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Carnegiella strigata

Carnegiella strigata
Marble Hatchetfish
This species spends almost all of its time at the water surface, although it will sometimes retreat into midwater if threatened or feeding. Like other freshwater hatchetfish, it's renowned for its ability to fly for distances of several metres. This behaviour is used both to catch flying insects, and to escape potential predators. 
As well as giving rise to the common name, the strange shape of the fish is thought to be involved in the 'take-off' and 'landing' phases of flight, the trenchant belly stabilising the fish at it exits and re-enters the water. It also has specialised fins. The pectorals are enlarged, and have massive muscles attached to them, and the pelvics reduced. The pectoral fins are actually beaten in a similar way to the wings of birds or insects during flight, and an audible buzzing sound can often be heard as the fish moves through the air. The hatchetfish are the only known family of fish to employ powered flight, as opposed to the gliding behaviour seen in the marine flying fish. 
The marbled hatchet can be quite delicate when initially imported, but once acclimatised proves to be a very good aquarium resident. It can vary quite a bit in terms of colour and patterning, depending on collection locality. Some of these different forms were originally thought to be subspecies, but all are now classified as C. strigata . There are 3 other species in the genus, the most common of which in the hobby is the black-winged hatchet, C. marthae.