fish appeared

Question
When I cleaned the filter on my pump I noticed fish swimming in the bottom of my pond,I didn't put any fish in there.I have a lily pad I grew from Menards and I recently purchased some water plants from a local garden store.They look similar to minnows but I don't have any idea where they came from or what they are. I know they are not tadpoles.Do you have any idea what they are and where they came from? I just bought some bloodworms to put in there to feed them but I'm not sure if that's what they will eat.
 Any help will be greatly appreciated and any ideas of what to do with the fish when winter comes in Minnesota would be great also because I do empty the pond every winter.
                                   Thank You,
                                       Rochelle

Answer
They are gambusia or some other mosquito fish.  They most likely came in with a plant.  They could have also been carried from another water source by a bird.  They eat mosquito larvae.  You could probably give them away if you can catch them.  They are handy to have around because they lower the mosquito population.  I suppose you could set up an indoor aquarium if you wanted to keep them year-round.