I think it is more common with the Go - Sanke varieties ( Kohaku, Taisho Sanke, Showa ) but also with other Koi with shiroji ( white skin / scales )
such as Shiro Utsuri, Shiro Bekko etc.
At some point at the beginning of a bloodline, a Magoi ( black Koi ) and / or a White Magoi, will have been used, it is just those genes which cause it.
In Japan, the top breeders cull ( kill ) 80 - 90 % of ALL fry !!! in various stages in the first few months !
An Oyagoi set ( parents ) can fertilise up to 300,000 eggs in a single spawning
BUT only a very few escape the first cull, let alone the subsequent culls.
I'm sure British breeders are nowhere near as ruthless, prefering to sell them in bulk rather than culling,
whereas in fact they should actually be culling an even higher %
as our British water does NOT suit growing and developing Koi.
A bloodline which does well in Japanese water is UNLIKELY to do well in British water !
Peter.
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