Marble hatchetfish

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

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 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.

Origin and habitat

Native to forest streams and tributaries throughout the Amazon River basin in Colombia, Guyana, Suriname, Peru, and Brazil; also found in the Caquetá River system in Colombia. What is currently called C. strigata may represent a group of closely related species. Lives almost exclusively at the water surface, typically under dense floating vegetation or overhanging canopy in blackwater and clearwater systems. The genus Carnegiella was erected by C.H. Eigenmann in 1909 and honours Miss Margaret Carnegie, referring to the gracefulness of the fish. The species name strigata is Latin for "streaked". The deep, laterally compressed body is packed with enlarged pectoral muscles that power wing-like pectoral fins. Gasteropelecids are often described as the only true "flying" freshwater fish, capable of beating their pectoral fins to propel themselves through the air. Whether this constitutes powered flight or a powered launch followed by a glide remains debated. A tight-fitting lid is essential, as they jump readily and with considerable force. Gregarious and should be kept in groups of at least 6-8. Carnivorous surface feeders in the wild, taking crustaceans and insects; in captivity they do best with floating foods, frozen daphnia, and small insects. Many specimens in the trade are wild-caught.

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

Further reading

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