Scaled, Armored or Naked: How Does the Skin of Fish Evolve?

The first vertebrates on the planet were most likely fish, appearing on earth million and millions of years ago. Over this vast period of time all the way to represent day they have changed drastically, whether that be externally or internally. If you have ever gone fishing or held a fish in your hands you know that they have a unique skin texture. Recently attention has been brought up about the 3 main different skin textures seen in fish and how they have evolved and changed over time through the gradual family tree of fish.

This attention has been recently been studied at the University of Geneva (UNIGE), Switzerland. This team of researchers have traced back the very first common ancestor of these vertebrates, and found it was the ray-finned fish. Studying the common ancestral tree they have come to find the three prominent skin textures are scaled, naked or bony armored plates. Most fish you see today are going to have the regular and most common scaled skin texture, but that does not include all the fish in the sea. Some examples of these other skin textures can be found in species of fish like the Placodermi, which now an extinct fish species but did have extremely hefty and bony armored plates. As for another example, a naked skin textured fish that is still alive today is the Astroblepidae, which is a rare freshwater fish that has a bare skin texture.

Surprisingly, common everyday fish like the catfish and goldfish make up the most diverse history of vertebrates in the world, since they are considered under the family tree of the Ray-finned fish. These species have far changed and spread their diversity creating thousands of different unique species. Comparing the main common ancestral tree containing roughly 11 thousand species and another common ancestral tree only containing 300 species, the team was able to make connections and infer that only fish that had lost their scales were able to develop and evolve into a bony armored skin texture. Also because of this evolutionary trait, they inferred that this protective state of the fish’s skin very heavily influenced the choices on where the fish made its habitat, in open water or more closely to the sea floor. Other evidence that was found shows that throughout the common ancestral tree many fish species lost their scales at different periods of time. Only being able to go from naked or scales to bony armored skin texture and not reversed, once a species has evolved and loses its scales it can not evolve back into a species that has scales. Genetic traits that came along with this transition including the select species of fish moving its habitat behaviors from open water to the sea floor or beds. These habitat movements are not only because of the likings of the fish but also because immune defense against viruses and bacteria were more effective against the fish when its skin was naked or had scales. Over time completing the complete circle as more and more species of fish chose the seabed it helped grow and nourish this area of diversity never seen before. That is why the ancestral family of the ray-finned fish is the biggest group of vertebrates on the planet.

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Biology Teacher

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