I know its almost a year since this was posted, but I'd like to add my take.
Adding fish back into native streams after you've had them in a pond would most likely be frowned upon by your Fish and Wildlife officials. You could be introducing them to diseases and parasites from your plants which would then get into your stream. Even taking fish out live (which is illegal in NJ, unless you have a permit) and keeping them for a summer and returning would be questionable. Ursula's idea of the Paradise Fish is much better. I use White Cloud Mountain Fish. I bring them into an aquarium over winter. They don't need heat over winter in any home. They should breed for you as well as long as you have floating plants like Hornwort or Ceratophyllum.
