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Like most fish species, wild carps have scales, which give them external protection all over their body (bottom picture). During the domestication of the carp, a “mirror” mutant with few scales (top picture) was selected by fish farmers. Some of these were introduced in Madagascar in 1912. A century later, we found that all wild carps in Madagascar derive from this introduction, but most of them are fully scaled (middle picture), though they still carry the “mirror” mutation. This demonstrates a rapid evolution to restore the needed scale cover, using different genes than the original mutated gene. This highlights the efficiency of natural selection to provide alternative solutions for organisms to adapt to their environment.

Reference:
Hubert J.N., Allal F., Hervet C., Ravakarivelo M., Jeney Z., Vergnet A., Guyomard R., Vandeputte M., 2016. How could fully-scaled carps appear in natural waters in Madagascar? Proceedings of the Royal Society B 283: 20160945