In 1909, C.H. Eigenmann created the genus Carnegiella for the species C. strigata, which was previously known as Gasteropelecus strigatus. The name “Carnegiella” was chosen in honor of Miss Margaret Carnegie and reflects the elegant nature of these fish.
- Order: Characiformes
- Family: Gasteropelecidae
The type locality for this species is located in Caño de Quiribana near Caicara, Venezuela. However, it is believed that this species can be found throughout the upper Orinoco drainage in Venezuela and the rio Negro drainage in Amazonian Brazil, with occasional specimens being recorded from the rio Madeira, which is located downstream from the mouth of the Negro on the opposite bank. There have also been records of this species in Colombia, with at least one record from the Río Vichada and another from the Río Inírida, both of which are tributaries of the Orinoco.
Although it is possible that this species may have a more restricted distribution, research published by Piggott et al. (2011) suggests the existence of at least three species in the Rio Negro basin alone.
It appears that the fish species, known as Carnegiella marthae, is adapted to living in blackwater environments. Specifically, it can be found in the rio Negro system, where it inhabits igapó and igarapé habitats. These habitats are characterized by thick, overhanging riparian vegetation, and substrates covered in fallen branches, tree roots, and leaf litter.
The water in these habitats is typically acidic, with a low carbonate hardness and conductivity. Additionally, the water is stained brownish due to the presence of humic substances that are released by decomposing organic matter. The rio Negro has a substantial floodplain, and during the annual wet season, the water level can rise by up to 15 meters.
During the period of inundation, small fishes like the Carnegiella marthae move upstream within the river’s tributaries and then laterally into the flooded forest itself to feed and reproduce. When the water level falls, they return to the tributaries. This behavior suggests that Carnegiella marthae is well-adapted to the seasonal fluctuations of the rio Negro’s floodplain.
In conclusion, Carnegiella marthae is a fish species that is adapted to living in blackwater environments. Its ability to move between different habitats during the wet season shows that it is well-adapted to the seasonal fluctuations of its environment.
Maximum Standard Length
The specimen that holds the official record for being the largest measures 28.1 mm in length.
It is recommended that the surface dimensions for keeping this species should be 60 * 30 cm or larger. This is because it is best to maintain this species in groups, as explained in the ‘Behaviour and Compatibility’ section.
It is recommended that this species be kept in a heavily-planted aquarium with a dark substrate, and patches of floating vegetation. They tend to spend most of their time at or towards the surface, and these plants provide them with the necessary shelter and hiding places.
In addition to plants, driftwood branches and dried leaf litter can also be added. These items will encourage the establishment of microbe colonies as decomposition occurs. Such microorganisms can provide a valuable secondary food source for fry, while the tannins and other chemicals released by the decaying leaves are also thought to be beneficial.
Water movement should be gentle to moderate. Also, it is important to ensure that the aquarium cover is tightly-fitted as this species may jump when startled. Overall, a well-planted and appropriately decorated aquarium is essential for the health and well-being of this species.
- Temperature: 20 – 28 °C
- pH: 4.0 – 7.0
- Hardness: 18 – 179 ppm
In its natural habitat, this species primarily feeds on terrestrial and aquatic invertebrates and other zooplankton that are found at or near the water surface. As for their diet in the aquarium, they will accept dried foods of a suitable size, but it is essential to offer them regular meals of small live and frozen fare such as Artemia nauplii, Daphnia, Moina, and grindal worm.
Small insects such as young crickets or Drosophila fruit flies are also suitable to use, although it is best to fill their stomachs by feeding them fish flakes or some kind of vegetable matter before offering them to the fish. Providing a varied diet is essential to maintain their health and promote their natural behavior.
Behaviour and Compatibility
This species is known to be very peaceful, but it may not be the best choice for a community tank due to its small size and timid nature. It is recommended to keep this fish with other peaceful characids and smaller catfish species such as callichthyids or loricariids. It can also be a great addition as a dither fish for Apistogramma spp. and other dwarf cichlids.
Because it is a gregarious animal, it is recommended to purchase as many as possible, ideally 10 or more, as they will exhibit more natural behavior and any aggression will be spread out among individuals. Additionally, keeping them in larger groups will make the fish bolder and less likely to be stressed.
Although this species is generally peaceful, it is important to note that individual fish may display territorial behavior towards others of the same species, particularly when breeding. If breeding is desired, it is best to keep a larger group in a well-planted aquarium with plenty of hiding places to disperse aggression.
It is worth noting that some individuals of this species may exhibit a larger and more rounded body shape, which is likely to be characteristic of adult females.
