Specially-bred “Mirror” Carp Quickly Regained Their Scales Through Natural Selection

A group of carp originally bred to have fewer scales have quickly evolved to have full scale cover again. Interestingly, this happened without the loss of the original gene mutation. The findings are in a paper just published in the journal Proceedings of the Royal Society B.

The common carp (Cyprinus carpio) is a large freshwater fish known for its ability to quickly adapt to new environments. This makes the fish a destructive invasive species in many areas since released carp have no problems surviving and reproducing. Carp can be a reliable source of food but their scales make them difficult to prepare for eating. This led Europeans to breed “mirror carp”, carp with so few scales that they take on a reflective appearance.

In the early 20th century, mirror carp were released into bodies of water in Madagascar. The idea was to give the locals a constant source of food. The fish thrived in the new environment and their population quickly exploded. Over time, however, there were more and more reports of scaly carp. Currently, most of the carp in the area have gotten their scales back, leading researchers to investigate how this happened so fast.

Researchers from France, Hungary, and Madagascar collaborated to investigate the genetics of the carp population. The original mirror carp had a mutation that caused loss of function in the scale cover gene fgfr1a1. The team found that even though all of the carp still had the mutation, over 60% of caught fish were fully scaled. This means that the fish didn’t lose the mutation but instead evolved their scales back through different genes. In less than 40 generations, the carp had reverted back to a wild-type scale cover.

The authors note that the carp evolved their scales back in a very short amount of time from an evolutionary perspective. In a bit under a century, the fish gained scale cover while retaining the original mirror mutation. The team speculates that natural selection heavily favored scaled fish since scales protect fish from predators, parasites, and other dangers.


Jean-Noël Hubert et al. How could fully scaled carps appear in natural waters in Madagascar?. Proceedings of the Royal Society B: Biological Sciences (2016).

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