The deep-sea fanfin anglerfish uses independent, glowing filaments to hunt in total darkness

Nature · Published 3 October 2026 Swipe more like this →

In short: Living 2,600 feet below the North Atlantic, the fanfin sea devil is a master of the abyss. Unlike other fish, its bioluminescent fin-rays move independently, each controlled by its own dedicated muscle and nerve network. This unique adaptation helps the anglerfish survive in an environment where food is incredibly scarce.

The fanfin sea devil, or Caulophryne jordani, belongs to a group of deep-sea anglerfish that thrive in the aphotic, high-pressure zones of the world's oceans. While there are over 162 species of deep-sea anglerfish, the fanfin is distinguished by its wispy, whisker-like filaments. These structures are not merely decorative; they are sensory tools that emit bioluminescent light, allowing the fish to detect prey or potentially mimic dangerous jellyfish to deter predators.

The mating strategy of these creatures is among the most extreme in the animal kingdom. Male fanfins are significantly smaller than females and possess highly developed eyes and nostrils to track chemical signals released by their mates. Upon locating a female, the male bites down, initiating a process where their tissues and circulatory systems fuse. The male then becomes a permanent sexual parasite, losing his own organs and fins to serve as a lifelong sperm bank nourished by the female's blood.

Observing these fish in their natural habitat is exceptionally rare, as they cannot survive the pressure and temperature changes involved in laboratory study. In August 2016, researchers captured the first known footage of a live fanfin near Portugal's São Jorge Island. This encounter provided scientists with a rare window into their behavior, revealing that their glowing filaments function as individual units rather than a single connected membrane, a feature never before documented in any fish species.

While the fanfin is known for this parasitic behavior, evidence suggests it may be facultative, meaning it is not strictly required for the survival of the species. Some specimens of C. jordani have been found with mature ovaries despite lacking an attached male. As research continues, scientists hope to better understand how these elusive predators navigate the extreme conditions of the bathypelagic zone, where every missed meal represents a significant survival risk.

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