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 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.

Origin and habitat

Carnegiella strigata, the marbled hatchetfish, is a small surface-living characin in the family Gasteropelecidae. It is widespread in northern South America, through the Amazon and Orinoco drainages and the coastal rivers of the Guianas, and lives in soft, acidic blackwater streams beneath overhanging vegetation, among fallen branches and leaf litter. What goes by the name C. strigata may in fact be a cluster of closely related species. Eigenmann erected the genus Carnegiella in 1909, naming it for Margaret Carnegie and meaning to capture the fish's gracefulness, while the species name strigata means streaked, for the dark marbling on the deep, keeled flanks. That deep belly houses unusually large muscles that drive wing-like pectoral fins. Hatchetfishes are widely called the only true flying fish, since they are the only fish that move their pectoral fins to power flight, though whether this is true flapping flight or a powered launch followed by a glide is still argued. Either way they leave the water with real force, which makes a tight lid essential. They are gregarious surface feeders, best kept in groups of six or more, and many in the trade are still wild-caught.

Breeding

Breeding in aquaria is difficult and seldom managed. The fish are egg scatterers that spawn among fine-leaved or floating plants near the surface, and the few accounts point to very soft, acidic water and dim light, often after a big water change, as the trigger. Reported clutches are small and the eggs are sensitive to light. Sexing is hard, with females perhaps a little fuller. Because no dependable method has taken hold, wild collection still supplies most of the trade.

Common problems

Jumping is what kills most marbled hatchetfish. They launch when startled, at night, and sometimes for no clear reason, so every gap around tubing, cords, and the lid is an escape route, and fish on the floor are the classic loss with this species. Turning on the room light before the tank light helps avoid panic leaps. New fish, especially wild-caught ones, often arrive with ich, which the species handles well under heat treatment, and wild stock can carry internal parasites that cause wasting. A thick film of surface scum blocks their feeding zone, so a little surface movement to keep the top clean helps. As timid fish, they retreat and stop feeding if kept with boisterous or aggressive tankmates.

Bioload

Further reading

• Stocking ideas by tank size