How to Identify Butterfish

To identify Butterfish (Pholis gunnellus), look at these key features.

Physical Characteristics

Body shape

eel-like

Coloration

Highly variable, ranging from yellowish-brown to reddish-brown or olive-green, often mottled or barred to blend with its surroundings. The ventral side is typically paler. The most distinctive feature is a series of 9-16 (usually 9-13) black, white-ringed ocelli (eye-spots) along the base of the dorsal fin.

Scale type

none

Mouth position

terminal

Distinctive features

Eel-like, elongated body, Smooth, scaleless skin (or very small, embedded scales), Long dorsal fin extending from head to tail, Series of black, white-ringed ocelli along the dorsal fin base, Small, rounded pectoral fins, Pelvic fins are greatly reduced or absent

Dorsal fin

Very long, continuous dorsal fin extending from just behind the head to the caudal fin, composed entirely of flexible spines (typically 75-90).

Tail fin

Small, rounded caudal fin, confluent with the dorsal and anal fins.

Pectoral fin

Small and rounded, located just behind the operculum.

Distinctive fins

Anal fin is also long, extending from mid-body to the caudal fin, composed of 1-2 spines and 39-47 soft rays. Pelvic fins are either absent or represented by a single, minute spine.

Identification Tips

1. 1

   Body Shape

   Look for a very slender, eel-like body, not flattened like a flatfish or robust like a cod.

2. 2

   Dorsal Fin Spots

   The most reliable identifier is the row of distinct, black, white-ringed spots (ocelli) along the base of the dorsal fin. Count them; there are typically 9-13.

3. 3

   Skin Texture

   The skin appears smooth and slimy, lacking prominent scales.

4. 4

   Fin Structure

   Note the continuous dorsal and anal fins that merge with the caudal fin, and the very small, rounded pectoral fins.

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