Bryconops tocantinensis
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| Bryconops tocantinensis | |
|---|---|
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Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Iguanodectidae |
| Genus: | Bryconops |
| Species: | B. tocantinensis |
| Binomial name | |
| Bryconops tocantinensis | |
Bryconops tocantinensis is a species of freshwater ray-finned fish belonging to the family Iguanodectidae. This species is found in Brazil. It has yellow-gold scales on its back and white scales on its belly, with a bright-silver stripe marking the divide between the two. It gets the name "tocantinensis" from its endemism to the upper Tocantins basin drainage - specifically, the Conceição River.
Sexual dimorphism
Bryconops tocantinensis reaches about 6.5 cm (2.6 in) in standard length (excluding the tail fin),[1] which makes it one of the smaller members of the genus.[2] The dorsal, adipose, and caudal fins are all entirely orange, which is a similarity it shares only with congeners B. humeralis and B. vibex.[3] However, it can easily be distinguished from the two because it lacks humeral spots (whereas the others have one on each side) and because it lacks teeth on the maxilla (vs. 1-3 on each side).[4]
The scales on the upper half of the body are a yellow-gold color, with a bright silver lateral stripe marking the divide; the lower half is white-to-silver.[4] The upper portion of the face and head is slightly darker, as are the distal portions of both lobes of the caudal fin.[3] It has 38 to 48 pored lateral line scales; these scales are easily visible, and can be used to distinguish B. tocantinensis from congeners B. vibex and B. rheoruber.[1][5]
Bryconops tocantinensis demonstrates sexual dimorphism in that mature males sport bony hooks on the rays of the anal and pelvic fins.[4] (This is also seen in other members of Bryconops.)[6] Otherwise, they are very morphologically similar to one another, including in coloration (with the exception that larger females may have some orange near the pectoral fin).[3] This includes both in life and when preserved in alcohol.
Taxonomy
Since its description in 2016, B. tocantinensis has been considered a member of the subgenus Bryconops due to the lack of teeth on its maxillaries.[3] There are nine other species classified as such alongside it.[5] The other subgenus in Bryconops, Creatochanes, is characterized by having 1 to 3 teeth on either side of the maxillary.[7]
Habitat and distribution
Bryconops tocantinensis is known only from the rio Conceição, a tributary of the rio Palma, which is a part of the upper rio Tocantins drainage.[3] The specific epithet "tocantinensis" is in reference to this.[8] (The suffix -ensis denotes being found in a specific location; compare Lynx canadensis, the Canada lynx, or Callopistria floridensis, the Florida fern moth.)
The Rio Conceição itself is a clearwater river with a depth of up to 1.5 m (5 ft).[4] The substrate is a mixture of sand and stones.[3] There is adequate riparian vegetation, largely in the form of trees and shrubs.[4]