if they are koi babies they will tend to grow a bit faster and color up sometimes sooner (shubunkins will also sometimes color faster then goldfish)...although I have koi babies from last year that are still a grayish brown. A sure fire way to tell if they are koi is if they have the barbels (whiskers) goldfish do not have them, but they have to be large enough so you can see them. More likely then not they are goldfish babies, they breed better, but one can not tell for sure with out a close inspection, I thought those 2 of mine were goldfish and almost culled them.