Marbled Hatchetfish Care Guide

The marbled hatchetfish is an obligate surface fish and the best jumper of all the hatchetfishes, which makes one fact load-bearing above every other: a gap-free lid is the difference between a thriving shoal and a dried-out fish on the floor. It is a peaceful, soft-water blackwater shoaler — beautiful and rewarding, but wild-caught and finicky enough that it is not a true beginner fish.

Marbled Hatchetfish at a glance

The sourced figures the welfare engine uses to judge Marbled Hatchetfish — the parseable key facts.

Where it comes from

Carnegiella strigata is a characiform from northern South America — the Amazon and Orinoco basins and the Guianan coastal drainages — with most aquarium stock collected from the rio Negro in Brazil. Seriously Fish calls it an exclusive inhabitant of blackwater: igapó flooded forest and igarapé forest creeks under thick overhanging vegetation, in slow, dim, tea-coloured water that is acidic, very soft and stained brown with tannins. It lives its whole life in the top few centimetres, in groups near the surface, eating insects that drop from the overhanging plants. Every requirement follows from that: soft, acidic, tannin-stained, dimly-lit water to match the biotope; floating plants for overhead cover that turn a timid fish confident; gentle flow and a calm surface; and feeding at the top, because that is the only place it forages. One honest taxonomy note — despite our "Tetras" grouping, this is not a tetra. It shares the order Characiformes with tetras but belongs to the distinct family Gasteropelecidae, the freshwater hatchetfishes, so it should be called a hatchetfish on the page; genetic work even suggests the rio Negro "marbled hatchetfish" may be several lumped species.

Did you know?

• It is the "flying fish" of the aquarium, told honestly: reportedly the best jumper of all the hatchetfishes, it makes a powered leap and glides on rigidly-held pectoral "wings" — but whether it truly flaps in mid-air to power continued flight is genuinely disputed, so it's a great myth-bust rather than a fish that "flies."
• It is built around its chest muscles. An enormously enlarged sternal region — the "hatchet" keel — and oversized pectoral fins mean the associated muscles make up roughly a quarter of the fish's body weight.
• It is an obligate blackwater surface-dweller, spending its whole life in the top few centimetres of dim, tea-coloured forest water, eating insects that fall from overhanging plants.
• It is not a tetra. It shares the order Characiformes with tetras but belongs to the separate family Gasteropelecidae — and genetic work suggests the rio Negro "marbled hatchetfish" may be several species lumped under one name.
• Unlike most community fish, almost every marbled hatchet sold is collected from the wild rivers of the Amazon and rio Negro, not bred on a farm.

Tank size — and why

A 20-gallon tank (~75 L) is the practical floor for a proper group, but the real driver is surface area, not volume or bioload. This is a tiny, low-waste fish that swims horizontally near the top in a shoal, so what it needs is open surface footprint and length to school — Seriously Fish frames it as a 75 × 30 cm base, FishBase as about 80 cm of length for groups of five or more. A tall, narrow tank is poor for it; a long, broad-topped tank is ideal. Don't let raw gallons mislead you — a 20-gallon "long" beats a taller 20-gallon every time.

As a guide, a 20-gallon tank comfortably suits about 8–11 Marbled Hatchetfish as a single-species display, leaving room for tankmates.

See it to scale

Adult Marbled Hatchetfish reach only about 4 cm (1.6 in) long — close to the size they are sold at, so what you see is roughly what you get. The catch is the group: a proper shoal still needs about a 20-gallon tank, around 76 cm long.

Adult size is sourced; tank length is approximate for a standard 20-gallon aquarium.

Water parameters in practice

Match the blackwater origin. Temperature sits at 24–28 °C, with the comfortable middle around 24–27 °C (Seriously Fish tolerates down to 20 °C). On paper it survives a wide pH — FishBase lists up to 8.0 — but as a wild-caught soft-water specialist it thrives in the acidic, soft, tannic band it came from: aim for pH 5.5–6.5 and low hardness (roughly 1–12 °dGH). Hard, alkaline water is a chronic stressor that fades its colour and shortens its life. The pH floor in the literature runs surprisingly low (Seriously Fish notes 4.0, reflecting the wild extreme rather than a target), so 5.5–6.5 is the band to actually keep. For newly imported fish, stability and tannins matter more than chasing an exact number; a botanical, leaf-litter, driftwood-stained set-up suits them and brings out their behaviour.

