If the water doesn't freeze to the bottom and you have a small number of minnows relative to the deep part of the pond volume, they probably don't need anything. To be sure they make it, you can set up a bubbler. I just use a standard aquarium dual output air pump in a waterproof container to feed two airstones. The pond does close up when the weather is really cold but the bubblers break through as soon as it warms up. You have to keep the snow of the area though.

Thanks. Adding a bubbler sounds like a minor precuation for the extra insurance it would give. I had a lot of trouble getting minnows established. I would hate to lose them. They are my mosquito control.

The pond is about 4 feet deep in the center, so I feel confident that it won't freeze to the bottom. I don't really know how many minnows I have because once the water warmed enough for them to start breeding, they were in hiding, guarding their eggs. I will guess that there are perhaps 4 dozen, some adults and some juveniles. The pond holds about 3,000 gallons of water.

Your winters are a lot harsher than what we get here in Boulder, Colorado. If you can overwinter without running a pump, I certainly ought to be able to.

You should try rosy reds. They are a pink form of the fathead minnow and are bright enough that they are easier to count than dark backed minnows against a dark bottom.

Where do you buy Rosy Reds? Are they a pet store item? I bought the minnows at bait shops.

Most fish/pet supply stores sell them as feeder fish and keep them crammed in unhealthy conditions so expect a quite few to die but they are cheap.

Now that you have a healthy bunch of fish, make sure you quarantine any new ones for two weeks or better 3 weeks in an aquarium or large tub. Also, the natural color is dominant so any next generation natural + rosy will mostly give you dark. They only live about 3 years.