- Poeciliobrycon eques (Steindachner, 1876);
- Poeciliobrycon auratus Eigenmann, 1909
The genus name “Nannostomus” is made up of two separate words – “nannus” and “stoma.” “Nannus” is a Latin word that means “small,” while “stoma” is a Greek word that means “mouth.” Therefore, the name “Nannostomus” is a combination of these two words and is used to describe the small size of the mouthparts of the various species within this genus.
On the other hand, the name “eques” has Latin roots and means “knight,” “horseman,” or “rider.” This name was chosen for a specific species within the Nannostomus genus. The reason behind this choice was that this particular species is known to swim at an oblique angle that is similar to a knight riding a horse. Therefore, the name “eques” is used to describe this species’ unique swimming behavior.
- Order: Characiformes
- Family: Lebiasinidae
This species was initially discovered in the Peruvian Amazon, in the Três Fronteiras region of Amazonas state, which is located above Tabatinga. Tabatinga is a town located in northwestern Brazil where the borders of Brazil, Peru, and Colombia meet. After its discovery, the species was found in many other areas throughout the central and upper Amazon region in Brazil, Peru, and Colombia. It has been recorded in various rivers, including the rios Tapajós, Trombetas, Madeira, Negro, Japurá, Içá, and Putumayo. It is also known to exist in the Orinoco drainage in Venezuela and Colombia, specifically in the Guaviare and Inírida tributary systems, as well as in various rivers in Guyana, including the Essequibo and Curuni.
Genetic research has been conducted on populations of the species found in different regions, revealing some interesting findings. For instance, populations found in the upper and middle/lower Rio Negro in Brazil were found to be separate evolutionary units. They do not hybridize, even when they occur sympatrically in the same locality, such as in the Igarapé Jacuná, a tributary of the middle Negro. Although these populations may appear identical, they are more closely related to the congener N. unifasciatus than to N. eques populations found in the upper Negro. These findings raise the possibility that the species as currently recognized may represent a complex of reproductively-isolated cryptic taxa. This genetic research has provided us with a deeper understanding of the species and its evolution across different populations and locations in South America.
The groups is known to inhabit slow-moving tributaries, small rivers, and swampy areas. It is commonly found in regions where aquatic vegetation grows densely or where submerged woody structures and leaf litter are present. It prefers areas of flooded forests and floodplain lakes in blackwater regions.
One example of a typical blackwater habitat where this species has been observed is a small rivulet of the lower Río Atabapo in Colombia. Here, the water is clear, acidic, and tea-colored, with a pH of 4.4 and a conductivity of 10 µS/cm. The water’s total and temporary hardness are both less than 1°dH, and the water temperature is 24.4°C/75.9°F. In this habitat, this species is found in shallow water of 10-50 cm depth among submerged terrestrial vegetation.
This kind of fish coexists with several other sympatric species in the same habitat, including Dicrossus gladicauda, Hemigrammus bleheri, Hyphessobrycon stictus, Paracheirodon axelrodi, Copella meinkeni, and Apistogramma uapesi. In slightly deeper water, Mesonauta insignis and Biotodoma wavrini have also been observed. These observations provide valuable information about the ecological niche of this species and its coexistence with other species in its habitat.
Maximum Standard Length
The Maximum Standard Length of this fish is reported to be between 25 and 35 mm. This measurement refers to the length of the fish from the tip of its snout to the end of its tail fin, with the fins compressed against the body.
It is important to note that this maximum length may vary depending on a variety of factors, including the specific species of fish, its age, and its environment. Additionally, measuring the length of a fish can be challenging, as it requires the fish to be still and properly positioned.
Knowing the maximum standard length of a fish is important in order to properly care for it in captivity and to understand its natural behaviors in the wild. It is also a useful metric for researchers studying the fish, as it can provide insight into the species’ growth patterns and size distribution in a given population.
To house this fish in an aquarium, it is recommended to have a minimum base dimension of 60 x 30 cm or equivalent. This is because the fish requires a certain amount of space to move around and explore its environment.
Having an appropriately sized aquarium is essential for the fish’s health and well-being, as it provides enough room for the fish to swim and exercise. Additionally, a larger aquarium can help to maintain stable water conditions, as it provides a larger volume of water to dilute any waste produced by the fish.
It’s worth noting that the minimum recommended aquarium size is just a guideline and larger aquariums are often better. Factors such as the number of fish in the aquarium, the type of filtration system being used, and the presence of other aquatic plants or animals can all affect the necessary size of the aquarium.
Generally, an aquarium with a minimum base dimension of 60 x 30 cm or equivalent is required to house this fish. However, a larger aquarium is often preferable, as it allows the fish to thrive in a more spacious environment and helps to maintain stable water conditions.
In order to maintain this fish in captivity, it is recommended to create a heavily-planted set-up with a dark substrate. The presence of patches of floating vegetation can also be beneficial, as the fish will tend to congregate around these areas with their bodies angled towards the surface.
