"In dogs, that was the result of selective breeding," Lundberg said. "In Kryptoglanis, we don't know yet what in their natural evolution would have led to this modified shape."
The researchers seem to have ruled out the possibility that the catfish's unusual mug resulted from a highly specialized diet. That's because, based on the fish's teeth and subterranean habitat, it most likely eats a relatively typical diet of small invertebrates and insect larvae, Lundberg said. Video footage of live specimens at feeding time also suggests that this tiny fish — at 4 inches (10 centimeters), it's smaller than the average adult's pinky finger — is perfectly capable of eating such food.
The mystery of Kryptoglanis has received attention from other researchers, as well. Ralf Britz, a fish researcher at the Natural History Museum of London, led a separate study of the species' unique bone structure. The research was published in the March 2014 issue of the journal of Ichthyological Exploration of Freshwaters.
Unlike Lundberg's study, which used high-resolution X-ray computed tomography to create three-dimensional CAT scan images of the fish's skeleton, Britz and his team utilized a technique known as clearing and staining. This method of visualizing a skeleton uses chemicals to render the fish's soft tissues in clear glass and its bones and cartilage in contrasting, colored glass.
Yet, much about the catfish remains mysterious. For instance, neither study was able to definitively conclude why Kryptoglanis is so unique among fishes, or what species it counts as its closest relatives.
The new study, led by Lundberg, is published in the 2014 issue of the Proceedings of the Academy of Natural Sciences of Philadelphia.
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