Diet & feeding

It is a micropredator and insectivore that feeds at or near the surface — in the wild, terrestrial insects that fall onto the water from overhanging plants. The load-bearing point is that it is an obligate surface feeder: it lives mere centimetres below the top, takes food from the surface, and largely ignores anything that has sunk past it. It will not scavenge the bottom. Feed floating or slow-sinking flake and small micropellet as the staple, and offer live or frozen surface foods it relishes — brine shrimp nauplii, Daphnia, Moina, grindal worm, and especially small floating insects like wingless fruit flies and mosquito larvae that stay on top and trigger natural feeding. Newly arrived wild-caught fish are often finicky and may refuse dried food at first, needing live or frozen surface foods to start before being weaned onto flake. Feed small amounts once or twice a day; in a tank of greedy mid-water feeders it can slowly starve while looking fine.

Gear & setup

Build the setup around the lid. A gap-free, tightly-fitting cover over the entire surface is a hard requirement — treat it the way a pleco needs driftwood. It is the best jumper of the hatchetfishes and FishBase bluntly notes it may jump out of the aquarium, so glass-top the whole footprint and block every cut-out: filter outflow, heater and cable notches, feeding flaps, and the slot at the back of a hood are all escape routes. Leave a few centimetres of air below the lid, but no open holes. Add floating plants — Salvinia, frogbit, water sprite — as overhead cover that calms a timid fish and steadies the surface, keep the light dim, and run gentle flow without strong surface agitation, since they feed and rest at the top. Substrate and hardscape are for the tankmates and the blackwater look; the hatchet doesn't care what's on the bottom.

Temperament & behaviour

Very peaceful but distinctly timid and shy — no threat to tankmates and easily intimidated itself. It is an obligate shoaler, so group size is a welfare matter, not a preference: kept in twos and threes or with boisterous fish it hides, stops feeding and fades; in a real shoal it grows confident and cruises the open surface. Within the group it is essentially peaceful, with at most minor jostling that some sources loosely call "territorial with their own species" — a bigger group diffuses it. It spends its life in the top few centimetres, calm and slow when settled, but capable of explosive, startling jumps when alarmed.

Group & social needs

An obligate shoaling fish — keep six as a floor and, as Seriously Fish advises, ideally ten or more. This is a timid species that does markedly better in a larger group; small numbers are a genuine welfare failure rather than a budget compromise.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Marbled Hatchetfish and that suit its size and temperament best. Tap any to load the pairing in the planner.

• Amano Shrimp — Peaceful temperament, similar adult size.
• Assassin Snail — Uses the bottom zone, peaceful temperament, similar adult size.
• Black Neon Tetra — Uses the midwater zone, peaceful temperament, similar adult size.

A note on the shrimp and snails here: Marbled Hatchetfish is peaceful and generally invertebrate-safe — but almost any fish will take very small shrimplets given the chance, so give shrimp dense cover (moss, leaf litter) if you want a colony to grow, rather than expecting every baby to survive.

This engine-cleared shortlist is Marbled Hatchetfish's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Hard and rarely achieved — Seriously Fish records breeding as essentially unrecorded in the strict sense, though FishBase notes eggs hatch after about 36 hours at 25 °C and occasional hobby success exists. Because the species is wild-caught with no commercial breeding pipeline, reliable spawning information is thin. Sexing is difficult: the usual cue is that mature females grow slightly larger and rounder or deeper-bodied, especially when carrying eggs. When it does spawn, it wants very soft, acidic water and scatters sticky eggs among fine-leaved or floating plants and roots; adults eat the eggs, so remove them after spawning, and there is minimal parental care. Treat captive breeding as an advanced rarity, not a reason to buy the fish.

