I have lots of fish in my pond many over 20 years old, however we are looking to fill it in this year, and would like to know how to go about selling or giving them away.
some of the large pet supermarket type places (and smaller pet shops)have small ads boards that you might consider....Is there a local fish fanciers club? Failing that you might try freecycle.
If your koi are big then a local water garden centre might be intersted in buying to sell on