As for longfins I think they can add a little something to a pond. But at this point not my pond.

Here's a picture of the lingfin that is in our pond right now. I can do one of two thing. Just add one more koi to the pond, or move this koi out of the pond, so I don't have to bring the number of koi up by one. The problem if I bring the number up by one is, I would want another koi than this one.
Tom