The Gasteropelecidae family is distinctive from other Characiformes by its unique characteristics, including a longitudinally corrugated frontal bone with a strong longitudinal ridge, a fused posttemporal and supracleithrum bone, small pelvic fins and associated bones, and a greatly expanded coracoids that fuse to a single fan-shaped and corrugated median bone. The family also has a lateral line that extends ventroposteriorly to approach the anal-fin insertion, 0-2 or 3 scales behind the head, and one or very few scales on the caudal-fin base. Larger species have an adipose fin, while smaller species lack it. Currently, there are three valid genera of Gasteropelecidae, with Carnegiella being the most diverse, consisting of four small species that lack an adipose fin.
The species in Carnegiella show geographic variations based on their locality, with the marble hatchetfish C. strigata being a prime example. At various times, it has had five recognized species. Gery (1977) noted that the species in this genus are polytipic, meaning that there are two or more distinct populations within each species. He suggested that the Orinoco and Negro system fish of the C. marthae group should be considered a subspecies, C. marthae marthae, and the species C. schereri from the Peruvian Amazon as the subspecies C. marthae schereri. Recent research by Piggott et al. (2011) identified three cryptic species in the Negro floodplain streams.
Due to their unique body shape, gasteropelecids are commonly known as freshwater hatchetfishes. Their bodies are heavily-keeled, which is due to an enlarged, heavily-muscled pectoral girdle, giving them a shape resembling the head of a hatchet.
It is sometimes said that hatchetfish can fly above the water surface by beating their pectoral fins, but this is not true. Wiest’s (1995) research using high-speed video photography disproved this myth. He found that the pectoral fins are used to leave the water but not while the fish is in the air. Instead, hatchetfish are capable of powerful jumps, which are actually a modified threat response used in extreme circumstances, much like other fishes.
Interestingly, Wiest also discovered that hatchetfish can only jump once or twice before needing a rest due to the amount of energy required to work their massive pectoral girdle muscles. When fatigued, they revert to a typical diving response.
Furthermore, anecdotal evidence from fish collectors and ichthyologists working in the field suggests that hatchetfish rarely jump and tend not to do so in aquariums, even when chased with a net. However, during darkness, they may jump, and leaving the aquarium cover slightly open can result in hatchetfish on the floor by morning.
The order Characiformes is known for its vast diversity of freshwater fish species, with almost 2000 valid species spread across 19 families. However, this taxonomic and morphological diversity has presented a challenge for researchers attempting to determine genetic relationships between genera, with many remaining incertae sedis. In many cases, exhaustive individual studies have been necessary to address these issues.
Nonetheless, modern molecular phylogenetic techniques have allowed researchers to make some progress in this area. For instance, Javonillo et al. (2010) and Oliveira et al. (2011) published research papers that offered some hypotheses about genetic relationships within the order. The former paper suggested that the family Gasteropelecidae forms a monophyletic clade nested within the family Characidae. Meanwhile, the latter paper expanded on this hypothesis and proposed that within the family, Carnegiella is the sister group of Gasteropelecus, with Thoracocharax sister to that clade.
Additionally, the authors suggested that Gasteropelecidae is most closely related to their expanded Bryconidae, which includes the genera Brycon, Henochilus, and Salminus. Other researchers, 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.
- Myers, G. S., 1927 – Bulletin of the Museum of Comparative Zoology 68(3): 107-135
Descriptions of new South American fresh-water fishes collected by Dr. Carl Ternetz.
- Gery, Jacques, 1977 – TFH Publications Inc.
Characoids of the World
- Javonillo, R., L. R. Malabarba, S. H. Weitzman and J. R. Burns, 2010 – Molecular Phylogenetics and Evolution 54(2): 498-511
Relationships among major lineages of characid fishes (Teleostei: Ostariophysi: Characiformes), based on molecular sequence data.
- Oliveira, O., G. S Avelino, K. T. Abe, T. C Mariguela, R.C Benine, G. Ortí, R. P. Vari and R. M. Corrêa e Castro, 2011 – BMC Evolutionary Biology 11: 275
Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling.
- Piggott, M. P., N. L. Chao and L. B. Beheregaray, 2011 – Biological Journal of the Linnean Society 102(2): 391-403
Three fishes in one: cryptic species in an Amazonian floodplain forest specialist.
- Reis, R. E., S. O. Kullander and C. J. Ferraris, Jr. (eds.), 2003 – EDIPUCRS, Porto Alegre: i-xi + 1-729
Check list of the freshwater fishes of South and Central America. CLOFFSCA.
- Weitzman, S. H. and L. Palmer, 1996 – Tropical Fish Hobbyist 45(1): 195-206
Do freshwater hatchetfishes really fly?
- Wiest, F. C., 1995 – Journal of Zoology 236(4): 571-592
The specialized locomotory apparatus of the freshwater hatchetfish family Gasteropelecidae