Blackwing Hatchetfish (Carnegiella marthae)
A pocket-sized surface acrobat with jet-black 'wings' that leaps out of the water with genuine flight muscles — the most athletic nano fish in the hobby.
Will it live with a Blackwing Hatchetfish?
We compare each fish against your blackwing hatchetfish on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- African Dwarf Frog✅ CompatiblePeaceful · 4 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Amapá Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 24–27 °C (75–81 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Amapá Tetra in a shoal of 6+ or it gets stressed and nippy.
- Blue Danio✅ CompatiblePeaceful · 4 cm · Easy care · 21–26 °C (70–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Blue Emperor Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 23–27 °C (73–81 °F)
- Both are peaceful, and their water overlaps around 23–27 °C — no size, zone or temperament conflicts.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Blue Emperor Tetra in a shoal of 6+ or it gets stressed and nippy.
- Cardinal Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 23–27 °C (73–81 °F)
- Compatible on the things that matter: shared water near 23–27 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Cardinal Tetra in a shoal of 6+ or it gets stressed and nippy.
- Clown Killifish✅ CompatiblePeaceful · 3.5 cm · Medium care · 22–26 °C (72–79 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the top of the tank — offer enough cover so they aren't always in each other's space.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Clown Killifish in a shoal of 6+ or it gets stressed and nippy.
- Crimson Red Betta✅ CompatiblePeaceful · 3.5 cm · Hard care · 24–29 °C (75–84 °F)
- Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Emperor Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 23–27 °C (73–81 °F)
- Both are peaceful, and their water overlaps around 23–27 °C — no size, zone or temperament conflicts.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Emperor Tetra in a shoal of 6+ or it gets stressed and nippy.
- Eyespot Rasbora✅ CompatiblePeaceful · 3.5 cm · Medium care · 20–25 °C (68–77 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Eyespot Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Fire Red Licorice Gourami✅ CompatiblePeaceful · 3.5 cm · Hard care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Flame Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Flame Tetra in a shoal of 6+ or it gets stressed and nippy.
- Ghost Shrimp✅ CompatiblePeaceful · 4 cm · Easy care · 18–28 °C (64–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Ghost Shrimp in a shoal of 6+ or it gets stressed and nippy.
- Glowlight Rasbora✅ CompatiblePeaceful · 3.5 cm · Easy care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Glowlight Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Glowlight Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Glowlight Tetra in a shoal of 6+ or it gets stressed and nippy.
- Golden Dwarf Barb✅ CompatiblePeaceful · 4 cm · Easy care · 18–24 °C (64–75 °F)
- Compatible on the things that matter: shared water near 23–24 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Golden Dwarf Barb in a shoal of 6+ or it gets stressed and nippy.
- Jelly Bean Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 20–26 °C (68–79 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Jelly Bean Tetra in a shoal of 10+ or it gets stressed and nippy.
- Marbled Hatchetfish✅ CompatiblePeaceful · 4 cm · Medium care · 23–28 °C (73–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the top of the tank — offer enough cover so they aren't always in each other's space.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Marbled Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Northern Glowlight Danio✅ CompatiblePeaceful · 3.5 cm · Medium care · 18–24 °C (64–75 °F)
- Compatible on the things that matter: shared water near 23–24 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Northern Glowlight Danio in a shoal of 8+ or it gets stressed and nippy.
- Otocinclus✅ CompatiblePeaceful · 4 cm · Medium care · 21–26 °C (70–79 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Otocinclus in a shoal of 6+ or it gets stressed and nippy.
- Phoenix Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 23–28 °C (73–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Phoenix Tetra in a shoal of 8+ or it gets stressed and nippy.
- Purple Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Purple Tetra in a shoal of 8+ or it gets stressed and nippy.
- Pygmy Corydoras✅ CompatiblePeaceful · 3.2 cm · Easy care · 22–26 °C (72–79 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Pygmy Corydoras in a shoal of 8+ or it gets stressed and nippy.
- Red Phantom Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Red Phantom Tetra in a shoal of 8+ or it gets stressed and nippy.
- Tailspotted Oto✅ CompatiblePeaceful · 3.5 cm · Medium care · 22–27 °C (72–81 °F)
- Both are peaceful, and their water overlaps around 23–27 °C — no size, zone or temperament conflicts.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Tailspotted Oto in a shoal of 6+ or it gets stressed and nippy.
