layer the fish and the ice dont just pile ice on top. or vise versa. at 3 full days when u clean them, you will get a funky smell from the innards starting to gas a bit, strange smell, but still ok. drain the water that comes from the melted ice now and then,
This. Especially the first part. Letting them sit in water will make them mushy. Make sure there's some red to the gills still.