Funny you should ask - I actually have the issue on my desk at the moment
I did drop the chap from Blagdon a PM, but didn't get a response. Oh well.
PFk were happy that you could keep goldfish in this but don't mention stocking levels. Quote:
...importantly for the PFK reader, you can sensibly keep fish in them.
In their example they suggested 2 common goldfish or 2 comets to start.
The last paragraph reads: Quote:
So what's the catch? Genuinely, there isn't one. I was a bit dubious about the windows at first, yet once set up you get a view of your pond and its wildlife that you wouldn't otherwise have, so I liked that too. Happy days!