Nannostomus (from the Greek nanos = small, and the Latin stomus = relating to the mouth)[1] is a genus of fish belonging to the characin family Lebiasinidae.

[1][2][3] Several species have become popular aquarium fish due to their attractive coloration, unique shape, and interesting demeanor.

Several other unidentified Nannostomus species have been imported over the years; many were found as bycatch with other small characins, but their taxonomic status is yet to be determined.

N. marginatus, N. rubrocaudatus, and N. mortenthaleri possess shortened, blockier outlines reminiscent of pencil stubs.

N. espei is unique in that the horizontal stripes are only weakly present and are supplanted by five dark comma-shaped blotches.

To date, only two species, N. beckfordi and N. harrisoni, have been commercially raised for the aquarium trade in fisheries, mostly in Asia.

Nannostomus species thrive in home aquaria when provided with soft, moderately acidic water, low nitrate levels, and temperatures in the range of 22–28 °C (72–82 °F).

The addition of aquatic plants is recommended, including floating varieties as they reduce the likelihood of fish jumping, a common occurrence for some of the species, especially N. espei and N. unifasciatus.

Baby brine shrimp, live or frozen, and other small-sized foods are required for both fry and adults.

Their defensive actions are usually harmless, but in two species, N. mortenthaleri and N. trifasciatus, antagonistic behavior directed at conspecifics can be harmful if sufficient space and plant cover is not provided.