Bass, water snakes, turtles, herons.
Bluegill should be kept in a large pond they are a sport fish rather than an aquarium fish and they're regarded as good eating too.
Bass and bluegill are nearly always used together to stock farm ponds. The bass eat bluegill to keep the population in check, and bluegills will eat bass eggs, so a balance is kept.
Three types of forest populations that could not survive in a pond ecosystem are monkeys, ants, and birds.
It needs to be atleast 2 ft deep if you want to keep the fish in the cold weather however i would suggest going much deeper to be on the safe size, a small pond can have steep sides to dig to about 3 ft and there will be no problems with the fish in cold weather, other than that it is not important how deep the pond is, as long as they can swim freely.
they can be shallow or deep.
Bluegill fish can be found in freshwater lakes, ponds, and rivers across North America. They prefer shallow waters with plenty of vegetation to provide cover and food sources. Look for Bluegill fish in areas with slow-moving or still water, like near docks, fallen trees, or weed beds.
Goldfish can survive in a pond without a pump, but it is important to ensure that the pond has enough oxygen and is properly maintained to support their health and well-being.
The pond water must contain high nitrogen levels.
If the pond is not deep, the fish can leave the pond. It is important to take good care of them or they will be tempted to leave.
sea
If the water freezes but the pond is deep enough for the fish to still be in water at the bottom there is a good chance they will survive. If all of the water freezes however and the fish become frozen solid then I'm afraid they are unlikely to survive.