All that genetic mutation began in quite a while ago in Asia, when some monks were messing with the Wild Carp's gene pool.  They actually came up with a mutation that makes the carp scaleless (easier to prepare for consumption)!   I believe they're called Leather Carp.  All of these carp mutations are found the U.S.  They are quite a bit rarer than regular Common Carp, though.  I, personally, have only caught Common Carp.  Common Carp are the result of the monks breeding the largest specimens of Wild Carp, so that down through the generations the fish would gradually become larger (for human consumption purposes).  The original Wild Carp was relatively small and only grew to about 10 pounds.  Today, we can catch fish 3 to 4 times that large.   When Common Carp were released into Wild Carp populations in Asia, they genetically destroyed the Wild Carp's original genetic code.  This in turn decimated the "true" Wild Carp.