Bristlemouth Identification Guide

Key identification features

• Tiny, slender, elongated body, usually only 2 to 7 cm long
• Silvery sides fading to blackish-brown on the back, with thin or absent scales
• Disproportionately large mouth lined with fine, bristle-like needle teeth, giving the group its name
• Rows of small, bead-like photophores (light organs) running along the belly and lower sides
• Large, dark eyes relative to head size
• Single soft dorsal fin set roughly midbody, with a small adipose fin near the tail in many species

Common look-alikes

• Lanternfish (Myctophidae): also carry rows of photophores, but have a smaller mouth and a more robust, less needle-toothed jaw.
• Deep-sea hatchetfish: share ventral photophores, but have a strongly laterally compressed, hatchet-shaped body instead of the bristlemouth's slender, cylindrical form.
• Anglemouths and other stomiiform relatives: similar overall shape, but lack the extreme, gaping mouth-to-body ratio typical of bristlemouths.

Where you'll see one

Bristlemouths occur throughout the mesopelagic zone of every ocean basin, commonly between about 200 and 1,000 meters, and migrate toward the surface at night; because of their staggering numbers, they're often called the most abundant vertebrates on Earth.