Carnegiella marthae (Blackwing Hatchetfish)

30 May 2026

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The Blackwing Hatchetfish is a fascinating, peaceful surface-dweller native to the slow-moving, acidic waters of South America. Known for its uniquely deep, keeled belly and remarkable ability to leap from the water to catch insects, this distinctive schooling fish adds captivating upper-level activity to any well-covered community aquarium.

Carnegiella marthae (Blackwing Hatchetfish)

Overview

The Blackwing Hatchetfish (Carnegiella marthae) is an incredibly unique freshwater fish beloved for its distinctive profile and top-water antics. Belonging to the family Gasteropelecidae, these fish are true surface dwellers that rarely venture into the middle or lower levels of the aquarium. They are famous for their ability to jump or "fly" out of the water to evade predators or catch low-flying insects, making a tight-fitting aquarium lid an absolute necessity.

Image of blackwing hatchetfish carnegiella marthae

Distribution and Habitat

Native to South America, the Blackwing Hatchetfish is primarily found in the Orinoco and Rio Negro river basins in Venezuela and Brazil. They inhabit slow-moving, blackwater streams, tributaries, and flooded forest areas. These waters are typically heavily shaded by overhanging vegetation, stained dark with tannins from decaying leaves, and very soft and acidic.

Description of Blackwing Hatchetfish

Body shape:

They possess a highly specialized, laterally compressed body with a deeply keeled, convex belly that houses powerful muscles used for jumping.

Color:

The body is predominantly silver with a dark horizontal stripe running from the gills to the tail. Their most defining feature is the black edging and mottling along their prominent pectoral fins and lower keel.

Barbels:

This species does not possess barbels.

Snout:

They have a sharply upturned mouth perfectly adapted for feeding on insects and organic matter at the water's surface.

Eyes:

Their eyes are relatively large and positioned high on the head, allowing them to spot prey above the water line as well as predators below.

Fins:

The pectoral fins are greatly enlarged and wing-like, set high on the body to aid in their leaping ability. The dorsal and anal fins are relatively small and set far back on the body.

The Tail:

The caudal (tail) fin is forked and mostly clear, providing swift propulsion when the fish needs to quickly accelerate across the surface.

Temper

The Blackwing Hatchetfish is a very peaceful but skittish species. They are easily startled by sudden movements, loud noises, or aggressive tank mates, which can trigger their instinct to jump.

Sociality

This is a highly gregarious schooling fish. They feel most secure and display their best natural behaviors when kept in groups of at least six to eight individuals. Keeping them in smaller numbers will result in stress and a weakened immune system.

Activity

They are active swimmers that spend almost 100% of their time at the very top of the water column. They will often hover in the current, waiting for food to drift by, and will occasionally dart across the surface.

Keeping and Caring for Blackwing Hatchetfish

Tank size:

A minimum tank size of 15 to 20 gallons is required. Because they are surface dwellers, the footprint (length and width) of the tank is far more important than its depth. A completely secure, gap-free lid is mandatory to prevent them from jumping out.

Water Parameters:

Temperature

They thrive in warm tropical waters ranging from 23-27°C (73-81°F).

pH

They prefer slightly acidic conditions, with a pH range of 5.5 to 7.0 being ideal.

Hardness

Soft water is essential, ideally kept between 1 and 10 dGH.

Ammonia, Nitrite, Nitrate

Ammonia and Nitrite must always be at 0 ppm. Nitrates should be kept as low as possible, ideally below 20 ppm, through regular water changes.

Lighting

They prefer dim to moderate lighting. Bright lighting can cause stress unless it is heavily diffused by floating vegetation.

Water flow

A gentle to moderate surface flow mimics their natural stream habitat and encourages their natural hovering behavior.

Decorations and Plants

Floating plants (like Amazon Frogbit or Dwarf Water Lettuce) are highly recommended as they provide cover and make the fish feel secure. Driftwood and botanicals (like Indian almond leaves) can be added to the bottom to release beneficial tannins.

Diet

In the wild, they are primarily insectivores. In the aquarium, they will readily accept high-quality floating flakes or micro-pellets. To ensure optimal health, supplement their diet with freeze-dried, frozen, or live foods such as bloodworms, mosquito larvae, daphnia, and flightless fruit flies.

Some Feeding Tips

Because of their upturned mouths and surface-dwelling nature, they will rarely chase food as it sinks. Ensure you offer foods that stay afloat for a long time, and feed small amounts to prevent excess waste from sinking uneaten.

Breeding

Breeding the Blackwing Hatchetfish in captivity is considered difficult. They are egg scatterers that typically spawn among the roots of floating plants. To encourage spawning, the water must be very soft and acidic, and the breeding pair must be heavily conditioned with live insects. After spawning, the parents will eat the eggs, so they must be removed immediately. The fry are exceptionally tiny and require infusoria until they are large enough to accept baby brine shrimp.

Conclusion

The Blackwing Hatchetfish is a captivating addition to a peaceful, soft-water community tank. While they require a bit of extra care regarding water quality and an absolutely secure lid, their unique appearance and engaging surface behaviors make them a rewarding species for intermediate aquarists.

Fish info

Care level: Moderate
Temperament: Peaceful
Adult size: 3.5 cm
Life expectancy: 3-5 years
Fish type: Hatchetfish
Temperature : 23-27°C
pH: 5.5-7.0
Color Form: Black, Clear, Silver

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