Tiny Danionella dracula fish has tooth-like fangs

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Scientists, including two Practical Fishkeeping contributors, have described bizarre and previously unseen adaptations in a new species of miniature cyprinid from Myanmar.

Males of the tiny cyprinid species, which is known only from a small stream in northern Myanmar (Burma), have enormous tooth-like fangs which look like canine teeth, projecting through the skin of their mouths.

The tiny fish is the only known species from the 3700-strong cypriniform group to have evolved the trait, and has been named Danionella dracula after its resemblance to the famous Count of Bram Stoker's novel.

Ralf Britz and Lukas Ruber of the Natural History Museum, London, and Kevin Conway of Saint Louis University, who named the new species in a paper to be published in the journal Proceedings of the Royal Society B later today, said that the new fish represented one of the "most developmentally truncated vertebrates."

Developmental truncation

Like other members of the Danionella genus, the species is incredibly small and is believed to be fully-grown at just 16.7mm long.

It looks very much like the tiny fry of a larger species, with a transparent body and very small size, much like other described Danionella, such as D. translucida and D. mirifica. However, neither of its relatives show the degree of skeletal modification seen in D. dracula.

"Forty-four bones or parts thereof fail to develop in D. dracula, compared with its close relative Danio rerio, which is roughly twice its length," the authors wrote.

"Our analysis shows that with few exceptions the missing bones in D. dracula are those that ossify late in the onotogenetic trajectory of the zebrafish.

"Their lack in D. dracula thus suggests a relatively simple case of developmental truncation, ie. a loss of terminal stages of ontogeny."

However, there are also a number of other bones that aren't explained by truncation of development - something seen in other miniature cyprinids - which may suggest evolutionary links between the species.

Fangs

In previous studies, the authors have provided unexpected evidence to suggest a link between developmentally truncated miniatures - that is, adult fish that resemble fry - and the evolution of morphological novelties.

The unusual tooth-like fangs of Danionella dracula appear to provide further weight to their theory.

Although they look like teeth, these fangs are actually not true teeth. They lack an enamaloid cusp and a pulp cavity, and they're much more prominent in males of the species than they are in females.

"The fangs and processes in D. dracula are not true teeth. Their condition is, however, still more similar to that of toothed jaws than in any other cypriniform.

"The newly discovered species D. dracula is morphologically closer to an oral dentition than any other cypriniform, but with the evolutionary acquisition of its odontoid processes, it has clearly followed an alternative route to the re-evolution of jaw teeth. "

For more information see the paper: Britz R, Conway KW and L Ruber (2009) - Spectacular morphological novelty in a miniature cyprinid fish, Danionella dracula n. sp. Proceedings of the Royal Society B. doi:10.1098/rspb.2009.0141