Solved puzzles about deep-sea fish teeth

Special nanostructure makes subsea of ​​deep-sea dwellers transparent

The teeth of the deep-sea fish Aristostomias scintillans remain invisible to potential victims. © David Baillot / UC San Diego Jacobs School of Engineering
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Invisible weapons: Researchers have discovered why the teeth of some deep-sea fish appear transparent. The secret lies in the special nanostructure of the biter. It ensures that the teeth of the deep-sea dwellers are transparent and remain invisible even when light falls in the dark environment - a decisive advantage in prey hunting. This patent could serve as a model for new transparent materials in the future.

The deep sea is a place of eternal darkness - and the home of truly bizarre creatures: Hundreds of meters below the surface of the sea fish live with huge eyes, grimacing faces and disproportionately large mouths that attract their prey with self-generated lighting effects. Aristostomias scintillans from the Barten-Drachenfische family belongs to these strange robbers.

These only about 15 centimeters long deep-sea fish are among the top hunters in their area and have another special feature: Their teeth are not white, but transparent. "Some other deep-sea fish also have this interesting feature. How it's done has never been researched, "said Audrey Velasco-Hogan of the University of California at San Diego and her colleagues.

Dangerous weapons

To find out more about the bites of the dragonfish, the scientists have now taken a closer look at them. The first tests were a surprise: The teeth of A. scintillans are extremely hard and sharp and thus similar dangerous as that of notorious predatory fish such as the Great White Shark or Piranhas.

But how does the transparency of the teeth come about? Investigations using, among other things, electron microscopy revealed that the tooth structure of the fish is at first glance comparable to ours. Accordingly, the Bei er consist of an outer enamel and an inner dentin layer. display

Nanostructure ensures transparency

The special feature, however: both layers contain nanocrystals of hydroxyapatite. In enamel, these minicrystals are scattered and present in a size of about 20 nanometers. In the dentin, however, the hydroxyapatite coats collagen fibrils and together with them forms tiny stabs with a diameter of about five nanometers. Microscopic microstructure structures that affect color in human teeth, for example, lack the dentine, the researchers found.

According to them, this special nanostructure ensures that the teeth barely reflect or scatter incident light. This effect is strengthened by the fact that the animals of the dragonfish are very thin. "Normally, teeth are not nanostructured, " says Velasco-Hogan. "From a material science point of view, it is very interesting that the architecture of the dragonfish teeth is so different from what we know from most other animals."

Well camouflaged

But why did A. scintillans and some of the other inhabitants of the deep sea ever develop transparent insects in the course of evolution? The scientists suspect an advantage in prey hunting: Many creatures in the deep sea can produce light to navigate, confuse enemies or attract victims - even the dragonfish uses this strategy. "But the teeth of this fish are very large in proportion to its mouth. If they become visible, any prey animal would flee immediately, "explains Velasco-Hogan's colleague Marc Meyers.

Thanks to their special structure, however, the teeth of the robber remain hidden despite the light effects and do not contrast with the surrounding water. "In combination with the black skin, the sharp teeth thus form a deadly, invisible weapon, " the scientists summarize.

Model for new materials?

As the research team emphasizes, the study not only provides new insights into the biology of the mysterious deep-sea dwellers. It may also be possible to develop new tarnsparent materials on the model of the dragonfish. "Studying and using the adaptations of organisms to specific environments has always been a driver of technological innovation. The dragonfish is no exception, "concludes Velasco-Hogan's colleague Dimitri Deheyn. (Matter, 2019; doi: 10.1016 / j.matt.2019.05.010)

Source: Cell Press / University of California San Diego

- Daniel Albat