Lifespan

Relatively short-lived, and sources genuinely disagree — commonly about 2–3 years in captivity, occasionally up to ~5, with some hobby sources putting the marbled hatchet under 2 years. The short end is plausibly dragged down by the fact that nearly every fish is wild-caught and arrives already stressed and sometimes parasitised. What shortens it most is jumping out — the leading killer — followed by chronically wrong water (hard and alkaline for a soft-acid fish), failure to feed at the surface and slow starvation, untreated internal parasites from wild collection, and the stress of too small a group or rough acclimation.

Common mistakes

• No lid, or a lid with gaps. The classic and fatal mistake — it is the best jumper of the hatchetfishes, and leaping out to dry on the floor is the leading cause of death. Cover the entire surface gap-free, including filter, heater and cable cut-outs.
• Expecting it to eat off the bottom or from a normal community scrum. It is an obligate surface feeder; if other fish swarm the top first, it starves. Feed floating and surface foods deliberately.
• Buying 1–4 "to try them." A timid obligate shoaler — under-grouping makes it hide and fade. Keep six minimum, ideally ten or more.
• Hard, alkaline, brightly-lit water. The wrong biotope for a soft-acid blackwater fish; expect chronic stress and faded colour.
• Skipping quarantine on wild-caught stock. New imports are commonly parasitised and finicky first feeders.
• Boisterous or fast surface tankmates like bettas, tiger barbs or active danios, which out-compete and stress it.
• Strong surface agitation or a churning spray bar, which disrupts the calm surface it lives and feeds on.

Signs of trouble

• A sunken belly and disinterest in food — usually slow starvation from missed surface feeds, easy to overlook because the fish otherwise looks fine.
• Hiding in surface corners, isolating from the shoal, and clamped fins — timid stress, often too small a group or too-bold tankmates.
• Faded marbling and poor colour — typically the wrong water (too hard or alkaline) or chronic stress.
• Refusing food after import, with stringy or white faeces — a common sign of internal parasites in wild-caught fish.
• Gasping or surface-skimming distress; and watch for fish that have jumped into the lid or out of any gap.

Is this fish right for you?

Don't buy the marbled hatchetfish if you can't cover the entire surface gap-free — including every filter, heater and cable cut-out — because jumping out is the leading killer and a "tight" lid with holes isn't enough. Skip it if you can't feed floating and surface foods deliberately, if you only want a group of one to four, or if your tank is hard, alkaline and brightly lit. It is wild-caught with no farm-breeding pipeline, so new imports are often stressed, finicky first feeders and possible parasite carriers — buy healthy, already-eating, settled stock and quarantine it. There are no dyed or balloon morphs; the ethical issue is wild collection. Despite its peaceful nature, the sourcing, finicky feeding, surface-feeding, jump-risk and soft-water needs make it a fish for someone past their first tank.

Bringing one home

Quarantine new fish — nearly all are wild-caught and commonly arrive stressed and carrying internal parasites — and acclimate them gently into soft, acidic, tannin-stained, dimly-lit water. Be patient with first feeding: fresh imports often refuse dried food and need live or frozen surface foods (fruit flies, Daphnia, brine shrimp) to start before weaning onto flake. And make sure the lid is gap-free before the fish go in, since a startled new arrival is exactly when it jumps.

Common questions

Do marbled hatchetfish need a lid?

Absolutely — this is the most important thing about keeping them. They are the best jumpers of all the hatchetfishes, and leaping out to dry on the floor is the leading cause of death in captivity. You need a gap-free cover over the entire surface, with every cut-out for filters, heaters, cables and feeding flaps blocked. A "tight" lid with holes is not enough.

What do marbled hatchetfish eat?

They are obligate surface feeders that eat insects and small invertebrates from the top. Feed floating or slow-sinking flake and micropellet, plus live and frozen surface foods like brine shrimp, Daphnia, wingless fruit flies and mosquito larvae. They ignore food that sinks and won't scavenge the bottom, so in a tank of greedy mid-water feeders they can slowly starve.

How many marbled hatchetfish should I keep?

Six is the floor and ten or more is better. They are timid obligate shoalers — kept in small numbers they hide, stop feeding and fade, while a proper group is confident and uses the open surface.

