Photocorynus
Deep-sea anglerfish with the smallest known mature males
Photocorynus is a genus of deep-sea anglerfish containing only one species, Photocorynus spiniceps. First described in 1925, these fish live in the Atlantic and Pacific oceans at great depths. They are notable for extreme sexual dimorphism, where tiny males fuse permanently to much larger females.
- Males are the smallest known mature vertebrates at under 8 mm
- Males fuse permanently to females for reproduction
- Uses a bioluminescent sac to lure prey in deep water
- Found in Atlantic and Pacific oceans at depths over 900 m
What it is
Photocorynus is a monospecific genus of marine ray-finned fish in the family Linophrynidae, known as leftvents. The single species is Photocorynus spiniceps. These are deep-sea anglerfishes belonging to the suborder Ceratioidei. The genus name means light club, referring to the glowing sac on its lure. The species name means spiny head, describing robust spines on the sphenotic bone. Females grow up to 50.5 millimetres, while mature males are only 6.2 to 7.3 millimetres long. This makes the male the smallest known mature vertebrate.
Where it lives
This species has a circumglobal distribution across the Atlantic and Pacific Oceans. In the Atlantic, records exist from both sides between 32 degrees north and 13 degrees south. In the Pacific, it has been found near Japan, Hawaii, and the Gulf of Panama. Specimens are collected from depths ranging from 990 to 1,420 metres. The holotype was originally taken from the Gulf of Panama at a depth of approximately 1,250 metres.
How it lives
Like other deep-sea anglerfishes, it uses a bioluminescent sac at the end of its illicium to attract prey. The illicium is a highly modified first ray of the dorsal fin. It swallows prey whole using a distending jaw and stomach. Prey items can be as large as the fish itself. The male spends its entire life fused to a much larger female. He bites her to attach permanently, effectively turning her into a hermaphrodite. The female handles swimming and feeding while the male focuses on reproduction.
Breeding and life cycle
Reproduction involves permanent physical attachment between the sexes. The male bites the female and fuses with her body for the rest of his life. A large proportion of the male body consists of testes. His primary role is aiding reproduction while attached to the female. The female continues to swim and eat independently. This extreme form of sexual dimorphism ensures the male is always available for spawning when the female is ready.
Fish and people
The genus was first proposed in 1925 by English ichthyologist Charles Tate Regan. He described the only species, P. spiniceps, based on a holotype collected by the Danish research vessel Dana. These fish are primarily of interest to scientific research due to their unique biological traits. They hold records for the smallest mature male vertebrates.
Status and threats
As a deep-sea species living at depths over 900 metres, it is likely less exposed to surface-level human activities.
Questions people ask about Photocorynus
How small are the male Photocorynus fish?
Mature male individuals measure between 6.2 and 7.3 millimetres in length. This size makes them smaller than any other known mature fish or vertebrate species. In contrast, females can grow up to 50.5 millimetres long.
How do Photocorynus reproduce?
The male bites the female and fuses his body to hers for life. This attachment turns the pair into a functional hermaphrodite unit. The male provides sperm while the female handles swimming and feeding duties.
Where does this fish live?
It lives in the deep ocean waters of the Atlantic and Pacific Oceans. Specimens have been recorded at depths between 990 and 1,420 metres. Specific locations include the Gulf of Panama, Japan, and Hawaii.
Good reading and sources
The facts on this page come from the Wikipedia article "Photocorynus", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.
It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.
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