Mirror carp are a type of fish, commonly found in Europe. Mirror carp are a variety of the common carp (Cyprinus carpio) developed through selective breeding. The name “mirror carp” originates from their scales’ resemblance to mirrors. They can grow in excess of 60lb – the last few British record fish have all been mirror carp.
The difference between mirror and common carp can largely be reduced to the presence of the large mirror-like scales on the former. The mirror-scale phenotype is caused by a genetic mutation for which there are two alleles (i.e., forms of a gene) denoted as the S and the N alleles. The genotype coding for the recess mirror scales is “ssnn” (all recessive). Common carp have an even, regular scale pattern, whereas mirrors have irregular and patchy scaling, making many fish unique and possible to identify individual fish by sight, leading to most carp in the UK over 40 lb being nicknamed. Mirror carp usually belong to the common carp’s nominate subspecies, C. c. carpio.
This lack of scales is widely believed to have been bred in by monks to make the fish easier to prepare for the table.
Contrary to popular belief, a leather carp is not a mirror carp without scales; a distinct genetic difference exists. Leather carp are permitted a few scales either along the dorsal line or the wrist of the tail. Leather carp also have reduced numbers of red blood cells, slowing growth rates, which makes larger leather carp extremely sought after and rare. The biggest known was Heather the Leather at 52 lb (24 kg).