Can marbled hatchetfish really fly?

Not in the storybook sense. They make a powered leap and glide along the surface on rigidly-held pectoral "wings," beating the fins at launch. Whether they truly flap in mid-air to power sustained flight is genuinely contested in the sources — so they're powerful jumping gliders, not flyers.

Are marbled hatchetfish good for beginners?

Not really, despite being peaceful. They are wild-caught and often finicky first feeders, need soft acidic blackwater, must be fed at the surface, and are serious jumpers needing a gap-free lid. They're best for someone past their first tank, kept in a calm, soft-water community with non-competitive tankmates.

Sources & confidence

Sources & confidence (9 species)

These back the Marbled Hatchetfish figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Marbled Hatchetfish Carnegiella strigata — Aquadiction / FishLore (Carnegiella strigata) high confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction high confidence
• Assassin Snail Clea helena (Anentome helena) — The Shrimp Farm (theshrimpfarm.com/posts/assassin-snail-care) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Bolivian Ram Mikrogeophagus altispinosus — Seriously Fish (seriouslyfish.com/species/mikrogeophagus-altispinosus) high confidence
• Bronze Corydoras Corydoras aeneus — Seriously Fish (seriouslyfish.com/species/corydoras-aeneus) high confidence
• Cardinal Tetra Paracheirodon axelrodi — Seriously Fish (seriouslyfish.com/species/paracheirodon-axelrodi) high confidence
• Celestial Pearl Danio Celestichthys margaritatus — Seriously Fish (seriouslyfish.com/species/celestichthys-margaritatus) high confidence

Care-guide sources (7)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• Seriously Fish — Carnegiella strigata (Marbled Hatchetfish) — family Gasteropelecidae, 30–35 mm SL, blackwater igapó/igarapé habitat, temp 20–28 °C, pH 4.0–7.0, hardness 18–179 ppm, 75×30 cm footprint, surface micropredator diet + live/frozen list, very peaceful but timid, shoal of 10 or more, tightly-fitting cover, breeding unrecorded, wild-caught (not commercially bred), possible species-complex
• FishBase — Carnegiella strigata (Günther, 1864) — family Gasteropelecidae, max 3.5 cm SL, temp 24–28 °C, pH 5.0–8.0, dH 5–19, feeds on crustaceans and insects, trophic 3.3, IUCN LC (2020), may jump out of the aquarium, eggs hatch ~36 h at 25 °C, ~80 cm tank for groups of five+
• Wikipedia — Freshwater hatchetfish (Gasteropelecidae) — enlarged sternal region + oversized pectorals, muscles ~¼ of body weight, quick pectoral beats to lift half out of the water and glide (powered-gliding framing, cites Frey 1961)
• Tropical Fish Hobbyist Magazine — Surface Dweller: hatchetfish — lives mere centimetres below the surface, lid absolutely paramount, powered-flight claim (flapping pectoral fins while airborne), travels >5 ft, pectoral muscles a major fraction of body weight, marbled lifespan under 2 years, ~1¾ in, pH 5.6–6.5, 74–80 °F
• Fishkeeping World — Hatchetfish / Marbled Hatchetfish — marbled ~1.75 in (4.4 cm), ~2 yr lifespan, 20-gal min, 74–80 °F, pH 5.6–6.5, 2–12 dKH, best jumpers of all the hatchetfish, tight lid, surface carnivore foods, peaceful but territorial with their own species, avoid bettas/tiger barbs/danios, breeding in soft acid water
• aqua-fish.net — Marbled Hatchetfish care guide — size 4–5 cm, temp 24–28 °C, pH 5.8–7.5, hardness 2–12 °dN, group 6+, lifespan 3–5 yr, surface insectivore + floating foods, peaceful shoaler, excellent jumpers (lid), females rounder, breeding hard
• Bird Flight: Hatchetfish (ornithopter.org) — documents the conflict in the literature on powered flight — some sources say it beats pectoral fins through the air, others that it skims the surface or merely leaps like any other fish; basis for treating mid-air flapping as contested

More on Marbled Hatchetfish

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →