There seems to be a great deal of progress in breeding jumbo size koi. I was flicking through some 2002 issues of koi mag and also the book "Still Waters" last night. Writers of the various articles were excitedly refering to nisai koi that were about 43-45cm and extolling their fast growth rates.Some of the articles were written only two years ago and they sound like they were from a completely different era or planet! Today it is routine to have tosai of 40cm+,even 50cm+ and nisai of 65cm-70cm. More breeders are reinvigorating their breeding stock with new gene pool by back breeding with magoi.We now get the chance to see faster growing koi with bigger full size potential as well as seemingly stronger koi . Wonder if lifespan and bone structure become more vulnerable with the accelerated growth rate;anyone with longer term experiences ?