Question
I have a few large Koi and some mature Rosie Reds. Then I ended up with a lot of babies. About 2 dozen.  But some of the babies are orange and a few are black.  Do Koi interbreed with other fish?? Quite as few do look like Koi, though. Do you think that they would live thru a Chicago winter? And my pond is about 1500 gallons and 3 feet deep at the most. And how many fish do you think this size pond could support?  Thanks for any answer that you can give.   Joyce

Answer
I have heard cases of koi (cyprinus carpio) and goldfish (carassius auratus) breeding.  It is rare but it is still possible due to their genetic similarities.  The rosy red minnow (pimephales promelas) also has the genetic similarities necessary to cross-breed but I have never personally heard of this before.  I will not discount its possibility seeing that koi, goldfish, and reds are all in the family cyprinidae.

The babies you have described could be (Koi x Koi) or (Koi X Rosy Red).  I doubt that they are full rosy reds because they would most likely all be orange from birth.  The reason they are different in colors is the same reason that some litters of kittens have differing patterns.  You will be able to tell what they are better by 6-8 weeks after hatching.  Koi will have prominent barbels near their mouth and a distinctive overhead profile.

There is a very strong chance that most of them will live through the winter because of the appropriate depth of your pond.  Just make sure to put a hole in the ice if the whole pond surface freezes over.  

Keep this in mind; 10 small fish whose weight adds up to 3 lbs produce less waste than one 3 lb. fish.  While they are babies, don't worry too much about it.  On the other hand, I wouldn't stock more than 5 koi over 18" in a 1,500 gallon pond.