Veiled anglemouth, Cyclothone microdon.
Veiled Anglemouth, Cyclothone microdon

The veiled anglemouth is a truly cosmopolitan fish that inhabits mid to deep waters, ranging from 200–5000 m, in the oceans of the world. It is one of the most common fishes on the planet and, of all the fish in the deep Atlantic, over 80% of them are veiled anglemouths! This species is less dominant in the deep realms of the Pacific Ocean, where it comprises only 55% of individuals. With such a staggering abundance, it is no surprise that the veiled anglemouth is a significant component of the diet of many other fishes. It is also an important consumer of copepods, a diverse group of tiny crustaceans.

The veiled anglemouth, also known as the small-eyed lanternfish, is easily recognized by the patterning of its light organs – absent on the chin and between the gill openings, but present on the operculum, around the eye, the lower jaw, and in rows along its belly. Scales run along its lateral line, while black star-shaped pigment cells adorn its head, body, and fins.

The sex determination system in this fish is rather unusual; upon reaching a certain size, males often switch sexes to become females. Whether males undergo this sex reversal or not is dependent on the female density of the population – if females are rare, some males will make the switch. However, once a female, always a female; there is no turning back!