Is there anything that you can do to affect how often you receive gold fish as a gift from your cats or is it completely random? What I've tried so far is save up for the living room expansion so that I have more cats visiting at once which I would hope means more chances for gold fish. However, I feel like I'm getting even less gold fish than before I saved up for the room.
The only thing you can do is get better food and items. The cat stay more time in your yard and that means more chances or getting gold fish. Usually, when a cat can give you more than 50 normal fish, the next time he can give you gold fish. Also, there are rare cats that usually give you more gold fish than others.
Just try to have the best food and items.