How to Identify Diaphanous Hatchetfish

To identify Diaphanous Hatchetfish (Sternoptyx diaphana), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Silvery, often with iridescent reflections, particularly on the flanks. The dorsal surface can be darker, while the ventral side is typically lighter, aiding in counterillumination. The body is largely translucent, especially in smaller individuals.

Scale type

none

Mouth position

terminal

Distinctive features

Extremely deep and laterally compressed body, resembling a hatchet., Large, upward-pointing tubular eyes, adapted for detecting silhouettes against the faint downwelling light., Well-developed ventral photophores (light-producing organs) arranged in complex patterns, used for counterillumination., Small mouth, typically terminal or slightly superior., Absence of scales, or very minute, deciduous scales that are easily lost during capture.

Dorsal fin

Single dorsal fin, typically small, located posteriorly. Often preceded by a small adipose fin.

Tail fin

Forked caudal fin, moderately sized.

Pectoral fin

Pectoral fins are small to moderately sized, positioned low on the body.

Distinctive fins

Pelvic fins are small and located abdominally. An adipose fin is present.

Identification Tips

1. 1

   Body Shape

   Look for the extremely deep, laterally compressed body that gives it a distinct hatchet-like profile.

2. 2

   Eyes

   Observe the large, tubular eyes that are directed upwards, a key adaptation for deep-sea vision.

3. 3

   Photophores

   Identify the rows of ventral photophores, which are light-producing organs used for camouflage (counterillumination). The specific arrangement can help differentiate species within Sternoptyx.

4. 4

   Size

   Adults typically reach a maximum standard length of about 5-6 cm (2-2.4 inches).

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