Marbled hatchetfish
The marbled hatchetfish ("Carnegiella strigata") is a small, normally in length, freshwater ray-finned fish native to South America. Hatchet shaped, it presents a gold line extending from its eye to its caudal fin while the area below has a brown and cream colored marble-like pattern (hence its name). In the aquarium. The marbled hatchetfish is common in the aquarium industry. Like most Amazonian fish, the species prefers softer, acidic water. As with most characins, they are omnivores. Hatchets have a tendency to be shy fish and are easily intimidated by larger or fast moving fish, so  they are only appropriate for very peaceful communities or species tanks. The marbled hatchetfish is usually kept in small schools. It is necessary for tanks inhabited by these fish to have a tight lid, as they can jump out when startled. Marbled hatchetfish are egg scatterers and have been bred in the aquarium hobby. Camouflage. Marbled hatchetfish are adapted to life in the Amazonian rivers as they resemble a dead leaf floating sideways on the surface of a body of water. This camouflage protects them against potential predators that may be lurking in the water. Their marble-like pattern is  to give the illusion of rays of light breaking the waters surface and reflecting on the portrayed leaf. The fish itself does not move much, letting the waves and currents move it mostly, but with occasional brief twitching movements. This replicates the way a leaf would be blown around or carried away by the tide or a current. The line running from its eye, to its tail, is believed to replicate the midrib (midvein) of a leaf.