Taxonomy & naming
Carnegiella myersi was described by the Venezuelan ichthyologist Agustín Fernández-Yépez in 1950. The type locality is a creek near Yurimaguas, in the Loreto region of Peru, within the upper Amazon drainage. Eschmeyer's Catalog of Fishes recognises the valid name as Carnegiella myersi Fernández-Yépez, 1950, with the authority unparenthesised because the species has not been moved from the genus in which it was originally placed.
The genus Carnegiella belongs to the family Gasteropelecidae, the freshwater hatchetfishes — a small South American family of characteristically deep-chested, surface-dwelling characoids. Carnegiella is the smallest genus in the family, comprising a handful of species all under 1.5 in. C. myersi is the smallest of these and is readily distinguished by its size and relatively slender body; a Bolivian population has been noted as deeper-bodied than the Peruvian Amazon form, suggesting possible geographic variation within the species.
Morphology
Carnegiella myersi reaches a maximum of approximately 1 in standard length (roughly 1 in), making it one of the tiniest vertebrates commonly kept in the aquarium hobby. Like all hatchetfishes, it has a dramatically compressed, deep-bellied body: the ventral keel is large, rounded, and prominent, housing the greatly enlarged pectoral-girdle musculature that powers the family's rapid surface escape bursts. The mouth is steeply upturned, adapted to picking prey from the surface film.
The body is almost transparent, overlaid with a silvery-grey sheen. A crisp dark line runs along the flank, and the belly edge is sharply darkened. Fine black speckling is scattered across the flanks and fins. The overall impression is of a tiny sliver of water-surface life — inconspicuous from below but distinctive in hand. Sexual dimorphism is subtle; females are presumed to be more rounded in the belly when gravid, but the difference is not reliably used for sexing in normal aquarium conditions.
Habitat
In the wild, Carnegiella myersi occupies the Amazon basin of Bolivia and Peru, in slow-moving rivers, woodland streams, and marshes at low elevations. It is a pelagic, surface-dwelling species, spending most of its time at or just beneath the water's surface, in areas with overhanging or floating vegetation that provides shade and cover. It is typically found in small groups in still or near-still water with minimal current.
The preferred habitat reflects the soft, acidic blackwater conditions common to lowland Amazonian forest streams: FishBase records water parameters of 73–79 °F and pH 5.5–6.5. The shaded microhabitat reduces exposure to aerial predators, and the species' capacity for brief surface jumps — common to all hatchetfishes — is a last-resort escape response. Tanks must be kept covered for this reason.
Feeding
Carnegiella myersi is an insectivore by inclination, taking small invertebrates — insects and their larvae — at or near the water surface in the wild. Its upturned mouth and surface-orientated posture are structural adaptations to this feeding mode, and it rarely descends to the mid-water or bottom to feed.
In the aquarium, it accepts a range of appropriately small foods: flake broken small, micro pellets, small dried insects, and frozen or live invertebrates such as Daphnia, baby brine shrimp, or bloodworm. Foods must be small enough to fit the tiny mouth and ideally float or sink slowly enough to be intercepted at the surface. Feeding at the surface level, or using foods that float, is the practical approach; the fish tends to ignore food that has sunk past its comfort zone.
Mating
Carnegiella myersi is presumed to be an egg-scattering open-water spawner in line with the reproductive biology described for other hatchetfishes, though captive reproduction has not been formally documented for this species. As with related Carnegiella, any courtship behaviour likely takes place near the surface, consistent with the species' habitat preference.
Sexual dimorphism is minimal and pairing is difficult outside of the breeding season. Females are presumed rounder in the belly when reproductively active. The species is typically kept in groups, and any spawning that occurs in a community tank would go largely unobserved given the eggs' small size and the absence of parental behaviour.
Breeding
Captive breeding of Carnegiella myersi has not been recorded in the published literature, and virtually all fish in the trade are wild-caught. This contrasts with some larger hatchetfishes that have occasionally been bred in dedicated set-ups. The presumed mode, based on family characteristics, would be egg scattering among fine-leaved floating or near-surface plants, with adhesive or semi-adhesive eggs deposited without parental care.
Any attempt at breeding would require very soft, acidic, warm water closely matching the species' Amazonian origin, with minimal disturbance and a plentiful supply of small live foods to bring fish into condition. The practical obstacles — small size, difficult sexing, and undocumented husbandry — mean that captive-bred specimens remain essentially unavailable in the hobby.
In the aquarium
Carnegiella myersi is a delicate but rewarding fish for a species-appropriate set-up or a carefully selected community. Its tiny size (under 1 in) demands small, gentle tankmates: dwarf rasboras, small pencilfish, Corydoras pygmaeus or similar micro-catfishes, and small ornamental shrimp are compatible neighbours. Larger or more active fishes will outcompete it at feeding or stress it into hiding.
The tank should replicate the shaded, still-water blackwater environment: dim lighting or heavy floating plant cover, minimal water movement, soft and acidic water (pH 5.5–6.5, 73–79 °F), and a well-matured filter. A tight-fitting lid is essential — hatchetfishes jump readily and without warning. A group of at least six is recommended; smaller numbers produce nervous, stressed fish that hide constantly. This is not a beginner's fish: it requires stable water chemistry, appropriately sized food, and careful acclimation, but a well-settled group at the surface of a planted blackwater tank is a genuinely striking sight.
Conservation
Carnegiella myersi is assessed as Least Concern (LC) on the IUCN Red List, an assessment derived from its relatively wide range across the Bolivian and Peruvian Amazon and its status as locally common within suitable habitat. It is regularly collected for the international ornamental-fish trade, and commercial capture is noted as the primary human interaction with wild populations.
Although the species is not currently threatened, the long-term sustainability of wild collection depends on the preservation of lowland Amazonian forest habitats and the small-stream systems the fish occupies. Deforestation and agricultural expansion in the western Amazon continue to reduce and degrade these habitats. Because captive breeding is essentially undocumented, the aquarium trade for this species remains entirely dependent on wild harvest, which places a modest but ongoing pressure on wild populations.