I'm doing some testing at the moment. For starters, I'm stocking the pond with ten of one fish. Not all perfect, but I'm making sure there are some perfect specimens of each variety. If that doesn't work, I'll try stocking with 10 perfect of each kind, but that does seem silly when using fish bowls, you only need 1 perfect.
Norma
*edit* Not looking good so far. I have stocked the pond with 6 different varieties making sure there were a few perfects of each. When I hover over his lifetime wish though, it says I have 0 of 13 perfect fish.