Synonyms
Nannostomus marginatus picturatus Hoedeman, 1954
Etymology
The name “Nannostomus” is derived from the Latin word “nannus”, which means “small”, and the Greek word “stoma”, which means “mouth”. This name refers to the small mouthparts of the species belonging to this genus.
The species name “marginatus” is also derived from Latin, meaning “with a distinct margin, marginated”.
Classification
- Order: Characiformes
- Family: Lebiasinidae
Distribution
The type locality of the species is “Maduni Creek, Guyana”, and it can be found in many areas throughout Guyana and Suriname, as well as the middle-to-lower Amazon basin on the eastern side of the Andes mountains in Peru, Colombia, and Brazil.
It has been recorded in various major river systems, including the Rupununi, Takutu, Essequibo, and Demerara rivers in Guyana, the Nickerie and Courantyne/Corantijn rivers in Suriname, and the Inírida and Caquetá rivers in Colombia. In Peru, it has been found in the Ucayali, Javari, Ampiyacu, and Putumayo rivers, and in Ecuador and Peru, it has been recorded in the Napo River.
In Brazil, it is present in the Juruá River and throughout most major left-bank tributaries of the Amazon, including the Japurá, Negro, Branco, and Trombetas rivers. There have also been reports of its presence in the upper Río Orinoco in Venezuela, but these require further confirmation.
There are minor differences in color pattern between populations of Nannostomus marginatus. For example, some forms found in Peru have yellow pigmentation on the body and fins, while those from Guyana and Suriname possess a short red stripe on vertical scale rows 6-9, above the central dark stripe on the body.
Forms from the Rio Negro have a similar red stripe, but it overlaps with the central dark stripe and extends along most of the flank. A form from Colombia has an elongated red stripe, which is broken in two beneath the dorsal fin. One form from Peru was described as a subspecies, N. m. picturatus, by Hoedeman (1954), but it is currently considered synonymous with N. marginatus. This subspecies has a distinctive red blotch on the caudal-fin base, between the primary and secondary dark lateral stripes. However, the variability of these color patterns has yet to be studied in depth.
Habitat
The N. marginatus fish species typically inhabits slow-moving tributaries, small rivers, and swampy areas that are characterized by dense growth of aquatic vegetation, submerged woody structures, and leaf litter. They are commonly found in areas with flooded forests and floodplain lakes in blackwater regions. Their habitats are shallow, near-still water with little detectable hardness, low conductivity, and a pH range of 4.0-6.0. In these habitats, other small characids, lebiasinids, and dwarf cichlids of the genus Apistogramma can also be found.
One such habitat is La Arenosa, a small stream in Amazonas department, southern Colombia. The stream flows down from terra firme forest into a floodplain of the Amazon mainstream. It ranges from 2-5 m in width and up to 2 m in depth, and it contains slowly-moving, clear blackwater for most of the time. However, after storms, the depth and flow rate of the stream temporarily increase. The pH ranges from 5.51-6.01, conductivity is between 18-38 µS/cm, dissolved oxygen levels are at 70%, and the average water temperature is 25°C/77°F.
A study conducted over a period of one year found that N. marginatus was a permanent resident of La Arenosa stream. Symaptric species, including the congener N. trifasciatus, Axelrodia stigmatias, Hemigrammus analis, H. bellottii, H. ocellifer, H. schmardae, H. copelandi, Moenkhausia comma, M. sanctafilomenae, Tyttocharax cochui, Tetragonopterus argenteus, Characidium zebra, Crenuchus spilurus, Hoplias malabaricus, Carnegiella strigata, Copella nattereri, Corydoras semiaquilis, Megalechis thoracata, Limatulichthys griseus, Farlowella amazona, Eigenmannia virescens, Aequidens diadema, Apistogramma bitaeniata, Satanoperca sp., Cichla monoculus, Crenicichla saxatilis, and Monocirrhus polyacanthus were also present in the same habitat.
Maximum Standard Length
20 – 25 mm.
Aquarium Size
Base dimensions of at least 45 ∗ 30 cm or equivalent are necessary.
Maintenance
Ideally, this species should be kept in an aquarium that is heavily planted, with a dark substrate. This type of setup allows for broken lines of sight, which is beneficial for displaying natural behavior while reducing skittishness.
In addition to the plants, floating plants can be a useful addition to the aquarium, as well as driftwood branches and dried leaf litter. The latter, in particular, can help drive the establishment of microbe colonies as decomposition occurs. These microorganisms can provide a valuable secondary food source for fry. Furthermore, the tannins and other chemicals released by the decaying leaves are also thought to be beneficial to the aquarium’s ecosystem.
To maintain a healthy environment for this species, use gentle filtration. An air-powered sponge-style unit should be adequate in most cases. This species requires stable water conditions and should never be added to an immature aquarium. Therefore, it is crucial to establish a stable and mature aquarium before introducing this species.
Water Conditions
- Temperature: 22 – 28 °C
- pH: 4.0 – 7.0
- Hardness: 18 – 179 ppm
Diet
In its natural habitat, this species is a micropredator, feeding on tiny invertebrates and zooplankton. However, in an aquarium environment, it can adapt to consuming dried foods of a suitable size. It is essential to note that despite this adaptation, the species should still be offered daily meals of small live and frozen food such as Artemia nauplii, Moina, and grindal worm.
