Must have been a shallow pond if he is frozen into the ice. More likely he suffocated, due to lack of oxegen in the water if the pond has been frozen for a while.
One of my fish, I thought ,had gone tits up the other day. Laying on the bottom on it's side. I fished it out with a net flipped it over a few times to see if it was diseased or anything and then left it sitting in the net in the water when I heard the phone go.
I forgot about it until later in the day and when I went back the bugger was with the rest at the bottom.
Maybe he was pretending.
Just as well I didn't lob him in the bin or something.