Adding driftwood branches and dried leaf litter to the aquarium can also be helpful in establishing microbe colonies. As the leaves decompose, they release tannins and other chemicals that are thought to be beneficial to the fish. These microorganisms can also provide a valuable secondary food source for fry.
When it comes to filtration, it is important to use a gentle system. An air-powered sponge-style unit is usually adequate for most cases, but a degree of flow is also acceptable.
In summary, maintaining this fish in captivity requires creating a suitable environment with a heavily-planted set-up and a dark substrate. Adding driftwood branches and dried leaf litter can help to establish microbe colonies and provide additional benefits. A gentle filtration system should also be used to ensure the fish’s health and well-being in the aquarium.
The water conditions necessary for this fish to thrive are specific and require careful monitoring. The recommended temperature range for the water is between 22 and 28 °C, which is relatively moderate and within the range of most tropical freshwater aquariums.
The pH level of the water should ideally be between 4.5 and 7.5, which is relatively acidic to slightly alkaline. Keeping the water within this range can help to ensure the fish’s health and well-being, as they are adapted to living in blackwater conditions.
Additionally, the water hardness level should be between 18 and 179 ppm. This is relatively soft water, and it’s important to ensure that the water remains within this range to prevent any health issues that can arise from hard water.
Maintaining the proper water conditions can be achieved through careful monitoring of the water temperature, pH, and hardness levels. Regular water testing and adjustments may be necessary to ensure that the water remains within the recommended ranges.
Overall, the recommended water conditions for this fish include a temperature range of 22-28 °C, a pH range of 4.5-7.5, and a hardness range of 18-179 ppm. Proper monitoring of the water conditions and adjustments as needed can help to ensure that the fish thrives in its environment.
This fish is a micropredator in nature, primarily feeding on tiny invertebrates and other zooplankton. When kept in an aquarium, it will typically accept dried foods of a suitable size. However, it is important to supplement its diet with daily meals of small live and frozen fare, such as Artemia nauplii, Moina, and grindal worm.
Offering a varied diet that includes live and frozen foods can help to ensure that the fish receives all the necessary nutrients for optimal health and growth. These types of foods can provide the fish with essential vitamins and minerals that may be lacking in dried foods.
It’s important to note that overfeeding can quickly lead to poor water quality and health issues for the fish. As such, it’s important to feed small, frequent meals throughout the day rather than one large meal.
In conclusion, this fish is a micropredator that primarily feeds on tiny invertebrates and other zooplankton in nature. In an aquarium, it will accept dried foods of a suitable size, but it should also be offered daily meals of small live and frozen fare, such as Artemia nauplii, Moina, and grindal worm. A varied diet can help to ensure the fish receives all necessary nutrients for optimal health, and small, frequent feedings are preferable to one large meal.
Behaviour and Compatibility
This species is generally considered to be a very peaceful species, but it may not be the best fit for a community aquarium due to its small size and somewhat timid nature. When kept in a community, it is best to house this fish with similarly-sized, peaceful characids and smaller callichthyid or loricariid catfishes.
This fish can also serve as an ideal dither fish for Apistogramma species and other dwarf cichlids, as it tends to inhabit the middle-to-upper regions of the tank and does not actively prey on fry.
It’s worth noting that this fish is a gregarious animal and tends to do best in groups. It is recommended to buy as many as possible, ideally 10 or more. When kept in larger groups, any aggression is spread between individuals, and the fish tend to be bolder and exhibit more natural behavior.
Unlike some of its relatives, rival males of this species rarely spar or harm each other in any way. This makes them an excellent choice for a peaceful community aquarium, especially when kept with other non-aggressive species.
In summary, this fish is generally a peaceful species that is best kept with similarly-sized, peaceful characids and smaller callichthyid or loricariid catfishes. It is an ideal dither fish for Apistogramma species and other dwarf cichlids, and tends to do best in groups of 10 or more. Rival males of this species are not aggressive towards each other, making it an excellent choice for a peaceful community aquarium.
Sexual dimorphism is observed in this fish species, where adult males are typically more colorful and slimmer than females. Additionally, males possess an enlarged anal fin, which is used during breeding to help transfer sperm to the female.
The differences in coloration and body shape between males and females can be quite noticeable, especially in well-maintained aquariums. Males may display brighter colors and more intricate patterns, while females tend to have more subdued coloration.
The enlarged anal fin of males is a distinctive feature that can help identify their sex. However, this trait may not be noticeable until the fish reach sexual maturity, which can take several months.
It is important to note that sexual dimorphism can vary between individuals and populations of this species. While the differences mentioned above are generally true for most specimens, there may be exceptions.
In conclusion, sexual dimorphism is observed in this fish species, with adult males typically displaying more vibrant colors and a slimmer body shape compared to females. Additionally, males possess an enlarged anal fin that is used during breeding. However, sexual dimorphism can vary between individuals and populations, and the differences mentioned above may not always be readily apparent.
While breeding this fish in an aquarium setting is rare, it is possible with a few controlled measures. A densely-planted, mature aquarium can create a suitable environment for the fish to breed naturally, but intervention may still be required to increase the yield of fry.
