How to Identify Pygmy Killifish

To identify Pygmy Killifish (Heterandria formosa), look at these key features.

Physical Characteristics

Body shape

elongated

Coloration

The body is typically olive-brown to yellowish-tan dorsally, fading to a lighter, often silvery, ventral surface. A prominent dark lateral stripe runs from the snout through the eye to the caudal peduncle, often broken into a series of blotches or spots. Males may exhibit iridescent blue or green flecks, especially during breeding. The fins are generally clear or slightly yellowish.

Scale type

cycloid

Mouth position

superior

Distinctive features

Extremely small size (females up to 3 cm, males up to 2 cm), Prominent dark lateral stripe, often broken, Sexual dimorphism: females are larger and rounder, males are smaller with a modified anal fin (gonopodium), Livebearer (gives birth to live young)

Dorsal fin

Single, relatively small dorsal fin positioned posteriorly, typically with 6-8 rays.

Tail fin

Rounded to slightly truncate caudal fin.

Pectoral fin

Small, clear pectoral fins.

Distinctive fins

Males possess a highly modified anal fin called a gonopodium, used for internal fertilization. Females have a fan-shaped anal fin.

Identification Tips

1. 1

   Size

   Its exceptionally small adult size (females rarely exceed 3 cm) is the most immediate identifying feature.

2. 2

   Lateral Stripe

   Look for the distinctive dark lateral stripe, which can be continuous or broken into a series of blotches, running along the side of the body.

3. 3

   Mouth Position

   The upturned (superior) mouth is indicative of its surface-feeding habits.

4. 4

   Sexual Dimorphism

   Observe the difference in size and fin structure between sexes; males are smaller and possess a gonopodium.

Explore Pygmy Killifish