Marble hatchetfish

Quick facts

Adult size

4 cm

Lifespan

can live up to 5 years

Tank zone

top

Temperament

peaceful

Difficulty

intermediate

Schooling

recommended 6+ (critical minimum 4, thrives at 10+)

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

24–28°C

pH

5.5 to 7.0

Hardness

1 to 10 dGH

Tank requirements

Minimum volume

80 L

Minimum length

60 cm

Flow

low

Lighting

dim preferred

Substrate

any

Open swimming room

needed

Lid

required - jumper

Feeding

Diet: carnivore, feeds primarily at the top.

Surface feeder that takes food from the water surface film. Flake food is ideal because it floats. Floating micro pellets, freeze-dried bloodworm, and live food that stays at the surface (fruit flies, mosquito larvae, small crickets) are all accepted. They won't eat food that has sunk below the top few centimeters. In community tanks, make sure floating food isn't stripped by midwater fish before the hatchetfish can eat. Feed twice daily. Live food triggers the strongest feeding response. A wingless fruit fly culture is an excellent long-term food source.

Compatibility

• Strict surface-dweller. Hatchetfish occupy the top centimeter of the water column and rarely descend. This means they occupy a zone that most other fish ignore, making them compatible with a wide range of midwater and bottom species.
• Peaceful and timid. Avoid boisterous surface-feeding species that would outcompete them. Good companions: small tetras, rasboras, corydoras, and otocinclus that stay in lower zones.
• Notorious jumpers. The deep, keeled body is adapted for powered flight (they actually beat their pectoral fins, they don't just glide). A tight lid is the single most important piece of equipment for a hatchetfish tank. Without one, you'll lose fish.
• Groups of 6+ are necessary. Solitary hatchetfish hide and refuse food. In a group, they hover at the surface in a loose school and are more confident.

Habitat

Native to blackwater streams and flooded forest areas in the Amazon basin, primarily in Brazil, Peru, and Guyana. Found at the surface among floating vegetation and overhanging bankside plants. The species (Carnegiella strigata) is the most commonly available hatchetfish in the hobby. The body shape is unique among aquarium fish: a deep, compressed body with a prominent ventral keel (the 'hatchet' shape) that houses enlarged pectoral muscles. These muscles power true flight: when startled, hatchetfish launch from the water and beat their pectoral fins to travel several feet through the air. This is not gliding; it's powered flight, making them one of the only flying freshwater fish. The body is olive to silver with a marbled pattern of dark brown lines and spots. Adult size is about 3.5–4 cm. Both wild-caught and commercially bred specimens are available. The species has been in the trade since the 1930s but has never achieved mass popularity, partly because they're surface-only fish that don't interact much with the rest of the tank.

Breeding

Rarely bred in home aquariums. The specific triggers for spawning are poorly understood. Occasional reports describe egg-scattering among floating plant roots in very soft, acidic water (pH below 6, GH below 3) after significant water changes. Clutch sizes are reportedly small. Eggs are light-sensitive. Sexing is difficult; females may be slightly fuller-bodied. The difficulty of breeding contributes to continued wild collection for the trade. No reliable, repeatable home breeding protocol exists in the hobby literature. Commercial breeding may occur on a small scale in specialized facilities but wild-caught fish dominate the supply.

Common problems

Jumping is the primary cause of loss. Hatchetfish jump when startled, during the night, and sometimes for no apparent reason. Every gap in the lid is a potential escape route. Cover all openings around filter tubing, heater cords, and airline. Hatchetfish found on the floor are one of the most common losses reported by keepers of this species. Ich is common in newly purchased fish, especially wild-caught specimens. Treat with temperature elevation; the species tolerates heat treatment well. Wasting from internal parasites (wild-caught specimens) is the other major health concern; treat with praziquantel. Surface scum from protein buildup blocks their feeding zone; maintain surface agitation to prevent a thick biofilm layer from forming on the water surface. Stress from aggressive or boisterous tankmates causes permanent hiding behavior.

Bioload

Bioload coefficient: 1.0 (tiny surface-dwelling fish; negligible waste).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size