| Mike , as a history student you'll probably get this but for the sake of others
I'll explain that a few decades back shiro utsuri types as well as showa, would easily get pigeon breasted,or called doubled stomached etc and these blooded koi seemed to have that problem.
Today's modern breeders with all their crosses into sanke and kohaku to benefit color have also done us a favor to breed out that propensity.
In fairness you can over feed and not let them experience winter and contribute to the situation. |