Sloane's Viperfish Identification Guide

Key identification features

• Slender, laterally compressed body, dark silvery-black with a metallic sheen
• Extremely long, needle-thin fangs so large they cannot fully close inside the mouth, curving outward past the eyes when the jaw shuts
• First dorsal fin ray greatly elongated into a thin filament tipped with a light-producing lure, held forward over the head
• Large eyes adapted for extremely low light
• Rows of small photophores running along the belly and lower sides
• Moderate size, generally reaching about 25 to 30 cm

Common look-alikes

• Other Chauliodus species: nearly identical in shape and fang size, distinguished mainly by subtle differences in dorsal fin ray counts and photophore arrangement.
• Loosejaws (Malacosteus, Aristostomias): also fanged and dark-bodied, but lack a skin floor under the lower jaw and lack the elongated luminous dorsal lure that viperfish carry.
• Fangtooth (Anoplogaster): shares oversized teeth, but has a much deeper, compact body instead of the viperfish's slim, elongated profile.

Where you'll see one

Sloane's viperfish occurs in tropical and temperate waters of every major ocean, living in the mesopelagic zone below about 1,000 meters by day and migrating upward toward roughly 200 meters at night to feed.