John, when we had shubunkin (goldfish) with our koi, the shubunkins either
interbred with the koi (not sure about this) or ate all the koi fry. We
didn't have koi fry survivors until all the shubunkins were removed (and
given good homes elsewhere). The only differences I could see were the koi
fry were longer and leaner (like a fat exclamation mark), and had barbels
(whiskers). The shubunkin babies were shaped like the 2 inch babies you
found in your pump basket.

Can you net one or two of the live babies and see if you can see barbels?
You might need a magnifying glass.
--
Zk
Oregon, USDA Zone 7
3500gal pond, 13 pond piggies

"John" wrote:
I was sure I had a lot of Koi babies until yesterday, when I cleaned
the pump basket, I found a few "baby Koi" (2 inches) they are REALLY
REALLY like gold fish!!!