A Fishy Riddle

Like most riddles, the answer seems quite obvious once you’ve heard it: one fish is male, one fish is female, and one fish is a juvenile. That’s the answer in the case of Cetomimidae whalefish, which up until recently was only known for its female members.

Meanwhile, “seemingly related” species known as Mirapinnidae (“tapetails”) and Megalomycteridae (“bignose fish”) had been found, albeit only juvenile tapetails and only male bignose fish.

The skeletons of all three fish seemed to indicate that they were related—but there were “so many differences no one could believe they were the same fish at different sexes or stages in life,” explained David Johnson, an ichthyologist at the Smithsonian’s National Museum of Natural History. But “[t]he pieces kept falling into place,” he said.

The clue that confirmed Johnson’s suspicion was a DNA analysis that finally showed the three fish were the same species, despite the incredible differences in habitat and anatomy. For instance, juveniles live within 600 feet of the surface, while adults live thousands of feet below. Even stranger, while females grow expansive mouths to collect what little food is available, the male jaws fuse shut, and the males survive on energy stored up from their meals as larvae. Yet they develop oversized noses to help sense deep-sea smells.

While both evolutionists and creationists can explain sexual dimorphism (where males and females of the same species are distinct in size and anatomy), each case is nonetheless quite curious, and the Cetomimidae whalefish may be the most curious of all!