Marbled Gar (Boulengerella maculata)
Other common names for this fish: Spotted Gar or Spotted Pike Characin
Size is currently about 4-5 inches from tip of mouth to end of tail tip.
These fish do well in shoals/groups and tend to dwell on the upper levels of the tank. Be sure to house them with fish no smaller than them as they will inevitably become eaten by the Gar.
A well secured cover or lid is required as they can jump. They aren't brackish water fish though a tad bit of salt will be good for them.
Full size in aquaria is typically around one foot or so.
Though called a "Gar," it is closely related to Tetras as they are part of the Characin fish family.
Note: All true Gars are banned in the state of California but the Marbled Gar is an exception as it doesn't fall into the "true gar" family.