maxillary. Another difference is in the length of the maxillary bone; in Bryconops, it does not reach the junction of the second and third infraorbital bones, but in Creatochanes it does. A third difference is in the ossification and denticulation of the gill rakers, which is strong in Creatochanes and poor in Bryconops. Creatochanes is the more speciose of the two.
Altogether, there are 27 recognized species in the genus Bryconops. This makes it the largest genus in its family; Iguanodectes has 8, and Piabucus has 3. It continues to grow into the 21st century, with new species having been described as recently as 2019, 2020, and 2021.

Species

Bryconops contains the following valid species:
  • Bryconops affinis
  • Bryconops alburnoides Kner, 1858
  • Bryconops allisoni C. S. de Oliveira, Canto & F. R. V. Ribeiro, 2019
  • Bryconops caudomaculatus
  • Bryconops chernoffi C. S. de Oliveira, Lima & Bogotá-Gregory, 2018
  • Bryconops colanegra Chernoff & Machado-Allison, 1999
  • Bryconops colaroja Chernoff & Machado-Allison, 1999
  • Bryconops collettei Chernoff & Machado-Allison, 2005
  • Bryconops cyrtogaster
  • Bryconops disruptus Machado-Allison & Chernoff, 1997
  • Bryconops durbini
  • Bryconops florenceae C. S. de Oliveira, Ota, Sabaj & Py-Daniel, 2021
  • Bryconops giacopinii
  • Bryconops gracilis
  • Bryconops hexalepis Guedes, E. F. de Oliveira & Lucinda, 2019
  • Bryconops humeralis Machado-Allison, Chernoff & Buckup, 1996
  • Bryconops imitator Machado-Allison & Chernoff, 2002
  • Bryconops inpai Knöppel, Junk & Géry, 1968
  • Bryconops magoi Machado-Allison & Chernoff, 2005
  • Bryconops marabaixo C. S. de Oliveira, Moreira, Lima & Py-Daniel, 2020
  • Bryconops melanurus
  • Bryconops munduruku C. S. de Oliveira, Canto & F. R. V. Ribeiro, 2015
  • Bryconops piracolina Wingert & L. R. Malabarba, 2011
  • Bryconops rheoruber C. S. de Oliveira, Ota, Sabaj & Py-Daniel, 2019
  • Bryconops sapezal Wingert, Chuctaya & Malabarba, 2018
  • Bryconops tocantinensis Guedes, E. F. de Oliveira & Lucinda, 2016
  • Bryconops transitoria
  • Bryconops vibex Machado-Allison, Chernoff & Buckup, 1996

    History

Upon describing Bryconops alburnoides in 1858, Austrian ichthyologist Rudolf Kner established Bryconops as a new genus. Kner also offered a description of new congener B. lucidus, which has since been synonymized with B. alburnoides. In 1910, German-American ichthyologist Carl H. Eigenmann designated Bryconops alburnoides the type species of the genus. Technically, the earliest member of the genus to be described is Bryconops melanurus, which was originally classified as Salmo melanurus by German naturalist Marcus Elieser Bloch in the year 1764.

Etymology

The genus name Bryconops originates from the genus Brycon and the Greek suffix "-ops", which means "appearance" or "resemblance". This is because Kner noted visual similarities between members of the two genera upon description. In turn, the genus name Brycon originates from the Greek "bryko", which means "to bite" or "to devour". Fish of the genus Brycon are equipped with a full set of teeth on their maxillaries, making for an apt name.
Many of the specific names in Bryconops originate with aspects of the species' appearances. For instance, "caudomaculatus" means "tail spot", for the distinct caudal ocellus on B. caudomaculatus. Other epithets originate in specific people, such as B. allisoni, B. chernoffi, and B. magoi. A few species are named after specific locations, such as B. tocantinensis, which earned its specific epithet from its likely restriction to the upper Tocantins basin. Another example is B. sapezal, from its type locale of the Sapezal municipality in Brazil. Some species names take after cultural or historical significance from the type locality, like B. munduruku, after an indigenous tribe, or B. marabaixo, after a religious and historical festival of the same name.

Habitat and distribution

All members of Bryconops are restricted to the northern half of South America, where they occupy various river basins and tributaries of major rivers. Their distribution is quite wide as a genus, though individual species display some endemism. Specific rivers known to host various species of Bryconops include the Tapajós, Orinoco, Negro, Casiquiare, and Madeira.
Members of Bryconops have varying preferences when it comes to specific environments, though they generally fall into one of two categories - those that inhabit blackwater, and those that inhabit fast-moving clearwater. Examples of the former include B. disruptus, B. humeralis, and B. colaroja. Examples of the latter include B. rheoruber, B. sapezal, and B. florenceae. Several members are found in both environments despite the contrast, such as B. collettei and B. caudomaculatus.
The lattermost species, B. caudomaculatus, demonstrates varying body composition based upon where it lives. Examination based upon physical aspects can correctly classify at least 75% of any given specimens' habitats. More of the body weight is shifted backwards for tailspot tetras that live in lagoon habitats, and the mouth is slightly more upturned for channel-dwelling tetras. It is unknown if similar morphology changes affect other members of the genus.