Poeciliobrycon digrammus Fowler, 1913
Nannostomus: from the Latin nannus, meaning ‘small‘, and Greek stoma, meaning ‘mouth’, in reference to the small mouthparts of member species.
- Order: Characiformes
- Family: Lebiasinidae
This fish is indigenous to the central Amazon basin and has been documented in the Madeira, Branco, Trombetas, and Tapajós river systems as well as the Rupununi basin in Guyana.
Despite not being formally recognized as part of the Amazon basin due to its connection to the Rio Essequibo, the Rio Takutu, a tributary of the upper Rio Branco, links the former during the annual wet season. The type locality, as designated by Fowler, is the Rio Madeira, located around 200 miles east of W. Long. 62°20′ in Brazil. More recently, fish that closely resemble the aforementioned species, but possess an additional thin dark stripe in the lower part of their bodies (refer to ‘Notes’), have been exported from Colombia and are thought to occur in Peru as well.
Inhabits sluggish tributaries, small rivers and swampy areas, particularly in areas with dense growth of aquatic vegetation or submerged woody structures and leaf litter.
Maximum Standard Length
25 – 30 mm.
For optimal health and well-being, it is recommended to house this species in a heavily planted aquarium with a dark substrate. The natural behavior of the fish can be observed better in such a setup, as the plants create broken lines of sight and reduce their skittishness. Floating plants, driftwood branches, and dried leaf litter can also be added to the aquarium. The leaf litter, in particular, helps establish microbe colonies as decomposition occurs, providing a valuable secondary food source for fry. Moreover, the tannins and other chemicals released by the decaying leaves are thought to have beneficial effects on the fish’s health. To maintain a gentle flow of water, an air-powered sponge-style filter unit should suffice in most cases.
- Temperature: 22 – 28 °C
- pH: 5.0 – 7.0
- Hardness: 18 – 179 ppm
Behaviour and Compatibility
Despite being a peaceful species, it is not recommended to keep this fish in a community tank due to its small size and timid nature. Instead, it is best to keep them with similarly-sized, peaceful characids and smaller callichthyid or loricariid catfishes. Additionally, this fish can serve as an excellent dither fish for Apistogramma spp. and other dwarf cichlids since it tends to inhabit the middle-to-upper regions of the tank and does not actively predate fry.
Although naturally gregarious, this species is a shoaling rather than schooling fish, with rival males often sparring during daylight hours. Within a group, it is not uncommon to observe nipped fins, although this behavior usually does not extend to tank mates. It is advisable to purchase as many individuals as possible, ideally 10 or more, as when kept in larger groups, any aggression is spread between individuals, and the fish exhibit bolder and more natural behavior.
In this species, adult males have a significantly modified and elongated anal fin. Additionally, they are typically more brightly colored and have a slimmer body shape compared to females.
With nearly 2000 valid species distributed among 19 families, the order Characiformes is one of the most diverse groups of freshwater fishes. However, resolving genetic relationships between many of the genera has been challenging. Molecular phylogenetic techniques have provided some progress, as seen in a 2005 study by Calcagnotto et al., which revealed some interesting hypotheses. According to their findings, Lebiasinidae, along with the families Ctenoluciidae and Hepsetidae, form a trans-Atlantic, monophyletic clade. This clade is further a sister group to Alestidae. Other studies, such as Oliveira et al. (2011), suggest that the family Erythrinidae is also closely related to this group, with Hepsetidae and Alestidae being more distant. All lebiasinid genera share a relatively long, elongate body shape, with 17-33 scales in the lateral series, and laterosensory canal system absent or reduced to 7 scales or less. Males of the majority of species possess an enlarged or otherwise well-developed anal fin, which is used in courtship and spawning. The frontal/parietal fontanelle is absent, and the cheek is well-covered by the orbital and opercular bones. The supraoccipital crest is absent, and the scales of the dorsal body begin over the parietal bones. Some species have an adipose fin, while others do not, and the anal fin has a relatively short base of 13 scales or less
- Fowler, H. W., 1913 – Proceedings of the Academy of Natural Sciences of Philadelphia 65: 517-179
Fishes from the Madeira River, Brazil.
- Calcagnotto, D., S. A. Schaefer, and R. DeSalle, 2005 – Molecular Phylogenetics and Evolution 36(1): 135-153
Relationships among characiform fishes inferred from analysis of nuclear and mitochondrial gene sequences.
- Oliveira, C. A., G. S. Avellino, K. T. Abe, T. C. Mariguela, R. C. Benine, G. Orti, R. P. Vari, and R. M. Corrêa e Castro, 2011 – BMC Evolutionary Biology 11(1): 275-300
Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling.
- Weitzman, S. H. and J. S. Cobb, 1975 – Smithsonian Contributions to Zoology 186: i-iii + 1-36
A revision of the South American fishes of the genus Nannostomus Günther (family Lebiasinidae).