- Black Darter Tetra⚠️ With cautionSemi-aggressive · 4 cm · Hard care · 21–28 °C (70–82 °F)
- Expect Black Darter Tetra to harass Blackwing Hatchetfish at times; give dense cover and watch them at feeding.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Black Ruby Barb⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Expect Black Ruby Barb to harass Blackwing Hatchetfish at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~100 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Black Ruby Barb in a shoal of 6+ or it gets stressed and nippy.
- Black Skirt Tetra⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 20–26 °C (68–79 °F)
- Expect Black Skirt Tetra to harass Blackwing Hatchetfish at times; give dense cover and watch them at feeding.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Black Skirt Tetra in a shoal of 6+ or it gets stressed and nippy.
- Blue Turbo Snail⚠️ With cautionPeaceful · 5 cm · Medium care · 25–30 °C (77–86 °F)
- pH preferences only just meet (Blackwing Hatchetfish 5.5–7 vs Blue Turbo Snail 7.5–8.5) — target the overlap and acclimate slowly.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Desert Goby⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 18–28 °C (64–82 °F)
- Expect Desert Goby to harass Blackwing Hatchetfish at times; give dense cover and watch them at feeding.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Dwarf Chain Loach⚠️ With cautionPeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Dwarf Chain Loach in a shoal of 6+ or it gets stressed and nippy.
- Eastern Betta⚠️ With cautionSemi-aggressive · 6 cm · Medium care · 24–28 °C (75–82 °F)
- Eastern Betta is semi-aggressive and may chase or nip the smaller Blackwing Hatchetfish — plant heavily and break up sight lines.
- Eastern Betta may hunt Blackwing Hatchetfish, fry or shrimplets — safest in a heavily planted tank.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Humpbacked Tetra⚠️ With cautionSemi-aggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Humpbacked Tetra is semi-aggressive and may chase or nip the smaller Blackwing Hatchetfish — plant heavily and break up sight lines.
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Humpbacked Tetra in a shoal of 8+ or it gets stressed and nippy.
- Morse Code Corydoras⚠️ With cautionPeaceful · 5 cm · Medium care · 23–26 °C (73–79 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Morse Code Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Rainbow Emperor Tetra⚠️ With cautionSemi-aggressive · 3.6 cm · Medium care · 22–28 °C (72–82 °F)
- Rainbow Emperor Tetra and Blackwing Hatchetfish are close in size, but the semi-aggressive one tends to dominate — add blackwing hatchetfish in a group to spread the pressure.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
- Serpae Tetra⚠️ With cautionSemi-aggressive · 4 cm · Easy care · 23–28 °C (73–82 °F)
- Serpae Tetra and Blackwing Hatchetfish are close in size, but the semi-aggressive one tends to dominate — add blackwing hatchetfish in a group to spread the pressure.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Serpae Tetra in a shoal of 6+ or it gets stressed and nippy.
- Silvertip Tetra⚠️ With cautionSemi-aggressive · 5 cm · Easy care · 22–28 °C (72–82 °F)
- Silvertip Tetra is semi-aggressive and may chase or nip the smaller Blackwing Hatchetfish — plant heavily and break up sight lines.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Keep Silvertip Tetra in a shoal of 6+ or it gets stressed and nippy.
- Spotfin Betta⚠️ With cautionSemi-aggressive · 5 cm · Medium care · 23–28 °C (73–82 °F)
- Spotfin Betta and Blackwing Hatchetfish are close in size, but the semi-aggressive one tends to dominate — add blackwing hatchetfish in a group to spread the pressure.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Striped Red-Eye Puffer⚠️ With cautionAggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Striped Red-Eye Puffer and Blackwing Hatchetfish are close in size, but the aggressive one tends to dominate — add blackwing hatchetfish in a group to spread the pressure.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Tiger Badis⚠️ With cautionSemi-aggressive · 4 cm · Medium care · 22–24 °C (72–75 °F)
- Tiger Badis is semi-aggressive and may chase or nip the smaller Blackwing Hatchetfish — plant heavily and break up sight lines.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Wine Red Betta⚠️ With cautionAggressive · 5 cm · Medium care · 24–28 °C (75–82 °F)
- Expect Wine Red Betta to harass Blackwing Hatchetfish at times; give dense cover and watch them at feeding.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Alligator Gar⛔ Not recommendedAggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Alligator Gar (250 cm) is big enough to swallow the 3.5 cm Blackwing Hatchetfish whole.
