There
are 4 main scale patterns displayed by carp:
The Fully scaled carp known as the Common or Wild carp

The Mirror carp displaying a small number of large, randomly skattered scales
on the body.
The Linear carp has a single row of scales along the lateral line.

The Leather carp shows very few if not any scales on the body.
(Arnie at a staggering 32lb 8ozs picture courtesy of ueasaac)
All true carp are fully scaled but with the introduction of semi-domestication
around the 16th Century, varieties of carp without scales were bred. Different
body shapes were also selected, with the aim of producing deep bodied fish
with very few scales which would be easier to clean and fit nicely on a
plate!
Other varieties
of carp include the fully scaled mirror carp, ghost carp (common carp cross
bread with a Koi carp) and crucian carp.
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