I'm surprised that no-one has mentioned having frogspawn yet. The first two splodges arrived in my pond on 24 February and since then three more have appeared. I never hear the frogs as my double-glazing is so soundproof I don't even hear the rain and am quite often surprised to open the front door to find it pelting down!
I haven't lost any fish over this hard winter - but there is one large goldfish that is terribly bloated - poor thing is almost as wide as it is long. It has been this way all winter but it doesn't seem to be bothered about it or stressed in any way. I googled a bit and found several possible reasons for bloating - none of which seem to apply as the fish seems quite contented.
The water is crystal clear so that I have also noticed an old shubunkin which seems to have a fondness for a specific spot under the hose which runs from the pump to the filter box. I guess it enjoys the vibration from the pump on its back.