Fish
Whalefish
Cetomimidae · also called flabby whalefish
So different between the sexes that scientists once believed they belonged to three separate fish families entirely, a whalefish quietly rewrote its own taxonomy once DNA evidence revealed male, female, and juvenile to be the very same species.
Overview
The whalefish, family Cetomimidae, is a soft-bodied deep-sea fish native to deep ocean habitat recorded across every major ocean basin. Its extraordinary history of mistaken taxonomic identity, extreme differences between males and females, and males’ complete abandonment of feeding as adults make it one of the most scientifically surprising fish families found anywhere in the deep sea.
A taxonomic mystery solved by DNA
For years, the dramatic differences between whalefish males, females, and juveniles led researchers to place them in entirely separate families, a mistake only corrected once genetic evidence proved beyond doubt that all three were simply different life stages of the very same fish.
Status
Least Concern, though detailed population trends remain largely unknown given the difficulty of surveying deep ocean habitat.
Whalefish: common questions
Why were whalefish once classified as three different families?
This family shows extreme sexual dimorphism, and historically scientists mistook males, females, and juveniles for entirely separate fish families before later evidence revealed them to be the same fish at dramatically different life stages.
Do male whalefish eat as adults?
No, adult males in this family lack a functioning digestive system entirely, surviving only on energy reserves built up earlier in life, with their sole remaining purpose being to locate a female and reproduce.
What does a whalefish's body feel like?
This family has a notably soft, flabby, gelatinous body, an adaptation suited to withstanding the immense pressure found throughout its deep-sea habitat.
How different do male and female whalefish look?
Dramatically different, with females far larger and equipped with a functioning digestive system, while males remain tiny throughout their short adult lives and never develop a working gut.