Examine the Clues

John Paxton, a scientist who studies marine life, looks into a microscope
Ichthyologist John R. Paxton of the Australian Museum identifies freshly caught lanternfishes. Paxton was on the team that solved the whalefish mystery. (R. Cornejo)

In 2003, a team of Japanese scientists analyzed the DNA of tapetails and whalefish. The results suggested that these two very different looking fishes were almost identical in one specific gene. But more clues were needed. An international team of marine biologists took a closer look at specimens of tapetails, bignose fish, and whalefish in museum collections. The team included Dave Johnson, an ichthyologist at the Smithsonian. Here’s what the team found.

  • Bignose fish have no throats or stomachs, but they do have enormous livers.
  • The immovable jaws of bignose fish could conceivably develop from the moveable jaws of tapetails.
  • Some tapetail specimens appear to be in the process of changing into bignose fish. With these and other clues from museum collections, scientists were able to crack the case.
The tapetail is the larva of the family. It transforms into either a male (bignose) or female whalefish.
The tapetail is the larva of the family. It transforms into either a male (bignose) or female whalefish. (Composite by Dave Johnson/Smithsonian Institution)

Aha! They’re All in the Family

It may be hard to believe because they look so different, but tapetails, bignose fish, and whalefish are actually all members of the same family (Cetomimidae).

  • Tapetails are the young, or larvae. They use their upturned mouths to gorge on small shellfish.
  • Bignose fish are the males. They feed off of their huge livers and use their large nasal organs to sniff for females.
  • Whalefish are the females. They use their gaping mouths to capture large prey.

There are other examples of males and females with very different shapes (sexual dimorphism) and of animals changing from one shape to another as they grow older (metamorphosis). But this is one of the most amazing examples of sexual dimorphism combined with metamorphosis ever found among vertebrates.


An image of collections storage at the Smithsonian National Museum of Natural History.
There are about 4 million specimens in the fish collection housed at the National Museum of Natural History. (Chip Clark/Smithsonian Institution)

Museum Collections Hold the Clues

“This is an incredibly exciting finding,” says Smithsonian ichthyologist Dave Johnson. “The answer to the puzzle was right under our noses all along—in the specimens. We just needed to study them more carefully.”

This scientific mystery clearly demonstrates the importance of museum collections. Many years after a specimen was collected, it may provide biologists with the answer to a new question raised by science. 

“The study also shows the need for continued exploration and collection in the open ocean—from the surface to the deep sea,” says Johnson. “Who knows what other mysteries remain to be solved there?”

August 2011