To achieve successful breeding, one or more smaller containers should be set up and filled with aged water. These containers should also have a clump or two of broad-leaved aquatic plants such as Anubias, Microsorum, or Echinodorus added to them. This species deposits its eggs in single batches on the underside of plant leaves, so these plants will provide an ideal surface for the fish to lay their eggs.
To increase the yield of fry, a slightly more controlled approach is required. The adult group can be conditioned together in a tank, but one or more smaller containers should also be set up and filled with aged water. Broad-leaved aquatic plants such as Anubias, Microsorum, or Echinodorus should be added, as this species deposits its eggs in single batches on the underside of plant leaves.
Once the adult fish are well-conditioned, a single pair or a group comprising one or two males and several females can be introduced to each container. However, it is worth noting that the more individuals involved, the greater the risk of egg predation, as this species will eat any eggs it finds. Once eggs are visible, the adults or plant itself should be removed, with a separate hatching tank required using the latter approach.
The first fry should be visible after around 24-36 hours, with the majority free-swimming by the 5th or 6th day. The initial food for the fry should be Paramecium or a proprietary dry food of sufficiently small (5-50 micron) grade. As they grow, small live or frozen foods like Artemia nauplii and microworms can be introduced.
It is worth noting that the breeding process for this fish can be challenging and may require extensive knowledge and experience. In memory of the late expert fish-breeder Alan P. Vaissiere, who assisted extensively with this section, it is important to approach breeding this species with care and attention to detail.
The taxonomic history of this fish species has been complex, and it has been referred to by different names such as Poecilobrycon and Nannobrycon in the past. In the aquarium hobby, it goes by several common names, including ‘rocket’, ‘brown’, ‘brown-tailed’, ‘diptail’, or ‘tubemouth’ pencilfish. Despite this confusion, it continues to be a popular aquarium fish due to its unusual oblique swimming style, which is only shared with N. unifasciatus among related species.
The original description of this fish, made by Steindachner, provides a detailed account of its color pattern. It includes a brown lateral stripe that extends from the snout to the base of the caudal fin. Above this dark brown stripe is a silver-grey stripe. Additionally, there is a dark brown spot on each body scale, except for those that form part of the silver stripe. It’s worth noting that the adipose fin is not always present in this species.
In contrast, a more recent diagnosis of the species was given by Weitzman in 1966. This diagnosis characterizes the species based on the following features: possession of five lateral body stripes, no perforated lateral line scales, 24-25 scales in the lateral series, 33-34 vertebrae, iii, 9 anal-fin rays, 16+24 gill rakers, and 12 teeth in the second tooth row of the dentary. These characteristics can help to identify and differentiate this species from others in the same genus.
It is worth noting that this fish assumes a cryptic, vertically-barred color pattern at night, which is common among most Nannostomus species. This diurnal rhythm appears to occur in blind specimens, suggesting it’s an automatic response that the fish cannot control.
The fish species in question belongs to the family Lebiasinidae, which is part of the order Characiformes. All genera within the family share a similar body shape, which is long and elongated, and they typically have 17-33 scales in the lateral series. The laterosensory canal system in Lebiasinidae is either absent or reduced to seven scales or less. Some species within this family possess an adipose fin, while others do not. The anal fin has a relatively short base, typically with 13 scales or less, and in most Lebiasinidae species, males have an enlarged or well-developed anal fin that they use during courtship and spawning.
The order Characiformes is one of the most diverse freshwater fish orders, with approximately 2000 valid species distributed among 19 families. However, the immense taxonomic and morphological diversity has made it challenging for researchers to determine their genetic relationships. Thanks to modern molecular phylogenetic techniques, Calcagnotto et al. published a research paper in 2005 that provided some interesting hypotheses. Their results suggest that Lebiasinidae forms a trans-Atlantic, monophyletic clade alongside the families Ctenoluciidae and Hepsetidae. This clade further forms a sister group to Alestidae. Oliveira et al. (2011) also concluded that the family Erythrinidae is closely related to this grouping, with Hepsetidae and Alestidae being more distant. These findings have helped to shed light on the genetic relationships within this diverse order.
In summary, this fish species has a complex taxonomic history, but it remains a popular aquarium fish due to its unique swimming style. It is part of the family Lebiasinidae within the order Characiformes, which is among the most diverse orders of freshwater fishes. Modern molecular phylogenetic techniques have allowed researchers to gain insights into the genetic relationships of various fish families, including Lebiasinidae.
- Steindachner, F., 1876 – Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe v. 74 (1. Abth.): 49-240
Ichthyologische Beiträge (V).
- 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.
- Ortega, H. and R. P. Vari, 1986 – Smithsonian Contributions to Zoology No. 437: iii + 1-25
Annotated checklist of the freshwater fishes of Peru.
- Terencio, M. L., C. H. Schneider, and J. I. R. Porto, 2012 – Journal of Fish Biology 81(1): 110-124
Molecular signature of the D-loop in the brown pencilfish Nannostomus eques (Characiformes, Lebiasinidae) reveals at least two evolutionary units in the Rio Negro basin, Brazi .
- 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).