I think there proper name is Silver Hatchett.
There from south America and grow to 3 inches, they like acid nuetral water and are carnivorous.
They are top dwellers andlike a 6-12 dh.
Keep the aquariam covered as they are good jumpers.
I think they're actually related to tetras so would be best kept in a school. I had six marbled hatchets in my tank but I lost 2 to jumping, so beware as they are very good jumpers!
Definitely keep them in groups, they are actually a bit less jumpy that way, floating plants like duckweed also keep them in the water a bit better. A tight fitting cover is a must.