Pencil fish

Lore & Background

The genus Nannostomus was first described by Günther in 1872, with the type species N. beckfordi. In 1876, Steindachner described three more species: N. unifasciatus, N. eques, and N. trifasciatus. In 1909, Carl H. Eigenmann described N. marginatus, N. minimus, N. erythrurus, and N. harrisoni. Several of these became popular with aquarists early in the 20th century, partly due to enthusiastic articles and photographs by William T. Innes published as early as 1933.

Over the years, the genus was split by subsequent authors into other genera, including Poecilobrycon and Nannobrycon. After nearly a century of debate, Dr. Stanley Howard Weitzman and Dr. J. Stanley Cobb restored earlier taxonomy and expanded upon it, unifying all species under Nannostomus in 1975. This revision has been widely accepted. Weitzman also described five more recently introduced species: N. marilynae, N. limatus, N. nitidus, N. britskii, and N. anduzei. Twenty species are now known, most familiar to aquarists, though several unidentified Nannostomus species have been imported as bycatch and their taxonomic status remains undetermined.

Reader's Guide

Pencil fish are significant in both ichthyology and the aquarium hobby. Their taxonomy was long debated, with the genus split into multiple genera before being unified by Weitzman and Cobb in 1975. This revision resolved nearly a century of confusion and is now widely accepted. In the aquarium trade, only two species—N. beckfordi and N. harrisoni—have been commercially raised, mostly in Asia; all others are wild-caught from South America. They thrive in soft, acidic water with low nitrates and temperatures of 22–28 °C, and benefit from planted tanks with floating plants to prevent jumping. They are hardy, often living five or more years, and should be kept in schools of at least six. Most species display horizontal stripes and red or orange fin highlights, with N. espei uniquely showing permanent dark comma-shaped blotches instead of stripes. Their peaceful nature and interesting behaviors, such as the 'snout-up' posture of N. unifasciatus and N. eques, make them enduring favorites among aquarists.

Did You Know?

• The name Nannostomus comes from the Greek nanos, meaning 'small', and the Latin stomus, relating to the mouth.
• All species swim horizontally except N. unifasciatus and N. eques, which assume an oblique, 'snout-up' posture.
• N. espei is unique in that its horizontal stripes are only weakly present and are replaced by five dark comma-shaped blotches, a pattern other species show only at night.
• The anal fin is generally a reliable indicator of gender; in most species, the anal fin of adult males is enlarged and elongated or more colorful.