Offering a variety of live and frozen foods is crucial to the species’ overall health and well-being. These foods provide essential nutrients that may not be present in dried foods. Therefore, it is recommended to include live and frozen food in the species’ regular feeding routine
Behaviour and Compatibility
This species is generally very peaceful, but due to its small size and timid nature, it does not make an ideal community fish. Instead, it is best kept with similarly-sized and peaceful characids, as well as smaller callichthyid or loricariid catfishes.
Moreover, it is 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 prey on fry.
This species is gregarious, and it is recommended to purchase as many individuals as possible, ideally 10 or more, as keeping them in larger groups spreads out any aggression between individuals. Additionally, the fish are bolder and exhibit more natural behavior in larger groups.
Unlike some of its relatives, rival males rarely spar or cause harm to each other in any way. Thus, it is safe to keep multiple males together in the same tank without any major concerns.
Sexual Dimorphism
There is a significant difference in body structure between adult male and female fish. The adult male fish are observed to be less stout or less bulky than the adult females. Furthermore, in a particular variety of fish found in the Rio Negro river, the male fish display a distinct physical characteristic. Specifically, the anal fin of the male fish has been modified, with the third to sixth rays of the fin being noticeably thickened. This feature is unique to the male fish and is not found in female fish of the same variety.
Reproduction
Breeding fish in a densely planted aquarium may result in small numbers of fry appearing naturally, but it is a rare occurrence. For those who wish to breed fish and have a greater yield of fry, a more controlled approach is necessary.
To begin, one or more smaller containers should be set up and filled with aged water and fine wool mops, Taxiphyllum or other fine-leaved aquatic plants. Lighting and filtration are not necessary, but a small air-powered sponge filter may be used if preferred.
The adult fish can still be conditioned together, but when they are well-conditioned, one or more pairs should be introduced to each container. It is important to note that the more individuals involved, the greater the risk of egg predation. After 2-3 days, the adult fish should be removed, and the first fry should be visible a day or two later.
Another effective method when using mops is to check them daily, removing and replacing them as eggs are found and hatching the fry elsewhere.
To ensure the healthy development of the fry, the initial food should be Paramecium or a proprietary dry food of sufficiently small (5-50 micron) grade. As the fry grow and develop, they can be introduced to Artemia nauplii, microworm, and other suitable foods. Regular water changes, maintaining good water quality, and providing a suitable environment will promote the growth and development of the fry.
Notes
The species in question is a popular choice in the aquarium hobby and belongs to a group of similar species, including N. mortenthaleri and N. rubrocaudatus. These species are characterized by their short, stubby body shape and less than 23 scales in the lateral series. However, this species can be differentiated from N. mortenthaleri and N. rubrocaudatus by its lack of sexual dichromatism and its color pattern consisting of three dark lateral stripes with no reddish or purple color between them in males.
This species is also distinguished from all other members of the genus by possessing a relatively short anal fin that does not reach the caudal fin and lacking an adipose fin. If the fish looks different when you switch on the aquarium lights after dark or in the morning, do not worry. Like most Nannostomus species, it assumes a paler, cryptic color pattern at night, with the dark lateral stripes disappearing and two oblique bars visible posterior to the dorsal fin. This diurnal rhythm has been shown to occur in blind specimens, suggesting that it is an automatic response that the fish cannot control.
The family Lebiasinidae belongs to the order Characiformes, which is one of the most diverse orders of freshwater fishes, currently comprising close to 2000 valid species distributed among 19 families. The Lebiasinidae family is sometimes split into the nominal subfamilies Lebiasininae and Pyrrhulininae. All Lebiasinid genera possess a relatively long, elongate body shape with 17-33 scales in the lateral series, and the laterosensory canal system is absent or reduced to seven scales or less. Some species have an adipose fin, while others do not, and the anal fin has a relatively short base of 13 scales or less. In most members, males have an enlarged or well-developed anal fin used in courtship and spawning.
The frontal/parietal fontanelle is always absent, 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. However, there has not been a major review of the grouping in recent times, and the taxonomic and morphological diversity has historically made it difficult to resolve the genetic relationships between the different genera.
Modern molecular phylogenetic techniques have provided some insight, with a research paper by Calcagnotto et al. published in 2005 revealing interesting hypotheses. Their results suggest that Lebiasinidae forms a trans-Atlantic, monophyletic clade alongside the families Ctenoluciidae and Hepsetidae, with this clade forming a sister group to Alestidae. Others, such as Oliveira et al. (2011), have concluded that the family Erythrinidae is also closely related to this grouping, with Hepsetidae and Alestidae being more distant.
References
- Eigenmann, C. H., 1909 – Annals of the Carnegie Museum 6(1): 4-54
Reports on the expedition to British Guiana of the Indiana University and the Carnegie Museum, 1908. Report no. 1. Some new genera and species of fishes from British Guiana. - Arbeláez, F., G. Gálvis, J. I. Mojica, and S. Duque, 2004 – Amazoniana 18(1/2): 95-107
Composition and richness of the ichthyofauna in a terra firme forest stream of the Colombian Amazonia. - 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., 1966 – Proceedings of the United States National Museum v. 119 (no. 3538): 1-56
Review of South American characid fishes of subtribe Nannostomina. - 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). - Zarske, A., 2009 – Vertebrate Zoology 59(1): 11-23
Nannostomus rubrocaudatus sp. n. – ein neuer Ziersalmler aus Peru (Teleostei: Characiformes: Lebiasinidae).
