Freshwater hatchetfish
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[Photo] Blackwinged hatchetfish, Carnegiella marthae. Date 14 March 2006. Author Tsunamicarlos

The freshwater hatchetfishes are a family, Gasteropelecidae, of ray-finned fish. The common hatchetfish is the most popular member among fish keeping hobbyists. The family includes three genera: Carnegiella (4 species), Gasteropelecus (3 species), and Thoracocharax (2 species).

Distribution and habitat
Freshwater hatchetfishes originate from Panama and South America (though it is absent in Chile). They tend to be a upper-level fish, often swimming directly below the surface of the water.

Flight
The most obvious trait of the freshwater hatchetfish is their enormously enlarged sternal region. This is accompanied by large pectoral fins and massive associated muscles. Due to this, they are the only fish technically enabled for powered (as opposed to gliding, as in flyingfish) flight, although the exact degree to which this mechanism is actually used is not well researched. They can propel themselves out of the water and at least assist their flight by rapidly striking their pectoral fins to evade predators, albeit only for distances of a few meters and in a straight line. Alternatively, they can make shorter flying jumps to catch insects. Because of this ability to "fly", or at least this tendency to jump, when kept in an aquarium the cover should be tight and sealed to prevent these fish from escaping.

Genera and species

Genus Carnegiella (Eigenmann, 1909)
Blackwinged hatchetfish, Carnegiella marthae
Pygmy hatchetfish, Carnegiella myersi
Dwarf hatchetfish, Carnegiella schereri
Marbled hatchetfish, Carnegiella strigata

Genus Gasteropelecus (Scopoli, 1777)
Silver hatchetfish, Gasteropelecus levis
Spotted hatchetfish, Gasteropelecus maculatus
Common hatchetfish, Gasteropelecus sternicla

Genus Thoracocharax (Fowler, 1907)
Greater hatchetfish, Thoracocharax securis
Spotfin hatchetfish, Thoracocharax stellatus

http://en.wikipedia.org/wiki/Freshwater_hatchetfish

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