Disposal of Koi

Hi there are groups on Facebook for people who are aquarist here imagine if you share there someone will take them. Poisson en belquie a vender ou a donner for example

The "deuxième main" website has an animals section (and I suspect it isn't that policed - I was a bit shocked when I checked it out just now to see an 8-week old puppy just being given away) so you could put your fish on that, in my experience anything of value (and Koi are quite expensive, in fact) going for free gets snapped up pretty quickly.

Try Antwerp zoo.

Also try contacting the zoos and aquariums in Belgium on this website: https://www.tripadvisor.com/Attractions-g188634-Activities-c48-Belgium.html