- Alligator Gar is aggressive and may chase or nip the smaller Blackwing Hatchetfish — plant heavily and break up sight lines.
- Your 75 L tank is below the ~3785 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Clown Knifefish⛔ Not recommendedAggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
- Size gap is too large (90 vs 3.5 cm): Clown Knifefish will treat Blackwing Hatchetfish as food.
- Clown Knifefish clearly outsizes Blackwing Hatchetfish and is aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Fire Eel⛔ Not recommendedSemi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Size gap is too large (100 vs 3.5 cm): Fire Eel will treat Blackwing Hatchetfish as food.
- Fire Eel is semi-aggressive and may chase or nip the smaller Blackwing Hatchetfish — plant heavily and break up sight lines.
- Your 75 L tank is below the ~380 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Koi⛔ Not recommendedPeaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
- Size gap is too large (90 vs 3.5 cm): Koi will treat Blackwing Hatchetfish as food.
- Your 75 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Redtail Catfish⛔ Not recommendedAggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Blackwing Hatchetfish is bite-sized to a 120 cm predatory redtail catfish — it will be eaten.
- Redtail Catfish clearly outsizes Blackwing Hatchetfish and is aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Spotted Gar⛔ Not recommendedAggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Size gap is too large (90 vs 3.5 cm): Spotted Gar will treat Blackwing Hatchetfish as food.
- Spotted Gar clearly outsizes Blackwing Hatchetfish and is aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Wels Catfish⛔ Not recommendedAggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Blackwing Hatchetfish is bite-sized to a 300 cm predatory wels catfish — it will be eaten.
- Wels Catfish is aggressive and may chase or nip the smaller Blackwing Hatchetfish — plant heavily and break up sight lines.
- Your 75 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Wolf Cichlid⛔ Not recommendedAggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Blackwing Hatchetfish is bite-sized to a 72 cm predatory wolf cichlid — it will be eaten.
- Expect Wolf Cichlid to harass Blackwing Hatchetfish at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.
Blackwing Hatchetfish care specs
- Care level
- Medium
- Breeding
- Very Hard
- Max size
- 3.5 cm (1.4 in)
- Min tank size
- 60 L (15.9 gal)
- Temperature
- 23–28 °C (73–82 °F)
- pH
- 5.5–7
- Hardness
- 1–10 dGH
- Lifespan
- 3–5 years
- Diet
- Carnivore
- Swim level
- Top
- Group size
- 6+ (shoaling)
- Family
- Gasteropelecidae
- Origin
- South America — Orinoco and upper Rio Negro basins, Venezuela and Colombia
What is a Blackwing Hatchetfish?
The blackwing hatchetfish (Carnegiella marthae) is one of the smallest and most distinctive surface-dwellers available to freshwater aquarists. Reaching just 3.5 cm (about 1.4 in) at maturity, it is dwarfed by many nano fish, yet its body plan is immediately striking: a dramatically deep, keel-shaped chest houses genuine flight muscles — not just fins adapted for gliding, but real musculature capable of powering brief aerial bursts above the waterline when the fish is startled or chasing prey. The silver flanks are bisected by a sharp, jet-black lateral band, and the enlarged pectoral fins carry dark pigment that earns the species its common name.
In the wild, blackwing hatchetfish hug the surface film of slow, shaded blackwater streams and flooded forest pools, picking off insects that fall from the canopy. In aquaria, they replicate this behaviour precisely — spending virtually their entire lives in the top few centimetres of the water column, rarely venturing deeper. They are peaceful, shoaling fish that do best in a tight group of six or more, where they form a shimmering, coordinated layer at the surface. For aquarists willing to meet their specific water-chemistry demands, they are one of the most rewarding and visually unusual nano species in the hobby.
Where do Blackwing Hatchetfish come from?
Carnegiella marthae is native to the Orinoco basin and the upper Rio Negro drainage in Venezuela and Colombia — two of South America’s great blackwater river systems. “Blackwater” refers to water stained dark amber or brown by dissolved tannins and humic acids leaching from leaf litter and submerged wood. This water is characteristically very soft (1–10 dGH), acidic (pH often 4.5–6.5 in the wild), low in dissolved minerals, and frequently stained to the point of near-opacity in the shaded stream margins these fish prefer.
