The espei pencilfish (Nannostomus espei) is a small fish that is currently considered endemic to the Mazaruni River system in Guyana, including many of its tributaries such as the Kurupung, Eping, and Tabuba where it inhabits sluggish blackwater tributaries, small rivers and swampy areas, particularly in areas with dense growth of aquatic or overhanging riparian vegetation,  submerged woody structures and leaf litter.  The water is typically stained darky with humic acids and other chemicals released by decaying organic material, the dissolved mineral content is generally negligible and the pH can be as low as 4.0.  This fish grows to an adult size of just over an inch long.  Mature females are noticeably more stocky and rounded and often a little larger than the males.  Adult males are more intensely patterned and have more color in the fins.

Espei pencilfish should be maintained in an aquarium of 20 gallons or larger.  A soft, sandy substrate (CS7538) is a good choice.  Driftwood (ZM2000) and  live or artificial plants may also be incorporated.     

Espei pencilfish prefer a temperature of 72°F to 82°F, a pH of 4.0 to 6.5, and a hardness of 2 to 15°H.  Be sure water is clean and well oxygenated.  

The espei pencilfish is a very peaceful fish well suited to a planted aquarium.  Good tank mates include small tetras, livebearers, danios, rasboras, cory catfish, loricariid catfish, and dwarf cichlids.  Keep them in groups of 6 or more.

Marginated pencilfish are easy to feed fish accepting almost any appropriately sized food offered.  In the aquarium they will readily accept flakes (AL165) and small frozen foods.  For maximum color, growth, and health these fish will look their best when given probiotics (AL169) in addition to a balanced diet.