How to Identify Pencilfish

To identify Pencilfish (Nannostomus), look at these key features.

Physical Characteristics

Body shape

elongated

Coloration

Highly variable depending on the species. Most species feature one to three prominent horizontal stripes running along the body, often in black, brown, or red, set against a base color of silver, gold, or reddish-brown. Many species exhibit sexual dimorphism, with males often displaying more intense coloration, especially during breeding, and sometimes having more elongated fins or specific color patterns (e.g., red on the anal fin).

Scale type

cycloid

Mouth position

superior

Distinctive features

Slender, cylindrical body shape, Small, upturned mouth, Often possess one to three distinct horizontal stripes, Adipose fin typically absent (present in some species, e.g., N. eques), Sexual dimorphism in coloration and fin shape in many species

Dorsal fin

Small, typically located mid-body, often with a dark spot or stripe.

Tail fin

Caudal fin is typically forked, sometimes with color patterns matching body stripes.

Pectoral fin

Small and transparent, positioned low on the body.

Distinctive fins

Pelvic fins are small. Anal fin is typically small, sometimes with species-specific coloration (e.g., red in male N. marginatus).

Identification Tips

1. 1

   Body Shape

   Look for a very slender, pencil-like body. This is a key characteristic that distinguishes them from many other small characins.

2. 2

   Mouth Position

   Observe their small, upturned mouth, which is adapted for feeding on small organisms at or near the water surface.

3. 3

   Stripe Patterns

   Pay close attention to the number, color, and arrangement of horizontal stripes. For example, N. trifasciatus has three distinct stripes, N. unifasciatus has one, and N. marginatus has a prominent dark stripe along the lateral line with red markings.

4. 4

   Fin Markings

   Some species have distinctive markings on their fins, particularly the dorsal, anal, and caudal fins, which can aid in identification (e.g., red spots or bands).

5. 5

   Swimming Posture

   Many Nannostomus species exhibit a characteristic head-up or head-down swimming posture, particularly N. eques (Hockeystick Pencilfish), which swims at an oblique angle.

Explore Pencilfish