The habitat is typically slow-moving or still, heavily shaded by dense riparian vegetation, and the surface is often partly covered by floating leaves and debris. Temperatures in these equatorial streams range from about 23–28 °C (73–82 °F) year-round. These conditions are quite specific and directly inform why the species has a reputation for being sensitive in captivity — not because it is fragile by nature, but because it is a fish built for very particular chemistry that most tap water does not naturally provide.
What tank size and setup do Blackwing Hatchetfish need?
A minimum of 60 litres (16 gallons) is needed for a group of six, and a longer, shallower tank footprint is far preferable to a tall one. Blackwing hatchetfish live almost exclusively at the surface, so horizontal swimming length matters far more than depth. A tank measuring 75–90 cm (30–36 in) in length gives the shoal room to move and reduces the inter-fish tension that can develop in cramped quarters.
Filtration should provide gentle turnover — a sponge filter or a hang-on-back filter with a spray-bar return set near the surface is ideal. Strong turbulence at the surface stresses surface-dwelling fish and can interfere with feeding. Lighting should be moderate to low; in the wild these fish live under dense canopy shade.
Floating cover is essential. Amazon frogbit, water lettuce, or patches of floating hornwort replicate the overhead shelter these fish seek and significantly reduce the urge to jump. Beyond the floating layer, the rest of the tank can be aquascaped to taste — dense stem plants, driftwood, and botanical leaf litter all reinforce the blackwater aesthetic and help buffer water chemistry. A dark substrate of sand or fine gravel further reduces stress.
The most critical hardware decision is the lid. Hatchetfish are powerful, accurate jumpers that will clear any gap. A fully sealed, tight-fitting lid — with foam or tape blocking any gap around filter tubes or heater cords — is non-negotiable.
What water parameters do Blackwing Hatchetfish need?
- Temperature: 23–28 °C (73–82 °F)
- pH: 5.5–7.0
- Hardness: 1–10 dGH (soft to very soft)
These are soft-acidic blackwater parameters, and the hardness target in particular is lower than most community fish accept. Ordinary tap water in many cities runs at 10–25 dGH and pH 7.0–8.5 — fine for livebearers and cichlids, but chronically stressful for this species. The practical solution is to blend reverse-osmosis (RO) water with a small proportion of dechlorinated tap water and remineralise lightly, targeting the lower half of the pH and hardness ranges. Alternatively, a peat-filtered or botanical-softened setup using dried botanicals (Indian almond leaves, alder cones) in the filter or on the substrate will gradually acidify and soften the water while releasing the tannins that colour a natural blackwater display.
Test water chemistry before purchase and establish stable parameters before introducing fish. Weekly water changes of 20–25% with prepared soft-acidic water maintain quality without large parameter swings.
What do Blackwing Hatchetfish eat?
Blackwing hatchetfish are carnivores built to feed at the surface film. In the wild, the bulk of their diet consists of small terrestrial insects, their larvae, and other invertebrates that fall onto the water. In captivity, they rarely pursue food that sinks more than a centimetre or two below the surface, so feeding strategy matters as much as food choice.
The best staples are:
- Wingless (flightless) fruit flies — near-ideal prey that triggers natural hunting behaviour and stays on the surface.
- Frozen or live daphnia — small enough for their mouths and accepted readily at the surface layer.
- Micro-worms and baby brine shrimp — useful variety, though these sink faster and should be fed in small portions.
- High-quality nano floating pellets or crushed flake — a practical everyday staple, accepted once the fish settle in.
Feed small amounts once or twice daily, only what the group consumes within two to three minutes. Uneaten food that sinks and decomposes is doubly problematic in the soft, low-buffering-capacity water these fish require.
What is the behaviour of Blackwing Hatchetfish, and what fish can they live with?
Blackwing hatchetfish are entirely peaceful and present no aggression toward tank-mates. Their only “behaviour problem” is their jumping ability — a consequence of their remarkable flight muscles — which is managed by the lid, not by companion selection. Within the shoal, they are social and calming to observe; a group of six or more moves as a loose, coordinated unit along the surface.
Because they occupy exclusively the top of the water column, they pair naturally with mid- and bottom-level species that do not compete for surface space or food. Ideal companions in a soft-water community include pencilfish (Nannostomus spp.), small tetras adapted to soft water (such as cardinal tetras, rummy-nose tetras, or ember tetras), dwarf cichlids like apistogrammas, and small corydoras. Avoid boisterous or fin-nipping species, anything large enough to view them as prey, and any species that requires hard or alkaline water — the water-chemistry compromise will harm one group or the other.
