i read that goldfish do not digest sugar well, so are fruit good for goldfish?

Fruit is good for goldfish as a treat because you are right in that they don't digest sugar well. I've heard that most people only feed their goldfish fruit about once a week.

In my opionion, goldfish can live their whole lives without ever eating fruit. I have never given fruit to mine. They do get spirulina flakes, peas and occasional zuchinni that is steamed a bit.

They also entertain themselves by eating the algae that I have let grow on the back wall of their tank.

Fruits are fine occasionally (no more than once a week).