Three Strange Fish, One Species

Jan. 22, 2009 -- Researchers believe they have solved the puzzle of three seemingly different fish, one all males, one all females and one all juveniles. They're the same fish, and undergo remarkable changes as they mature.

"You can imagine it was a pretty exciting discovery," said G. David Johnson, an ichthyologist at the Smithsonian's National Museum of Natural History. "The pieces kept falling into place."

"And it tells you how little we know about the deep sea, Johnson said in a telephone interview.

The fish live in the sparsely populated deep water thousands of feet below the surface, though as youngsters they rise to shallower levels where there is more to eat.

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Cetomimidae, a type of whalefish, had been known since the 19th century, but only females had been found.

Seemingly related species called Mirapinnidae, or tapetails, and Megalomycteridae, or bignose fish, were identified in the 1950s and 1960s. Tapetails were only found as juveniles and bignoses only as males.

Although their skeletons indicated the three were related, there were so many differences no one could believe they were the same fish at different sexes or stages in life, Johnson said.

But it turns out that is the case, Johnson and colleagues report this week in Biology Letters, a journal of Britain's Royal Society.

All three will now be classified as Cetomimidae, he said.

Johnson said the researchers were able to link the fish through comparative anatomical study and, once they obtained fresh samples, by their DNA.