For a full list of tested compatible and incompatible species, see Blackwing Hatchetfish tank mates.
How do you tell male from female Blackwing Hatchetfish apart?
Sexual dimorphism in Carnegiella marthae is subtle. Females tend to appear slightly rounder and fuller in the abdomen when viewed from directly above, particularly when they are carrying eggs. Males are comparatively slimmer in profile. The difference is most visible in a mature, well-conditioned group rather than in an individual fish, and it can be very difficult to detect in juveniles or in fish that are not in optimal condition. For most hobbyists, sexing hatchetfish is primarily relevant when attempting to breed them — for display purposes, a group of six to eight fish of mixed sex will work perfectly well together.
How do Blackwing Hatchetfish breed?
Breeding Carnegiella marthae in captivity is rated very hard and has been achieved by only a small number of dedicated specialists. The challenges are multiple: the fish require near-perfect blackwater conditions (very low pH, very low hardness, dim lighting, and pristine water quality) to even consider spawning; eggs are scattered near or at the surface among floating plants; the eggs and fry are extremely small and sensitive; and the adults will readily consume eggs if not separated immediately after spawning.
A breeding attempt typically requires a dedicated, bare-bottomed or fine-substrate breeding tank set up with heavily conditioned blackwater, a dense mat of floating plants to provide a spawning site, and careful conditioning of pairs or groups on live foods over several weeks. If spawning occurs, adults should be removed promptly. First foods for fry are infusoria and commercial fry foods of the finest grade, graduating to baby brine shrimp as the fry grow. This is a project for experienced soft-water specialists, not a beginner’s first breeding attempt.
What diseases are common in Blackwing Hatchetfish?
Blackwing hatchetfish are not especially disease-prone when kept in appropriate conditions, but they are more sensitive than hardy community species and will show stress-related illness quickly when water chemistry drifts.
- Ich (white spot): The classic opportunistic protozoan; appears as white spots on fins and body, most often triggered by temperature fluctuations or a compromised immune system from poor water quality. Prevention is stable temperature and good husbandry.
- Velvet: A golden, dusty film on the body caused by Oodinium — particularly dangerous in shoaling surface fish because it spreads rapidly through the group. Dim lighting during an outbreak helps slow the parasite. Quarantine any new fish before introduction.
- Bacterial fin rot and bacterial infections: Usually secondary to water-quality lapses. Maintaining low nitrates and regular water changes is the primary prevention.
- Wasting / emaciation: Often seen in newly imported fish stressed by hard water or transport. Refusing surface food in a settled tank is a warning sign; check water chemistry first.
Health note: disease diagnosis and medication dosing are beyond the scope of a care profile. For a fish showing symptoms, cross-reference with a reputable veterinary or fish-health reference and confirm the diagnosis before treating. Treating the water quality issue first resolves the majority of common ailments.
How long do Blackwing Hatchetfish live?
In a well-maintained, species-appropriate setup, blackwing hatchetfish typically live 3–5 years. Achieving the upper end of that range depends heavily on water-chemistry stability — fish kept in chronically too-hard or too-alkaline water rarely reach their potential lifespan regardless of other care. Wild-caught individuals (which represent most of the trade supply, as captive breeding is uncommon) may arrive stressed from collection and transport, so a careful, patient acclimatisation period to the aquarium’s conditions is time well invested. A group of six kept in a soft-water blackwater display tank, fed varied live and frozen foods, and maintained with consistent partial water changes can be a long-lived, rewarding centrepiece in the surface layer for several years.
Frequently asked questions
Will blackwing hatchetfish jump out of the tank?
Yes — hatchetfish are famous jumpers and will launch themselves through any gap. A tight-fitting lid with no openings is non-negotiable; even a small gap near filter or heater tubes is enough for them to escape.
What water conditions do blackwing hatchetfish need?
They come from soft, acidic blackwater streams in the Orinoco and Rio Negro basins, so they do best in soft, slightly acidic water (pH 5.5–7.0, hardness 1–10 dGH). Hard or alkaline tap water stresses them; using reverse-osmosis water mixed with tap water or adding a botanicals/peat to soften it will greatly improve their long-term health.
What you need to keep a blackwing hatchetfish
The baseline is a heated, filtered 60 L+ tank: a reliable heater to hold 23–28 °C (73–82 °F), a gentle filter that won't batter a blackwing hatchetfish in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
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