I have a pond in my backyard with 2 goldfish in it, they're both about 5 inches long at the moment, I'm guessing the pond is about 50 - 60 gallons. There's caves made of tufa rock and a fountain in the middle. My question is do you think a crayfish would be ok in there with the goldfish? Or more like would the goldfish be ok with the crayfish? Or if not would any other invertebrates be alright in the pond? I live in Canada so it gets quite cold in the winter.