Carnegiella marthae
Blackwing Hatchetfish
Etymology
Carnegiella: erected in 1909 by C.H. Eigenmann for the type species C. strigata (which was at that time named Gasteropelecus strigatus); the name honours Miss Margaret Carnegie and was chosen to represent the gracefulness of these fish.
marthae: named for the author’s wife, Martha, who was especially fond of this fish.
Classification
Order: Characiformes Family: Gasteropelecidae
Distribution
Type locality is ‘ Caño de Quiribana, near Caicara, Venezuela’ and this species is currently considered to range throughout the upper Orinoco drainage in Venezuela and rio Negro drainage in Amazonian Brazil with the occasional specimen also having been recorded from the rio Madeira which enters the Amazon downstream from the mouth of the Negro on the opposite bank.
It may also occur in Colombia with at least one record existing from the Río Vichada and another from the Río Inírida, both tributaries of the Orinoco.
It may turn out to have a more-restricted distribution, though, with research published by Piggott et al. (2011) suggesting the existence of at least three species in the Rio Negro basin alone (see ‘Notes’).
Habitat
Appears to be a stenotypic inhabitant of blackwater environments.
In the rio Negro system it inhabits so-called igapó and igarapé habitats characterised by thick, often overhanging, riparian vegetation and substrates covered in fallen branches, tree roots and leaf litter.
The water is typically acidic, of negligible carbonate hardness and conductivity and stained brownish due to the presence of humic substances released by decomposing organic matter.
The Negro has a substantial floodplain and the water level can rise by up to 15 metres during the annual wet season.
During the period of inundation small fishes such as C. marthae move upstream within the river’s tributaries and then laterally into the flooded forest itself to feed and reproduce, before returning to the tributaries when the water falls.
Maximum Standard Length
The largest officially-recorded specimen measured 28.1 mm.
Aquarium SizeTop ↑
Surface dimensions of 60 ∗ 30 cm or more are recommended since this species should be maintained in numbers (see ‘Behaviour and Commpatibility’).
Maintenance
Should ideally be maintained in a heavily-planted set-up, preferably with a dark substrate and some patches of floating vegetation around which the fish will tend to congregate since they spend almost all of their time at or towards the surface.
Driftwood branches and dried leaf litter can also be added, the latter in particular driving establishment of microbe colonies as decomposition occurs.
Such microorganisms can provide a valuable secondary food source for fry, whilst the tannins and other chemicals released by the decaying leaves are also thought beneficial.
Water movement should be gentle to moderate and be sure that the aquarium cover is tightly-fitting as this species may jump when startled (but see ‘Notes’).
Water Conditions
Temperature: 20 – 28 °C
pH: 4.0 – 7.0
Hardness: 18 – 179 ppm
Diet
Primarily a predator feeding on terrestrial and aquatic invertebrates and other zooplankton taken at or near the water surface in nature.
In the aquarium it will accept dried foods of a suitable size but should also be offered regular meals of small live and frozen fare such as Artemia nauplii, Daphnia, Moina, grindal worm, etc.
Small insects such as young crickets or Drosophila fruit flies are also suitable to use although, it is best to fill the stomachs of these by feeding them fish flakes or some kind of vegetable matter before offering them to the fish.
Behaviour and CompatibilityTop ↑
Very peaceful but does not make an ideal community fish due to its small size and rather timid nature.
In a community it is best kept with similarly-sized, peaceful characids, and smaller callichthyid or loricariid catfishes.
It also makes an ideal 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.
It is very much a gregarious animal so buy as many as possible, ideally 10 or more, as when kept in larger groups any aggression is spread between individuals plus the fish are bolder and exhibit more natural behaviour.
Sexual Dimorphism
Some specimens do grow larger and become rounder-bodied than others, and presumably these represent adult females.
Reproduction
Unrecorded.
NotesTop ↑
The family Gasteropelecidae is separated from other Characiformes by the following combination of characters: frontal bone longitudinally corrugated with a strong longitudinal ridge; posttemporal and supracleithrum fused into a single bone; pelvic fins and associated bones minutehey; presence of an enlarged, strongly convex muscular pectoral girdle region, consisting of greatly expanded coracoids fused to a single fan-shaped and corrugated median bone; lateral line extending ventroposteriorly to approach the anal-fin insertion; 0-2 or 3 scales behind head and one or very few scales on caudal-fin base; 10-17 dorsal-fin rays; 22-44 anal-fin rays; adipose-fin present in larger species, absent in smaller species.
There are currently three valid genera of which Carnegiella is the most speciose with four members, all of which are smaller and lacking an adipose fin.
The species in Carnegiella show geographic variations according to the locality. This has long been recognized with the marble hatchetfish C. strigata which at various times had five recognized species. Gery (1977) noted that the species in this genus are polytipic, meaning that there are two or more distinct populations that can be recognized 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 the subspecies C. marthae schereri. The recent work by Piggott et al. (2011) identifies three cryptic species in the Negro floodplain streams.
Gasteropelecids are commonly-referred to as ‘freshwater hatchetfishes’ due to their heavily-keeled body shape which has evolved in such a way due to possessing an enlarged, heavily-muscled pectoral girdle, and which resembles the shape of a hatchet head.
They are sometimes said to be capable of propelled flight above the water surface by beating their pectoral fins but in fact this is not the case and was disproven by Wiest (1995) who used hugh speed video photography to demonstrate that the pectoral fins are used in leaving the water but not while the fish is in the air.
The action is more accurately described as a powerful jump and is actually a modified threat response which only appears to be used in extreme circumstances much like in many other fishes.
The researcher also found that the fish only seem to be able to jump once or twice before requiring a rest period due to the large amount of energy required to work the massive pectoral girdle muscles, and when fatigued their threat response is comparable to that of other small species in that they dive towards the substrate.
In addition anecdotal evidence from fish collectors and icthyologists working in the field would suggest that gasteropelecids rarely jump and they also tend not to do so in aquaria, even when being chased with a net (pers. obv.). However, during darkness the fish do jump, and leaving the cover open even slightly can result in one or more hatchetfish on the floor by morning.
Characiformes is among the most diverse orders of freshwater fishes currently including close to 2000 valid species distributed among 19 families.
This tremendous taxonomical and morphological diversity has historically impaired the ability of researchers to resolve their genetic relationships with many genera remaining incertae sedis.
A further limiting factor has been that in many cases exhaustive study of these on an individual basis is the only way to resolve such problems.
Modern molecular phylogenetic techniques have allowed some headway, though, and research papers by Javonillo et al. and Oliveira et al., published in 2010 and 2011, respectively, revealed some interesting hypotheses.
The results of the former suggest that Gasteropelecidae forms a monophyletic clade nested within the family Characidae, while the latter expanded on this and concluded that within the family Carnegiella is the sister group of Gasteropelecus with Thoracocharax sister to that clade, and that Gasteropelecidae appears most closely-related to the authors’ expanded Bryconidae which contains the genera Brycon, Henochilus and Salminus.
Others such as Oliveira et al. (2011) have concluded that the family Erythrinidae is also closely-related to this grouping with Hepsetidae and Alestidae more distant.
References
- 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.
