memorable goldfish

I've always been sceptical of the 'goldfish has a 20 second memory' claim which apparently ws proved by experiment.
Having recently moved house and 'inherited' a pond which we stocked with a few goldfish to see the quality of the water, I have the following observations.
As there were only 5 of them and it was just to check the water quality, we didnt feed them.
They thrived ,ok there were quite a few tadpoles and the pond is reasonable size 12m3 ish , but that doesn't smack of amnesiac hunters to me
So someone else bought some more. The first few times we put food on the surface, zilch , they stayed in hiding or zipped about. Then they started to know that when they see someone and stuff goesonto the surface that means GRUB UP.
So I feel that the experiment that was done years ago , must have been done with a psychotic goldfish [ if it was a goldfish that had been kept in a small bowl, I'm not that surprised either ]