Do goldfish shed their scales?

I've heard a while ago that some fish shed their scales periodically, just like birds shed their feathers and regrow new ones. So I've done some research on this on the internet and, well, the verdict is: NO. Goldfish do not shed their scales. Yikes! Why am I asking this? Because in the last week, since the second last change of their water, both Lady Lydia and Pinkie have lost some scales. Not good.

The research suggested they are stressed. I'm pretty sure water conditions are fine as I have tested Ammonia and Nitrite last week and they were both zero. I guess I should check the Nitrate as well, but that usually has not been an issue. Water pH should be the same as I always use the same water and condition it the same way. I did, however, notice they were terribly skittish after that water change. Darting around like crazy when I approached the tank, even bumping into things. As if they have never seen me before or never had their water changed in the past. Silly fish.

Oh well, I guess I'll have to check the Nitrate levels just to be sure and make put a heater in set on very low to make sure the water temperature is at least constant. Maybe the fluctuations due to winter are bothering them. Thankfully they still are eating like horses. Gotta keep an eye on them. Hmmm, no one ever told me owning fish would be like having kids - there is always something!