I too lost my fish last winter... 11 or so koi... 2 comets... 2 goldfish...
died when I forgot to shut off the darn hose during a winter fill up. In
addition I thought all was lost and when my hoop house collapsed in 30+
inches of snow this Feb. so I shut everything off and let her freeze. Much
to my surprise during spring cleanup I actually had all my lillies and other
plants survive... and who would have knew a goldfish (now called Lucky) and,
of course, all the indestructable mosquito fish in my pond. So just last
Saturday while training my new Koi to hand feed I found yet another
surprise... a mysterious black goldfish joined in the feeding. I had a few
babies last year before I went on my killing spree... but I thought they
were all lost (under 2 inches at the time). This guy is already around 6
inches in length and has quite a tummy on him. He does blend into the liner
quite well.... so I am not surprised I didn't see him.

For my experiment this year I have put Blue Gill in the pond too. They get
along great with the koi and are a ton of fun. When I pull string algae
from the side of the liner the blue gill line up to attack any mosquito fish
babies that get thrown out of there algae homes. Blue Gill have also have
no fear... as they try to eat my fingers ever time too... They also seem to
like to jump right in my fish net while I am trying to isolate other fish.
Overall, this season has been quite fun so far.