Carnegiella strigata, the Marbled Hatchetfish

Carnegiella strigata (Marbled Hatchetfish). There are two populations, sometimes considered subspecies of this surface-hugging hatchetfish that escapes its enemies by flying across the water surface; one is  from forest pools and small side streams in the stretch of the upper Amazon where Peru, Colombia and Brazil come together, the other from Guyana and Suriname. In many locations in the mid Rio Negro basin they occur sympatrically with no less than three cryptic species of Carnegiella marthae. Every aspect of their structure identifies them as fishes that haunt the surface. In natural surroundings most of their food consists of hapless insects that have fallen on the water and the smallest water-dwelling crustaceans. So, though they're very good about eating floating flake food, they'll thrive better if you supplement the flakes with some freeze-dried bloodworms or daphnia, or some live fruit flies.
 
They're uneasy kept in solitude; keep half a dozen together.  They love some current and will hang out together in the filter outflow, which, however, they may think is a fish ladder to more interesting territory upstream. You know what jumpers the hatchetfish are; sometimes they have been called "freshwater flying fish." Whether or not they vibrate their pectoral fins in flight has been mooted about; recently high-speed video seems to have established that the flight is a guided jump, a modified startle response. If you're keeping hatchetfish, drop your water level several inches to give them some headroom, and give them some reassuring floating plant cover, using Water Sprite, for example. With the security of shade, they'll show more subtle tints in their scheme of silver bellies shading to olive-brown backs overlaid with dark streaks and marbling. I generally leave my tanks alone as much as I can, keep my paws out of the water and let them get on with whatever they're doing, but fishes that jump out at the first opportunity, before I even do anything to alarm them... well they make me skitterish too.
 
Nobody around here seems to breed hatchetfish consistently, and in the U.S. we still rely on wild-caught stock, though Singapore supplies European fishkeepers.
 
Links. Carnegiella strigata species profile at Microcosm: Aquarium Explorer. Species profile of Carnegiella strigata at Tropical Fish Hobbyist. Species profile at SeriouslyFish. 
 
Carnegiella strigata at FishBase. Carnegiella strigata at Wikipedia. And see a YouTube video of Carnegiella strigata enjoying the current from the filter outflow.